evlog

→ evlog Documentation

What create-faster adds

The setup varies by stack. Each gets the idiomatic evlog integration for its framework.

Next.js

Files added:

src/
├── lib/
│   └── evlog.ts            # createEvlog + createInstrumentation
└── instrumentation.ts      # defineNodeInstrumentation (Node runtime gate)

Modified files:

• src/proxy.ts - Returns via evlogMiddleware() for request-id and timing correlation

evlog.ts

Factory exports for request-scoped logging and server instrumentation:

import { createEvlog } from 'evlog/next';
import { createInstrumentation } from 'evlog/next/instrumentation';

export const { withEvlog, useLogger, log, createError } = createEvlog({
  service: 'my-app',
});

export const { register, onRequestError } = createInstrumentation({
  service: 'my-app',
});

• withEvlog() wraps route handlers to emit wide events on request completion
• useLogger() provides request-scoped log.set() for progressive context
• createError() throws structured errors with why, fix, link fields

instrumentation.ts

Gates evlog initialization to the Node.js runtime so Edge bundles stay clean:

import { defineNodeInstrumentation } from 'evlog/next/instrumentation';

export const { register, onRequestError } = defineNodeInstrumentation(() => import('./lib/evlog'));

proxy.ts

When evlog is selected, proxy.ts returns via evlogMiddleware() which sets x-request-id and x-evlog-start headers for timing correlation across the middleware-to-handler chain. Composes cleanly with Better Auth session resolution.

Hono

Modified files:

• src/app.ts - Adds initLogger, evlog() middleware, typed variables, and structured error handler

import { initLogger, parseError } from 'evlog';
import { evlog, type EvlogVariables } from 'evlog/hono';

initLogger({
  env: { service: 'my-api' },
});

const app = new Hono<EvlogVariables>();

app.use(evlog());

Replaces the default hono/logger middleware. The EvlogVariables type gives typed access to c.get('log') in route handlers.

The error handler uses parseError() for structured JSON responses with why and fix fields.

TanStack Start

Files added:

nitro.config.ts             # evlog/nitro/v3 module registration

Modified files:

• src/routes/__root.tsx - Adds evlogErrorHandler server middleware

nitro.config.ts

Registers the evlog Nitro v3 module with async context for request-scoped logging:

import { defineConfig } from 'nitro';
import evlog from 'evlog/nitro/v3';

export default defineConfig({
  experimental: {
    asyncContext: true,
  },
  modules: [
    evlog({
      env: { service: 'my-app' },
    }),
  ],
});

__root.tsx

Wires evlogErrorHandler as a TanStack Start server middleware to preserve structured error data fields (why, fix, link) in responses:

import { createMiddleware } from '@tanstack/react-start'
import { evlogErrorHandler } from 'evlog/nitro/v3'

export const Route = createRootRoute({
  server: {
    middleware: [createMiddleware().server(evlogErrorHandler)],
  },
  // ...
})

Node

Modified files:

• src/index.ts - Adds initLogger with service name

import { initLogger, log } from 'evlog';

initLogger({
  env: { service: 'my-worker' },
});

log.info({ action: 'startup' });

For standalone scripts and workers, use createLogger() and createRequestLogger() from evlog for manual wide events with log.set() / log.emit().