LogTape

https://logtape.org/
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LogTape is a zero-dependency, library-first structured logging library for JavaScript and TypeScript...
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### Setup using install() function

Source: https://logtape.org/manual/adaptors

Use the install function to programmatically route logs to log4js.

```typescript
import log4js from "log4js";
import { install } from "@logtape/adaptor-log4js";

log4js.configure({
  appenders: { out: { type: "stdout" } },
  categories: { default: { appenders: ["out"], level: "info" } }
});

// With default options (category-based loggers)
install(log4js);

// Now any LogTape-enabled library will log through log4js
import { getLogger } from "@logtape/logtape";
const logger = getLogger("my-app");
logger.info("This will be logged through log4js");
```

--------------------------------

### Quick setup with auto-installer

Source: https://logtape.org/manual/adaptors

Integrate LogTape with log4js by importing the install module.

```typescript
import log4js from "log4js";

// Configure log4js first
log4js.configure({
  appenders: { out: { type: "stdout" } },
  categories: { default: { appenders: ["out"], level: "info" } }
});

// Simply import to automatically set up the adapter
import "@logtape/adaptor-log4js/install";

// Now all LogTape logs will be routed to log4js
import { getLogger } from "@logtape/logtape";
const logger = getLogger("my-app");
logger.info("This will be logged through log4js");
```

--------------------------------

### Install @logtape/graphql-yoga

Source: https://logtape.org/manual/integrations

Installation commands for various JavaScript runtimes.

```Deno
deno add jsr:@logtape/graphql-yoga
```

```npm
npm add @logtape/graphql-yoga
```

```pnpm
pnpm add @logtape/graphql-yoga
```

```Yarn
yarn add @logtape/graphql-yoga
```

```Bun
bun add @logtape/graphql-yoga
```

--------------------------------

### Complete Configuration Examples

Source: https://logtape.org/manual/config

Full configuration examples provided in both JSON and YAML formats.

```json
{
  "sinks": {
    "console": {
      "type": "#console()",
      "formatter": {
        "type": "#ansiColor()",
        "timestamp": "date-time-tz"
      }
    },
    "file": {
      "type": "@logtape/file#getFileSink()",
      "path": "/var/log/app.log",
      "formatter": "#jsonLines()"
    }
  },
  "loggers": [
    {
      "category": ["myapp"],
      "sinks": ["console", "file"],
      "lowestLevel": "info"
    }
  ]
}
```

```yaml
sinks:
  console:
    type: "#console()"
    formatter:
      type: "#ansiColor()"
      timestamp: date-time-tz

  file:
    type: "@logtape/file#getFileSink()"
    path: /var/log/app.log
    formatter: "#jsonLines()"

loggers:
- category: [myapp]
  sinks: [console, file]
  lowestLevel: info
```

--------------------------------

### Install LogTape

Source: https://logtape.org/manual/install

Standard installation commands for different package managers and runtimes.

```sh
deno add jsr:@logtape/logtape
```

```sh
npm add @logtape/logtape
```

```sh
pnpm add @logtape/logtape
```

```sh
yarn add @logtape/logtape
```

```sh
bun add @logtape/logtape
```

--------------------------------

### Install @logtape/file package

Source: https://logtape.org/sinks/file

Installation commands for various JavaScript runtimes.

```sh
deno add jsr:@logtape/file
```

```sh
npm add @logtape/file
```

```sh
pnpm add @logtape/file
```

```sh
yarn add @logtape/file
```

```sh
bun add @logtape/file
```

--------------------------------

### Install @logtape/express

Source: https://logtape.org/manual/integrations

Installation commands for various package managers.

```Deno
deno add jsr:@logtape/express
```

```npm
npm add @logtape/express
```

```pnpm
pnpm add @logtape/express
```

```Yarn
yarn add @logtape/express
```

```Bun
bun add @logtape/express
```

--------------------------------

### Configure Shared Setup File

Source: https://logtape.org/manual/testing

Configure LogTape in a shared setup file and register it in the Vitest configuration.

```typescript
import { defineConfig } from "vitest/config";

export default defineConfig({
  test: {
    setupFiles: ["./test/setup-logtape.ts"],
  },
});
```

```typescript
import { AsyncLocalStorage } from "node:async_hooks";
import { configure } from "@logtape/logtape";

await configure({
  contextLocalStorage: new AsyncLocalStorage(),
  sinks: {},
  loggers: [
    { category: ["logtape", "meta"], sinks: [] },
  ],
});
```

--------------------------------

### Incorrect configuration example

Source: https://logtape.org/lint/require-meta-sink

This example demonstrates a configuration missing the required meta logger entry.

```typescript
import { configure } from "@logtape/logtape";

await configure({
  sinks: { console: consoleSink },
  loggers: [
    // No meta logger entry → diagnostics fall back to the built-in console sink
    { category: ["my-app"], sinks: ["console"] },
  ],
});
```

--------------------------------

### Correct configuration example

Source: https://logtape.org/lint/require-meta-sink

This example shows the correct way to include a meta logger entry using either ['logtape'] or ['logtape', 'meta'] categories.

```typescript
import { configure } from "@logtape/logtape";

await configure({
  sinks: { console: consoleSink },
  loggers: [
    { category: ["my-app"], sinks: ["console"] },
    // Either array form is accepted:
    { category: ["logtape"], sinks: ["console"] },
    // or:
    { category: ["logtape", "meta"], sinks: ["console"] },
  ],
});
```

--------------------------------

### Install Pino adaptor automatically

Source: https://logtape.org/manual/adaptors

Use the install() function to automatically route all LogTape logs to a Pino logger.

```typescript
import { pino } from "pino";
import { install } from "@logtape/adaptor-pino";

const pinoLogger = pino({
  level: "info",
  transport: {
    target: "pino-pretty"
  }
});

// Install with custom logger and options
install(pinoLogger, {
  category: {
    position: "start",
    decorator: "[]",
    separator: "."
  }
});

// Now any LogTape-enabled library will log through Pino
import { getLogger } from "@logtape/logtape";
const logger = getLogger("my-app");
logger.info("This will be logged through Pino");
```

--------------------------------

### Install @logtape/testing-vitest

Source: https://logtape.org/manual/testing

Commands to install the testing package using various package managers.

```npm
npm add @logtape/testing-vitest
```

```pnpm
pnpm add @logtape/testing-vitest
```

```Yarn
yarn add @logtape/testing-vitest
```

```Bun
bun add @logtape/testing-vitest
```

```Deno
deno add jsr:@logtape/testing-vitest npm:vitest
```

--------------------------------

### Shared Preload Module Setup

Source: https://logtape.org/manual/testing

Configure LogTape once in a shared module and preload it during test execution to avoid per-file setup.

```javascript
import { AsyncLocalStorage } from "node:async_hooks";
import { configure } from "@logtape/logtape";

await configure({
  contextLocalStorage: new AsyncLocalStorage(),
  sinks: {},
  loggers: [
    { category: ["logtape", "meta"], sinks: [] },
  ],
});
```

```bash
node --import ./test/setup-logtape.mjs --test
```

```typescript
import { test } from "@logtape/testing-node";
import { getLogger } from "@logtape/logtape";

test("case", async () => {
  getLogger(["my-lib"]).info("Fixture state: {state}.", {
    state: "ready",
  });

  // Run assertions.  The info log is printed only if this test fails.
});
```

--------------------------------

### Use setupLogTape in a test file

Source: https://logtape.org/manual/testing

Demonstrates importing and executing the setup function before running tests.

```typescript
import { test, expect } from "@logtape/testing-vitest";
import { getLogger } from "@logtape/logtape";
import { setupLogTape } from "./setup-logtape.ts";

await setupLogTape();

test("case", () => {
  getLogger(["my-lib"]).info("Fixture state: {state}.");

  expect(1 + 1).toBe(2);
  // The info log is printed only if this test fails.
});
```

--------------------------------

### Install @logtape/pretty package

Source: https://logtape.org/manual/formatters

Commands to install the pretty formatter package using various package managers.

```sh
deno add jsr:@logtape/pretty
```

```sh
npm add @logtape/pretty
```

```sh
pnpm add @logtape/pretty
```

```sh
yarn add @logtape/pretty
```

```sh
bun add @logtape/pretty
```

--------------------------------

### Install LogTape Hono adapter

Source: https://logtape.org/manual/integrations

Installation commands for the @logtape/hono package across different JavaScript runtimes.

```sh
deno add jsr:@logtape/hono
```

```sh
npm add @logtape/hono
```

```sh
pnpm add @logtape/hono
```

```sh
yarn add @logtape/hono
```

```sh
bun add @logtape/hono
```

--------------------------------

### Install with custom logger and options

Source: https://logtape.org/manual/adaptors

Uses the install function to apply custom Winston logger instances and specific level mappings.

```typescript
import winston from "winston";
import { install } from "@logtape/adaptor-winston";

const customLogger = winston.createLogger({
  transports: [new winston.transports.File({ filename: "app.log" })]
});

// Install with custom logger and options
install(customLogger, {
  category: { position: "start", decorator: "[]" },
  levelsMap: {
    "trace": "silly",
    "debug": "debug",
    "info": "verbose",
    "warning": "info",
    "error": "warn",
    "fatal": "error",
  }
});
```

--------------------------------

### Configure linting rules

Source: https://logtape.org/lint/prefer-lazy-evaluation

Configuration examples for ESLint and Deno Lint.

```javascript
import logtape from "@logtape/lint/eslint";

export default [
  {
    plugins: { "@logtape": logtape },
    rules: {
      "@logtape/prefer-lazy-evaluation": "warn",
    },
  },
];
```

```json
{
  "unstable": ["lint"],
  "lint": {
    "plugins": ["jsr:@logtape/lint/deno"],
    "rules": {
      "include": ["logtape/prefer-lazy-evaluation"]
    }
  }
}
```

--------------------------------

### Setup LogTape via top-level function

Source: https://logtape.org/manual/testing

Call a shared setup function at the top level of each test file if preloading is not feasible.

```typescript
import { AsyncLocalStorage } from "node:async_hooks";
import { configure } from "@logtape/logtape";

let configured = false;

export async function setupLogTape(): Promise<void> {
  if (configured) return;
  configured = true;

  await configure({
    contextLocalStorage: new AsyncLocalStorage(),
    sinks: {},
    loggers: [
      { category: ["logtape", "meta"], sinks: [] },
    ],
  });
}
```

```typescript
import { test } from "@logtape/testing-bun";
import { getLogger } from "@logtape/logtape";
import { setupLogTape } from "./setup-logtape.ts";

await setupLogTape();

test("case", () => {
  getLogger(["my-lib"]).info("Fixture state: {state}.");

  // Run assertions.  The info log is printed only if this test fails.
});
```

--------------------------------

### Setup LogTape via top-level function

Source: https://logtape.org/manual/testing

Call a shared setup function at the top level of each test file if preloading is not feasible.

```typescript
import { AsyncLocalStorage } from "node:async_hooks";
import { configure } from "@logtape/logtape";

let configured = false;

export async function setupLogTape(): Promise<void> {
  if (configured) return;
  configured = true;

  await configure({
    contextLocalStorage: new AsyncLocalStorage(),
    sinks: {},
    loggers: [
      { category: ["logtape", "meta"], sinks: [] },
    ],
  });
}
```

```typescript
import { test } from "@logtape/testing-deno";
import { getLogger } from "@logtape/logtape";
import { setupLogTape } from "./setup-logtape.ts";

await setupLogTape();

test("case", () => {
  getLogger(["my-lib"]).info("Fixture state: {state}.");

  // Run assertions.  The info log is printed only if this test fails.
});
```

--------------------------------

### Install LogTape

Source: https://logtape.org/

Command to add the LogTape package to your project using Deno.

```bash
deno add jsr:@logtape/logtape
```

--------------------------------

### Install Unstable LogTape

Source: https://logtape.org/manual/install

Commands to install the development version of LogTape.

```sh
npm add @logtape/logtape@dev
```

```sh
pnpm add @logtape/logtape@dev
```

```sh
yarn add @logtape/logtape@dev
```

```sh
bun add @logtape/logtape@dev
```

--------------------------------

### Install LogTape Deno testing package

Source: https://logtape.org/manual/testing

Add the testing package to your Deno project.

```bash
deno add jsr:@logtape/testing-deno
```

--------------------------------

### Install testing package

Source: https://logtape.org/manual/library

Commands to add the @logtape/testing package to your project.

```bash
deno add jsr:@logtape/testing
```

```bash
npm add @logtape/testing
```

```bash
pnpm add @logtape/testing
```

```bash
yarn add @logtape/testing
```

```bash
bun add @logtape/testing
```

--------------------------------

### Correct usage examples

Source: https://logtape.org/lint/no-unawaited-log

Examples showing valid ways to handle log calls with async callbacks, including awaiting, returning, and concise arrow function bodies.

```typescript
import { getLogger } from "@logtape/logtape";
const logger = getLogger(["my-app"]);

async function handler() {
  // Awaited:
  await logger.debug("Data: {d}.", async () => ({ d: await fetchData() }));

  // Returned (caller is responsible for awaiting):
  return logger.debug("Data: {d}.", async () => ({ d: await fetchData() }));
}

// Concise arrow body propagates the promise:
const logData = async () =>
  logger.debug("Data: {d}.", async () => ({ d: await fetchData() }));
```

--------------------------------

### Top-level Setup Function

Source: https://logtape.org/manual/testing

Define a shared setup function to be called at the top level of each test file if preloading is not possible.

```typescript
import { AsyncLocalStorage } from "node:async_hooks";
import { configure } from "@logtape/logtape";

let configured = false;

export async function setupLogTape(): Promise<void> {
  if (configured) return;
  configured = true;

  await configure({
    contextLocalStorage: new AsyncLocalStorage(),
    sinks: {},
    loggers: [
      { category: ["logtape", "meta"], sinks: [] },
    ],
  });
}
```

```typescript
import { test } from "@logtape/testing-node";
import { getLogger } from "@logtape/logtape";
import { setupLogTape } from "./setup-logtape.ts";

await setupLogTape();

test("case", async () => {
  getLogger(["my-lib"]).info("Fixture state: {state}.");

  // Run assertions.  The info log is printed only if this test fails.
});
```

--------------------------------

### Install Drizzle ORM adapter

Source: https://logtape.org/manual/integrations

Commands to install the @logtape/drizzle-orm package using various package managers.

```sh
deno add jsr:@logtape/drizzle-orm
```

```sh
npm add @logtape/drizzle-orm
```

```sh
pnpm add @logtape/drizzle-orm
```

```sh
yarn add @logtape/drizzle-orm
```

```sh
bun add @logtape/drizzle-orm
```

--------------------------------

### Environment variable expansion syntax

Source: https://logtape.org/manual/config

Example configuration showing the use of default values in environment variable expansion.

```json
{
  "sinks": {
    "file": {
      "type": "@logtape/file#getFileSink()",
      "path": "${LOG_PATH:/var/log/app.log}"
    }
  }
}
```

--------------------------------

### Install @logtape/adaptor-pino

Source: https://logtape.org/manual/adaptors

Commands to add the Pino adaptor package using various package managers.

```Deno
deno add jsr:@logtape/adaptor-pino
```

```npm
npm add @logtape/adaptor-pino
```

```pnpm
pnpm add @logtape/adaptor-pino
```

```Yarn
yarn add @logtape/adaptor-pino
```

```Bun
bun add @logtape/adaptor-pino
```

--------------------------------

### Install Bunyan adapter automatically

Source: https://logtape.org/manual/adaptors

Use the install function to route all LogTape logs to a Bunyan logger instance.

```typescript
import bunyan from "bunyan";
import { install } from "@logtape/adaptor-bunyan";

const bunyanLogger = bunyan.createLogger({ name: "my-app", level: "info" });

// Install with custom logger and options
install(bunyanLogger, {
  category: {
    position: "start",
    decorator: "[]",
    separator: "."
  }
});

// Now any LogTape-enabled library will log through Bunyan
import { getLogger } from "@logtape/logtape";
const logger = getLogger("my-app");
logger.info("This will be logged through Bunyan");
```

--------------------------------

### Install LogTape Bun testing package

Source: https://logtape.org/manual/testing

Add the testing package to your project dependencies.

```bash
bun add @logtape/testing-bun
```

--------------------------------

### Configuring LogTape in an application

Source: https://logtape.org/comparison

Example of how an application can configure LogTape to capture logs from a library.

```typescript
// In your application
import { configure, getConsoleSink } from "@logtape/logtape";
import { processData } from "some-library";

await configure({
  sinks: {
    console: getConsoleSink(),
  },
  loggers: [
    { category: ["some-library"], lowestLevel: "debug", sinks: ["console"] },
  ],
});

processData([1, 2, 3]); // Now you'll see the library's logs
```

--------------------------------

### Configure LogTape with GraphQL Yoga

Source: https://logtape.org/manual/integrations

Basic setup showing how to configure LogTape and pass the logger to the Yoga server instance.

```typescript
import { configure, getConsoleSink } from "@logtape/logtape";
import { getYogaLogger } from "@logtape/graphql-yoga";
import { createSchema, createYoga } from "graphql-yoga";

await configure({
  sinks: { console: getConsoleSink() },
  loggers: [
    { category: ["graphql-yoga"], sinks: ["console"], lowestLevel: "debug" }
  ],
});

const yoga = createYoga({
  schema: createSchema({
    typeDefs: /* GraphQL */ `
      type Query {
        hello: String!
      }
    `,
    resolvers: {
      Query: {
        hello: () => "world",
      },
    },
  }),
  logging: getYogaLogger(),
});
```

--------------------------------

### Configure Database Logging with AsyncSink

Source: https://logtape.org/manual/sinks

Example of integrating an asynchronous database insertion into the LogTape configuration.

```typescript
// @noErrors: 2345
interface Database {
  /**
  * A hypothetical table interface.
  */
  readonly logs: Table<"logs">;
}
interface Table<TableName extends string> {
  /**
   * A hypothetical method to insert a record into the table.
   */
  insert(record: TableRecord<TableName>): Promise<void>;
}
interface TableRecord<TableName extends string> {
  timestamp: number;
  level: string;
  category: string;
  message: string;
  properties: string;
}
/**
 * A hypothetical database interface.
 */
const db = null as unknown as Database;
// ---cut-before---
import { type AsyncSink, configure, fromAsyncSink } from "@logtape/logtape";

const databaseSink: AsyncSink = async (record) => {
  await db.logs.insert({
    timestamp: record.timestamp,
    level: record.level,
    category: record.category.join("."),
    message: record.message.join(""),
    properties: JSON.stringify(record.properties),
  });
};

await configure({
  sinks: {
    database: fromAsyncSink(databaseSink),
  },
  loggers: [
    { category: [], sinks: ["database"], lowestLevel: "info" },
  ],
});
```

--------------------------------

### Install log4js adapter

Source: https://logtape.org/manual/adaptors

Commands to add the log4js adapter dependency to your project.

```sh
deno add jsr:@logtape/adaptor-log4js
```

```sh
npm add @logtape/adaptor-log4js
```

```sh
pnpm add @logtape/adaptor-log4js
```

```sh
yarn add @logtape/adaptor-log4js
```

```sh
bun add @logtape/adaptor-log4js
```

--------------------------------

### Install skills-npm as a development dependency

Source: https://logtape.org/manual/llm

Install the skills-npm package using your preferred package manager to enable automatic skill synchronization.

```bash
npm install -D skills-npm
```

```bash
pnpm add -D skills-npm
```

```bash
yarn add -D skills-npm
```

```bash
bun add -D skills-npm
```

--------------------------------

### Install @logtape/testing-node

Source: https://logtape.org/manual/testing

Commands to add the testing package using various Node.js package managers.

```bash
npm add @logtape/testing-node
```

```bash
pnpm add @logtape/testing-node
```

```bash
yarn add @logtape/testing-node
```

```bash
bun add @logtape/testing-node
```

--------------------------------

### Correct Code Examples

Source: https://logtape.org/lint/no-message-interpolation

Examples that comply with the rule, including structured templates, plain strings, and tagged templates.

```typescript
import { getLogger } from "@logtape/logtape";
const logger = getLogger(["my-app"]);

logger.info("User {userId} logged in.", { userId });
logger.error("Request {reqId} failed.", { reqId });
logger.debug("Processing {count} items.", { count: items.length });

// Plain backtick strings without ${} are allowed
logger.info(`User logged in.`);

// Tagged template literals (LogTape template syntax) are allowed
logger.info`User ${userId} logged in.`;
```

--------------------------------

### Install @logtape/elysia

Source: https://logtape.org/manual/integrations

Commands to add the LogTape Elysia plugin using various package managers.

```sh
deno add jsr:@logtape/elysia
```

```sh
npm add @logtape/elysia
```

```sh
pnpm add @logtape/elysia
```

```sh
yarn add @logtape/elysia
```

```sh
bun add @logtape/elysia
```

--------------------------------

### Library logging with LogTape

Source: https://logtape.org/comparison

Example of a library using LogTape to log without requiring configuration.

```typescript
// In some-library/index.js
import { getLogger } from "@logtape/logtape";

const logger = getLogger(["some-library"]);

export function processData(data) {
  logger.info("Processing data with {size} items.", { size: data.length });
  // ... process data
}
```

--------------------------------

### Install @logtape/adaptor-winston

Source: https://logtape.org/manual/adaptors

Commands to add the Winston adaptor package to your project using different package managers.

```sh
deno add jsr:@logtape/adaptor-winston
```

```sh
npm add @logtape/adaptor-winston
```

```sh
pnpm add @logtape/adaptor-winston
```

```sh
yarn add @logtape/adaptor-winston
```

```sh
bun add @logtape/adaptor-winston
```

--------------------------------

### Install @logtape/adaptor-bunyan

Source: https://logtape.org/manual/adaptors

Commands to add the Bunyan adapter package using various package managers.

```sh
deno add jsr:@logtape/adaptor-bunyan
```

```sh
npm add @logtape/adaptor-bunyan
```

```sh
pnpm add @logtape/adaptor-bunyan
```

```sh
yarn add @logtape/adaptor-bunyan
```

```sh
bun add @logtape/adaptor-bunyan
```

--------------------------------

### Use Explicit Setup in Tests

Source: https://logtape.org/manual/testing

Importing from the main package allows using configured LogTape instances in test files.

```typescript
import { test, expect } from "@logtape/testing-vitest";
import { getLogger } from "@logtape/logtape";

test("case", () => {
  getLogger(["my-lib"]).info("Fixture state: {state}.", {
    state: "ready",
  });

  expect(1 + 1).toBe(2);
  // The info log is printed only if this test fails.
});
```

--------------------------------

### Configure LogTape with Fastify

Source: https://logtape.org/manual/integrations

Basic setup for using LogTape as the logging backend for a Fastify application.

```typescript
import { configure, getConsoleSink } from "@logtape/logtape";
import { getLogTapeFastifyLogger } from "@logtape/fastify";
import Fastify from "fastify";

await configure({
  sinks: { console: getConsoleSink() },
  loggers: [
    { category: ["fastify"], sinks: ["console"], lowestLevel: "info" }
  ],
});

const fastify = Fastify({
  loggerInstance: getLogTapeFastifyLogger(),
});

fastify.get("/", async (request, reply) => {
  // Uses LogTape under the hood with request context
  request.log.info("Handling request");
  return { hello: "world" };
});

await fastify.listen({ port: 3000 });
```

--------------------------------

### Traditional library logging with winston

Source: https://logtape.org/comparison

Example of a library forcing a specific logging configuration on the consumer.

```typescript
// In some-library/index.js
import winston from "winston";

const logger = winston.createLogger({
  level: "info",
  format: winston.format.json(),
  transports: [new winston.transports.Console()]
});

export function processData(data) {
  logger.info("Processing data", { size: data.length });
  // ... process data
}
```

--------------------------------

### Configure standard file sink

Source: https://logtape.org/sinks/file

Example of configuring a file sink with custom buffering and non-blocking settings.

```typescript
// @noErrors: 2345
import { getFileSink } from "@logtape/file";
import { configure } from "@logtape/logtape";

await configure({
  sinks: {
    file: getFileSink("my-app.log", {
      lazy: true,
      bufferSize: 8192,
      flushInterval: 5000,
      nonBlocking: true,
    }),
  },
  // Omitted for brevity
});
```

--------------------------------

### Install OpenTelemetry sink package

Source: https://logtape.org/sinks/otel

Commands to add the @logtape/otel package using various package managers.

```sh
deno add jsr:@logtape/otel
```

```sh
npm add @logtape/otel
```

```sh
pnpm add @logtape/otel
```

```sh
yarn add @logtape/otel
```

```sh
bun add @logtape/otel
```

--------------------------------

### Configure pretty formatter

Source: https://logtape.org/manual/formatters

Example of integrating the prettyFormatter into the LogTape configuration for the console sink.

```typescript
import { configure, getConsoleSink  } from "@logtape/logtape";
import { prettyFormatter } from "@logtape/pretty";

await configure({
  sinks: {
    console: getConsoleSink({ formatter: prettyFormatter }),
  },
  loggers: [
    { category: [], sinks: ["console"], lowestLevel: "debug" },
  ],
});
```

--------------------------------

### Install LogTape Fastify package

Source: https://logtape.org/manual/integrations

Commands to add the @logtape/fastify package using various package managers.

```Deno
deno add jsr:@logtape/fastify
```

```npm
npm add @logtape/fastify
```

```pnpm
pnpm add @logtape/fastify
```

```Yarn
yarn add @logtape/fastify
```

```Bun
bun add @logtape/fastify
```

--------------------------------

### Configure shared LogTape preload module

Source: https://logtape.org/manual/testing

Define a shared setup module and preload it for the test run to avoid per-file configuration.

```typescript
import { AsyncLocalStorage } from "node:async_hooks";
import { configure } from "@logtape/logtape";

await configure({
  contextLocalStorage: new AsyncLocalStorage(),
  sinks: {},
  loggers: [
    { category: ["logtape", "meta"], sinks: [] },
  ],
});
```

```bash
deno test --preload ./test/setup-logtape.ts
```

```typescript
import { test } from "@logtape/testing-deno";
import { getLogger } from "@logtape/logtape";

test("case", () => {
  getLogger(["my-lib"]).info("Fixture state: {state}.", {
    state: "ready",
  });

  // Run assertions.  The info log is printed only if this test fails.
});
```

--------------------------------

### Configure shared LogTape preload module

Source: https://logtape.org/manual/testing

Define a shared setup module and preload it for the test run to avoid per-file configuration.

```typescript
import { AsyncLocalStorage } from "node:async_hooks";
import { configure } from "@logtape/logtape";

await configure({
  contextLocalStorage: new AsyncLocalStorage(),
  sinks: {},
  loggers: [
    { category: ["logtape", "meta"], sinks: [] },
  ],
});
```

```bash
bun test --preload ./test/setup-logtape.ts
```

```typescript
import { test } from "@logtape/testing-bun";
import { getLogger } from "@logtape/logtape";

test("case", () => {
  getLogger(["my-lib"]).info("Fixture state: {state}.", {
    state: "ready",
  });

  // Run assertions.  The info log is printed only if this test fails.
});
```

--------------------------------

### Add prepare script to package.json

Source: https://logtape.org/manual/llm

Configure the prepare script in your package.json to ensure skills-npm runs during installation.

```json
{
  "scripts": {
    "prepare": "skills-npm"
  }
}
```

--------------------------------

### Configure context local storage

Source: https://logtape.org/manual/categories

Required setup for withCategoryPrefix to function, using AsyncLocalStorage from node:async_hooks.

```typescript
// @noErrors: 2307
import { AsyncLocalStorage } from "node:async_hooks";
import { configure } from "@logtape/logtape";

await configure({
  // ... other settings ...
  // ---cut-start---
  sinks: {},
  loggers: [],
  // ---cut-end---
  contextLocalStorage: new AsyncLocalStorage(),
});
```

--------------------------------

### Define Sinks in Configuration

Source: https://logtape.org/manual/config

Example structure for defining console and file sinks within a configuration object.

```json
{
  "sinks": {
    "console": {
      "type": "#console()"
    },
    "file": {
      "type": "@logtape/file#getFileSink()",
      "path": "/var/log/app.log"
    }
  }
}
```

--------------------------------

### Pretty formatter output example

Source: https://logtape.org/manual/formatters

Visual representation of how log records appear when using the pretty formatter.

```ansi
✨ [4m[38;2;52;211;153minfo[0m    [2m[3m[38;2;100;116;139mlogtape·meta[0m         [2m[38;2;148;163;184mLogTape loggers are configured.  Note that LogTape itself uses the
                                meta logger, which has category [0m[ [32m'logtape'[39m, [32m'meta'[39m ][2m[38;2;148;163;184m.  The meta
                                logger purposes to log internal errors such as sink exceptions.  If
                                you are seeing this message, the meta logger is automatically
                                configured.  It's recommended to configure the meta logger with a
                                separate sink so that you can easily notice if logging itself fails
                                or is misconfigured.  To turn off this message, configure the meta
                                logger with higher log levels than [0m[32m'info'[39m[2m[38;2;148;163;184m.  See also
                                <https://logtape.org/manual/categories#meta-logger>.[0m
🔍 [4m[38;2;167;139;250mtrace[0m   [2m[3m[38;2;100;116;139mmyapp·module[0m         [2m[38;2;148;163;184mThis is a trace log.[0m
🐛 [4m[38;2;96;165;250mdebug[0m   [2m[3m[38;2;100;116;139mmyapp·module[0m         [2m[38;2;148;163;184mThis is a debug log with value: [0m{ foo: [33m123[39m }[2m[38;2;148;163;184m[0m
✨ [4m[38;2;52;211;153minfo[0m    [2m[3m[38;2;100;116;139mmyapp[0m                [2m[38;2;148;163;184mThis is a very long informational log[0m
⚡ [4m[38;2;251;191;36mwarning[0m [2m[3m[38;2;100;116;139mmyapp[0m                [2m[38;2;148;163;184mThis is a warning.[0m
❌ [4m[38;2;248;113;113merror[0m   [2m[3m[38;2;100;116;139mmyapp·module[0m         [2m[38;2;148;163;184mThis is an error with exception: [0mError: This is an exception.[2m[38;2;148;163;184m
                                    at file:///tmp/test.ts:23:10[2m[38;2;148;163;184m[0m
💀 [4m[38;2;220;38;38mfatal[0m   [2m[3m[38;2;100;116;139mmyapp[0m                [2m[38;2;148;163;184mThis is a fatal error.[0m
```

--------------------------------

### Install @logtape/syslog package

Source: https://logtape.org/sinks/syslog

Commands to add the syslog package to your project using various package managers.

```sh
deno add jsr:@logtape/syslog
```

```sh
npm add @logtape/syslog
```

```sh
pnpm add @logtape/syslog
```

```sh
yarn add @logtape/syslog
```

```sh
bun add @logtape/syslog
```

--------------------------------

### Install LogTape Koa middleware

Source: https://logtape.org/manual/integrations

Commands to add the @logtape/koa package using various package managers.

```sh
deno add jsr:@logtape/koa
```

```sh
npm add @logtape/koa
```

```sh
pnpm add @logtape/koa
```

```sh
yarn add @logtape/koa
```

```sh
bun add @logtape/koa
```

--------------------------------

### Configure CloudWatch Logs sink

Source: https://logtape.org/sinks/cloudwatch-logs

Basic setup using getCloudWatchLogsSink with log group, stream, and region parameters.

```typescript
import { configure } from "@logtape/logtape";
import { getCloudWatchLogsSink } from "@logtape/cloudwatch-logs";

await configure({
  sinks: {
    cloudwatch: getCloudWatchLogsSink({
      logGroupName: "/aws/lambda/my-function",
      logStreamName: "my-stream",
      region: "us-east-1",
    }),
  },
  loggers: [
    { category: [], sinks: ["cloudwatch"], lowestLevel: "info" },
  ],
});
```

--------------------------------

### Configure LogTape for tests

Source: https://logtape.org/manual/testing

Defines a reusable setup function for LogTape to be called at the top level of test files.

```typescript
import { AsyncLocalStorage } from "node:async_hooks";
import { configure } from "@logtape/logtape";

let configured = false;

export async function setupLogTape(): Promise<void> {
  if (configured) return;
  configured = true;

  await configure({
    contextLocalStorage: new AsyncLocalStorage(),
    sinks: {},
    loggers: [
      { category: ["logtape", "meta"], sinks: [] },
    ],
  });
}
```

--------------------------------

### Example JSON Log Record

Source: https://logtape.org/sinks/cloudwatch-logs

A sample log record formatted as a JSON object for CloudWatch Logs.

```json
{
  "@timestamp": "2023-12-01T10:30:00.000Z",
  "level": "ERROR",
  "logger": "api.auth",
  "message": "Failed login attempt for user {\"email\":\"user@example.com\"}",
  "properties": {
    "ip": "192.168.1.1",
    "userAgent": "Mozilla/5.0...",
    "attempts": 3
  }
}
```

--------------------------------

### Install LogTape Config Package

Source: https://logtape.org/manual/config

Commands to add the @logtape/config package to your project using various package managers.

```sh
deno add jsr:@logtape/config
```

```sh
npm add @logtape/config
```

```sh
pnpm add @logtape/config
```

```sh
yarn add @logtape/config
```

```sh
bun add @logtape/config
```

--------------------------------

### Install LogTape Lint package

Source: https://logtape.org/lint

Commands to add the @logtape/lint package to your project using different package managers.

```sh
deno add jsr:@logtape/lint
```

```sh
npm add --save-dev @logtape/lint
```

```sh
pnpm add --save-dev @logtape/lint
```

```sh
yarn add --dev @logtape/lint
```

```sh
bun add --dev @logtape/lint
```

--------------------------------

### Manually setting up Cursor skills

Source: https://logtape.org/manual/llm

Copy the skill directory into the project's .cursor/skills folder.

```bash
mkdir -p .cursor/skills
cp -r node_modules/@logtape/logtape/skills/logtape .cursor/skills/logtape
```

--------------------------------

### Incorrect Code Examples

Source: https://logtape.org/lint/no-message-interpolation

Examples that trigger the no-message-interpolation lint error.

```typescript
import { getLogger } from "@logtape/logtape";
const logger = getLogger(["my-app"]);

logger.info(`User ${userId} logged in.`);       // ← error
logger.error(`Request ${reqId} failed.`);       // ← error
logger.debug(`Processing ${items.length} items.`); // ← error
```

--------------------------------

### Configure Windows Event Log sink

Source: https://logtape.org/sinks/windows-eventlog

Example of initializing the Windows Event Log sink within the LogTape configuration.

```typescript
import { configure } from "@logtape/logtape";
import { getWindowsEventLogSink } from "@logtape/windows-eventlog";

await configure({
  sinks: {
    eventlog: getWindowsEventLogSink({
      sourceName: "MyApplication",
    }),
  },
  loggers: [
    { category: [], sinks: ["eventlog"], lowestLevel: "info" },
  ],
});
```

--------------------------------

### Incorrect usage example

Source: https://logtape.org/lint/no-unawaited-log

An example of an unawaited log call that triggers the lint error.

```typescript
import { getLogger } from "@logtape/logtape";
const logger = getLogger(["my-app"]);

async function handler() {
  logger.debug("Data: {d}.", async () => ({  // ← error
    d: await fetchData(),
  }));
}
```

--------------------------------

### Configuring postinstall script

Source: https://logtape.org/manual/llm

Automate skill export by adding a postinstall script to package.json.

```json
{
  "scripts": {
    "postinstall": "agents export --target claude"
  }
}
```

--------------------------------

### Correct usage examples

Source: https://logtape.org/lint/prefer-lazy-evaluation

Shows how to wrap property objects in arrow functions to satisfy the rule, and notes that static values are permitted.

```typescript
import { getLogger } from "@logtape/logtape";
const logger = getLogger(["my-app"]);

// Wrap the object in an arrow function:
logger.debug("Fetched data: {data}.", () => ({ data: fetchData() }));
logger.debug("Value: {x}.", () => ({ x: compute() }));

// Plain property values without calls are fine:
logger.info("Hello {name}.", { name: "world" });
logger.info("Count: {n}.", { n: items.length });
```

--------------------------------

### Configure LogTape via dedicated setup file

Source: https://logtape.org/manual/config

Create a dedicated configuration file and import it first in the application entry point to ensure synchronous initialization.

```typescript
import { configureSync, getConsoleSink } from "@logtape/logtape";

configureSync({
  sinks: {
    console: getConsoleSink(),
  },
  loggers: [
    {
      category: "my-app",
      lowestLevel: "debug",
      sinks: ["console"],
    },
  ],
});
```

```typescript
// Configuration must be imported first!
import "./setup";

import { App } from "./App";
// ... rest of your application
```

--------------------------------

### Manually setting up Claude Code skills

Source: https://logtape.org/manual/llm

Copy the skill directory into the project's .claude/skills folder.

```bash
mkdir -p .claude/skills
cp -r node_modules/@logtape/logtape/skills/logtape .claude/skills/logtape
```

--------------------------------

### Default text formatter output

Source: https://logtape.org/manual/formatters

Example output format for the defaultTextFormatter.

```text
2023-11-14 22:13:20.000 +00:00 [INF] category·subcategory: Hello, world!
```

--------------------------------

### Configure library logging with LogTape

Source: https://logtape.org/manual/library

Demonstrates setting up console and file sinks, defining log levels, and applying filters for specific library categories.

```typescript
// @noErrors: 2307
import { getFileSink } from "@logtape/file";
import { configure, getConsoleSink } from "@logtape/logtape";
import { Database } from "my-awesome-lib";

await configure({
  sinks: {
    console: getConsoleSink(),
    file: getFileSink("app.log")
  },
  filters: {
    excludeDebug: (record) => record.level !== "debug"
  },
  loggers: [
    {
      category: ["my-awesome-lib"],
      lowestLevel: "info",
      sinks: ["console", "file"]
    },
    {
      category: ["my-awesome-lib", "database"],
      lowestLevel: "debug",
      sinks: ["file"],
      filters: ["excludeDebug"]
    }
  ]
});

const db = new Database("localhost", 5432, "user");
db.connect();
db.query("SELECT * FROM users");
```

--------------------------------

### Log with structured data

Source: https://logtape.org/sinks/syslog

Example of logging a message with properties that will be included as structured data.

```typescript
import { configure, getLogger } from "@logtape/logtape";
import { getSyslogSink } from "@logtape/syslog";

await configure({
  sinks: {
    syslog: getSyslogSink({
      includeStructuredData: true,
      structuredDataId: "myapp@12345",
    }),
  },
  loggers: [
    { category: [], sinks: ["syslog"], lowestLevel: "debug" },
  ],
});

const logger = getLogger();
logger.info("User login successful", { userId: 12345, method: "oauth" });
```

--------------------------------

### Implement a universal library with LogTape

Source: https://logtape.org/comparison

Demonstrates using LogTape to create a logging-enabled library that functions consistently across all major JavaScript runtimes.

```typescript
// Works in Node.js, Deno, Bun, browsers, and edge functions
import { getLogger } from "@logtape/logtape";

const logger = getLogger(["my-universal-lib"]);

export function apiCall(url: string) {
  logger.debug("Making API call to {url}", { url });

  // Use appropriate fetch implementation for the runtime
  return fetch(url).then(response => {
    logger.info("API call completed with status {status}", {
      status: response.status
    });
    return response;
  });
}
```

--------------------------------

### Basic Express Integration

Source: https://logtape.org/manual/integrations

Standard setup for using LogTape middleware in an Express application.

```typescript
import { configure, getConsoleSink } from "@logtape/logtape";
import { expressLogger } from "@logtape/express";
import express from "express";

await configure({
  sinks: { console: getConsoleSink() },
  loggers: [
    { category: ["express"], sinks: ["console"], lowestLevel: "info" }
  ],
});

const app = express();
app.use(expressLogger());

app.get("/", (req, res) => {
  res.json({ hello: "world" });
});

app.listen(3000);
```

--------------------------------

### logfmt formatter output

Source: https://logtape.org/manual/formatters

Example output format for the logfmtFormatter, producing space-delimited key-value pairs.

```logfmt
time=2023-11-14T22:13:20.000Z level=info logger=my.logger msg="Hello, world!" key=value
```

--------------------------------

### Use Autoload Entry Point

Source: https://logtape.org/manual/testing

Importing from the autoload entry point configures minimal context storage for failure log reporting.

```typescript
import { test, expect } from "@logtape/testing-vitest/autoload";
import { getLogger } from "@logtape/logtape";

test("case", () => {
  getLogger(["my-lib"]).info("Fixture state: {state}.", {
    state: "ready",
  });

  expect(1 + 1).toBe(2);
  // The info log is printed only if this test fails.
});
```

--------------------------------

### Basic Koa integration

Source: https://logtape.org/manual/integrations

Standard setup for using LogTape middleware within a Koa application.

```typescript
import { configure, getConsoleSink } from "@logtape/logtape";
import { koaLogger } from "@logtape/koa";
import Koa from "koa";

await configure({
  sinks: { console: getConsoleSink() },
  loggers: [
    { category: ["koa"], sinks: ["console"], lowestLevel: "info" }
  ],
});

const app = new Koa();
app.use(koaLogger());

app.use((ctx) => {
  ctx.body = { hello: "world" };
});

app.listen(3000);
```

--------------------------------

### Configure LogTape Synchronously

Source: https://logtape.org/manual/config

Use this for synchronous setup. Note that sinks requiring asynchronous disposal, such as stream sinks, cannot be used with this method.

```typescript
import { configureSync, getConsoleSink } from "@logtape/logtape";

configureSync({
  sinks: {
    console: getConsoleSink(),
  },
  loggers: [
    {
      category: "my-app",
      lowestLevel: "info",
      sinks: ["console"],
    },
  ],
});
```
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