review-logging-patterns

name	review-logging-patterns
description	Review code for logging patterns and suggest evlog adoption. Optionally use @evlog/cli (`evlog init` to wire evlog, `evlog agents` to write the conventions into AGENTS.md, `evlog map` to score entry-point coverage, `--baseline` to gate regressions in CI) on Nuxt, Nitro, Next.js, TanStack Start, and Hono. Guides setup on those plus SvelteKit, React Router, NestJS, Express, Fastify, Elysia, oRPC, Cloudflare Workers, AWS Lambda, Astro, and standalone TypeScript. Detects console.log spam, unstructured errors, and missing context. Covers wide events, structured errors, drain adapters (Axiom, OTLP, HyperDX, PostHog, Sentry, Better Stack, Datadog, Loki, ClickHouse, NuxtHub, Memory), sampling, enrichers, and AI SDK integration.
license	MIT
metadata	{"author":"HugoRCD","version":"0.9"}

Review logging patterns

Review and improve logging patterns in TypeScript/JavaScript codebases. Transform scattered console.logs into structured wide events and convert generic errors into self-documenting structured errors.

When to Use

• Setting up evlog in a new or existing project (any supported framework)
• Reviewing code for logging best practices
• Converting console.log statements to structured logging
• Improving error handling with better context
• Configuring log draining, sampling, or enrichment

Quick Reference

Working on...	Resource
Setup (CLI)	evlog init — wire evlog into the project
Project conventions (CLI)	evlog agents — write the evlog block into the project's AGENTS.md
Coverage map (CLI)	evlog map — score dark entry points
CI gating (CLI)	evlog map --min-score / --baseline — gate regressions
Wide events patterns	references/wide-events.md
Error handling	references/structured-errors.md
Code review checklist	references/code-review.md
Drain pipeline	references/drain-pipeline.md
Audit logs	build-audit-logs skill + docs

Audit logs

For security-sensitive actions (auth, billing, admin, data export), use evlog's audit layer: a typed audit field on wide events, not a parallel logger. See the build-audit-logs skill for end-to-end setup (log.audit, withAudit, denials, auditEnricher, auditOnly, signed, mockAudit).

log.audit({
  action: 'invoice.refund',
  actor: { type: 'user', id: user.id },
  target: { type: 'invoice', id: invoice.id },
  outcome: 'success',
})

Docs: https://www.evlog.dev/use-cases/audit/overview

Installation

npm install evlog

Use the CLI (recommended on Nuxt, Nitro, Next.js, TanStack Start, Hono)

@evlog/cli is a separate package from evlog, early but worth trying. It reads the project on disk (no traffic, no config). On the five supported frameworks it covers the whole loop: wire evlog in (init), score coverage (map), lock the score in CI (--min-score, --baseline). If the CLI is unavailable, the framework has no adapter yet, or the user declines, continue with the manual sections below; the skill does not depend on it. Ask before installing anything; prefer npx / pnpm dlx for one-shots.

1. Setup: evlog init

On a project that doesn't use evlog yet, prefer init over hand-writing the setup, since it detects the framework, reads what the project already has, and generates config, drains, enrichers, and extras in one pass. It is fully scriptable for agents:

# preview everything without writing (always start here)
npx @evlog/cli init --dry-run --yes

# then apply — flags instead of prompts
npx @evlog/cli init --yes \
  --service my-app \
  --drain fs \
  --prodDrain axiom \
  --extras enrichers,pipeline,sampling \
  --sampling medium

Useful flags: --framework (override detection: nuxt, nitro, next, tanstack-start, hono), --prodDrain (comma-separated: axiom, otlp, posthog, sentry, better-stack, datadog, hyperdx), --extras (enrichers, pipeline, sampling, vite, error-catalog, audit-catalog, ai, better-auth), --enrichers, --sampling (traffic tier: all, low, medium, high, very-high), --apps (monorepo: which workspace packages), --no-install. Review the --dry-run output with the user before applying. Docs: https://www.evlog.dev/cli/init

2. Score: evlog map

npx @evlog/cli map --no-write
# agents: npx @evlog/cli map --json --no-write

What you get:

• A project score and which entry points are still dark
• FIX FIRST: the three most valuable places to fix
• GOING FURTHER: opportunities (catalogs, audit coverage, AI logging, auth identity) that never cost points
• Per-file inspect: npx @evlog/cli map <file> --no-write shows the shape the handler could take
• Re-run after fixes and watch the score move

Work FIX FIRST in order, keep changes minimal (useLogger(), log.set(), log.audit(), createError({ why, fix })), then re-run with --no-write. Omit --no-write only when the user wants evlog.map.json written.

3. Lock it in CI: --min-score and --baseline

After fixing, propose making the score durable. This is where the CLI earns its keep:

# in CI, after pnpm add -D @evlog/cli (project-local, pinned by the lockfile)
pnpm exec evlog map --min-score 80   # absolute gate: exits 1 below the threshold
pnpm exec evlog map --baseline       # ratchet: exits 1 if this PR made things worse

--baseline compares the fresh scan against the committed evlog.map.json, per entry point and per requirement, so a refactor that instruments one route and breaks another fails even if the total score is unchanged. Disabling a passing check with a comment counts as a regression too. New uninstrumented routes are listed as NEW AND DARK without failing. Workflow: commit evlog.map.json once, add the --baseline run to CI (pnpm add -D @evlog/cli for a pinned version, and ask first), then re-run map without --baseline to accept an intentional change. Docs: https://www.evlog.dev/cli/ci

Early days: adapters and rules are still evolving; expect scores to move between releases. Docs: https://www.evlog.dev/cli/map · Rules: https://www.evlog.dev/cli/rules

---

Framework Setup

Nuxt

// nuxt.config.ts
export default defineNuxtConfig({
  modules: ['evlog/nuxt'],
  evlog: {
    env: { service: 'my-app' },
    include: ['/api/**'],
  },
})

useLogger, log, and parseError are auto-imported. createError is not: a bare one resolves to h3's, which drops why, fix, and link. Import it from evlog.

// server/api/checkout.post.ts — no imports needed
export default defineEventHandler(async (event) => {
  const log = useLogger(event)
  log.set({ user: { id: user.id, plan: user.plan } })
  return { success: true }
})

Drain, enrich, and tail sampling use Nitro hooks in server plugins:

// server/plugins/evlog-drain.ts
import { createAxiomDrain } from 'evlog/axiom'

export default defineNitroPlugin((nitroApp) => {
  nitroApp.hooks.hook('evlog:drain', createAxiomDrain())
})

Client transport (auto-configured Vue plugin):

// nuxt.config.ts
evlog: {
  transport: { enabled: true },  // logs sent to /api/_evlog/ingest
}

Client-side: log, setIdentity, clearIdentity are auto-imported in components.

Next.js

Step 1: Create central config. All exports come from here:

// lib/evlog.ts
import type { DrainContext } from 'evlog'
import { createEvlog } from 'evlog/next'
import { createUserAgentEnricher, createRequestSizeEnricher } from 'evlog/enrichers'
import { createDrainPipeline } from 'evlog/pipeline'

const enrichers = [createUserAgentEnricher(), createRequestSizeEnricher()]
const pipeline = createDrainPipeline<DrainContext>({ batch: { size: 50, intervalMs: 5000 } })
const drain = pipeline(createAxiomDrain({ dataset: 'logs', apiKey: process.env.AXIOM_API_KEY! }))

export const { withEvlog, useLogger, log, createError } = createEvlog({
  service: 'my-app',
  sampling: {
    rates: { info: 10 },
    keep: [{ status: 400 }, { duration: 1000 }],
  },
  routes: {
    '/api/auth/**': { service: 'auth-service' },
    '/api/checkout/**': { service: 'checkout-service' },
  },
  keep: (ctx) => {
    const user = ctx.context.user as { premium?: boolean } | undefined
    if (user?.premium) ctx.shouldKeep = true
  },
  enrich: (ctx) => {
    for (const enricher of enrichers) enricher(ctx)
  },
  drain,
})

Step 2: Wrap route handlers with withEvlog():

// app/api/checkout/route.ts
import { withEvlog, useLogger } from '@/lib/evlog'

export const POST = withEvlog(async (request: Request) => {
  const log = useLogger()  // Zero arguments — uses AsyncLocalStorage
  log.set({ user: { id: 'user_123', plan: 'enterprise' } })
  log.set({ cart: { items: 3, total: 14999 } })
  return Response.json({ success: true })
})

Step 3: Server Actions. Same withEvlog() wrapper:

// app/actions.ts
'use server'
import { withEvlog, useLogger } from '@/lib/evlog'

export const checkout = withEvlog(async (formData: FormData) => {
  const log = useLogger()
  log.set({ action: 'checkout', source: 'server-action' })
  return { success: true }
})

Step 4: Middleware (optional, sets x-request-id + timing headers):

// proxy.ts
import { evlogMiddleware } from 'evlog/next'
export const proxy = evlogMiddleware()
export const config = { matcher: ['/api/:path*'] }

Step 5: Client Provider. Wrap the root layout:

// app/layout.tsx
import { EvlogProvider } from 'evlog/next/client'

export default function Layout({ children }: { children: React.ReactNode }) {
  return (
    <html lang="en">
      <body>
        <EvlogProvider service="my-app" transport={{ enabled: true, endpoint: '/api/evlog/ingest' }}>
          {children}
        </EvlogProvider>
      </body>
    </html>
  )
}

Step 6: Client logging. In any client component:

'use client'
import { log, setIdentity, clearIdentity } from 'evlog/next/client'

setIdentity({ userId: 'usr_123' })
log.info({ action: 'checkout_click' })
clearIdentity()

Step 7 (optional): Instrumentation. Startup plus global onRequestError (SSR/RSC errors outside withEvlog). Use defineNodeInstrumentation(() => import('./lib/evlog')) in root instrumentation.ts to gate Node + cache the import, or write register/onRequestError manually. Both are valid. For custom logic, wrap evlog’s register/onRequestError inside lib/evlog.ts (compose with your own init or metrics), then re-export.

Export createInstrumentation() from lib/evlog.ts alongside createEvlog(). See framework docs for coexistence with lockLogger.

Step 8: Client ingest endpoint. Receives client logs:

// app/api/evlog/ingest/route.ts
import { NextRequest } from 'next/server'

const VALID_LEVELS = ['info', 'error', 'warn', 'debug'] as const

export async function POST(request: NextRequest) {
  const origin = request.headers.get('origin')
  const host = request.headers.get('host')
  if (origin && new URL(origin).host !== host) {
    return Response.json({ error: 'Invalid origin' }, { status: 403 })
  }
  const body = await request.json()
  if (!body?.timestamp || !body?.level || !VALID_LEVELS.includes(body.level)) {
    return Response.json({ error: 'Invalid payload' }, { status: 400 })
  }
  const { service: _, ...sanitized } = body
  console.log('[CLIENT LOG]', JSON.stringify({ ...sanitized, service: 'my-app', source: 'client' }))
  return new Response(null, { status: 204 })
}

SvelteKit

// src/hooks.server.ts
import { initLogger } from 'evlog'
import { createEvlogHooks } from 'evlog/sveltekit'

initLogger({ env: { service: 'my-app' } })

export const { handle, handleError } = createEvlogHooks()

Access the logger via event.locals.log in route handlers or useLogger() from anywhere in the call stack:

// src/routes/api/users/[id]/+server.ts
import { json } from '@sveltejs/kit'

export const GET = ({ locals, params }) => {
  locals.log.set({ user: { id: params.id } })
  return json({ id: params.id })
}

import { useLogger } from 'evlog/sveltekit'

async function findUsers() {
  const log = useLogger()
  log.set({ db: { query: 'SELECT * FROM users' } })
}

Full pipeline with drain, enrich, and tail sampling:

import { createAxiomDrain } from 'evlog/axiom'

export const { handle, handleError } = createEvlogHooks({
  include: ['/api/**'],
  drain: createAxiomDrain(),
  enrich: (ctx) => { ctx.event.region = process.env.FLY_REGION },
  keep: (ctx) => {
    if (ctx.duration && ctx.duration > 2000) ctx.shouldKeep = true
  },
})

Nitro v3

// nitro.config.ts
import { defineConfig } from 'nitro'
import evlog from 'evlog/nitro/v3'

export default defineConfig({
  modules: [evlog({ env: { service: 'my-api' } })],
})

// routes/api/checkout.post.ts
import { defineHandler } from 'nitro/h3'
import { useLogger } from 'evlog/nitro/v3'

export default defineHandler(async (event) => {
  const log = useLogger(event)
  log.set({ action: 'checkout' })
  return { ok: true }
})

TanStack Start

TanStack Start uses Nitro v3. Install evlog and add a nitro.config.ts:

// nitro.config.ts
import { defineConfig } from 'nitro'
import evlog from 'evlog/nitro/v3'

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

Add the error handling middleware to __root.tsx:

// src/routes/__root.tsx
import { createMiddleware } from '@tanstack/react-start'
import { evlogErrorHandler } from 'evlog/nitro/v3'

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

Use useRequest() from nitro/context to access the logger:

import { useRequest } from 'nitro/context'
import type { RequestLogger } from 'evlog'

const req = useRequest()
const log = req.context.log as RequestLogger
log.set({ user: { id: 'user_123' } })

Nitro v2

// nitro.config.ts
import { defineNitroConfig } from 'nitropack/config'
import evlog from 'evlog/nitro'

export default defineNitroConfig({
  modules: [evlog({ env: { service: 'my-api' } })],
})

Import useLogger from evlog/nitro in routes.

NestJS

// src/app.module.ts
import { Module } from '@nestjs/common'
import { EvlogModule } from 'evlog/nestjs'

@Module({
  imports: [EvlogModule.forRoot()],
})
export class AppModule {}

EvlogModule.forRoot() registers a global middleware. Use useLogger() to access the request-scoped logger from any controller or service:

import { useLogger } from 'evlog/nestjs'

async function findUsers() {
  const log = useLogger()
  log.set({ db: { query: 'SELECT * FROM users' } })
}

Full pipeline with drain, enrich, and tail sampling:

import { createAxiomDrain } from 'evlog/axiom'

EvlogModule.forRoot({
  include: ['/api/**'],
  drain: createAxiomDrain(),
  enrich: (ctx) => { ctx.event.region = process.env.FLY_REGION },
  keep: (ctx) => {
    if (ctx.duration && ctx.duration > 2000) ctx.shouldKeep = true
  },
})

For async configuration with NestJS DI, use forRootAsync():

EvlogModule.forRootAsync({
  imports: [ConfigModule],
  inject: [ConfigService],
  useFactory: (config) => ({
    drain: createAxiomDrain({ apiKey: config.get('AXIOM_API_KEY') }),
  }),
})

Express

import express from 'express'
import { initLogger } from 'evlog'
import { evlog, useLogger } from 'evlog/express'

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

const app = express()
app.use(evlog())

app.get('/api/users', (req, res) => {
  req.log.set({ users: { count: 42 } })
  res.json({ users: [] })
})

Use useLogger() to access the logger from anywhere in the call stack without passing req:

import { useLogger } from 'evlog/express'

async function findUsers() {
  const log = useLogger()
  log.set({ db: { query: 'SELECT * FROM users' } })
}

Full pipeline with drain, enrich, and tail sampling:

import { createAxiomDrain } from 'evlog/axiom'

app.use(evlog({
  include: ['/api/**'],
  drain: createAxiomDrain(),
  enrich: (ctx) => { ctx.event.region = process.env.FLY_REGION },
  keep: (ctx) => {
    if (ctx.duration && ctx.duration > 2000) ctx.shouldKeep = true
  },
}))

Hono

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

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

const app = new Hono<EvlogVariables>()
app.use(evlog())

app.get('/api/users', (c) => {
  const log = c.get('log')
  log.set({ users: { count: 42 } })
  return c.json({ users: [] })
})

Access the logger via c.get('log') in handlers. Use useLogger() from evlog/hono in the layers underneath (services, repositories) where c is not in hand. Both return the same logger:

import { useLogger } from 'evlog/hono'

async function findUsers() {
  const log = useLogger()
  log.set({ db: { query: 'SELECT * FROM users' } })
}

On Cloudflare Workers, useLogger() needs the nodejs_compat (or nodejs_als) compatibility flag; c.get('log') works with or without it.

Structured errors: throw createError(), then in app.onError use parseError() and pass parsed.status as ContentfulStatusCode to c.json() (Hono types the status argument as ContentfulStatusCode, not number).

import { createError, parseError } from 'evlog'
import type { ContentfulStatusCode } from 'hono/utils/http-status'

app.onError((error, c) => {
  c.get('log').error(error)
  const parsed = parseError(error)
  return c.json(
    { message: parsed.message, why: parsed.why, fix: parsed.fix, link: parsed.link },
    parsed.status as ContentfulStatusCode,
  )
})

Full pipeline with drain, enrich, and tail sampling:

import { createAxiomDrain } from 'evlog/axiom'

app.use(evlog({
  include: ['/api/**'],
  drain: createAxiomDrain(),
  enrich: (ctx) => { ctx.event.region = process.env.FLY_REGION },
  keep: (ctx) => {
    if (ctx.duration && ctx.duration > 2000) ctx.shouldKeep = true
  },
}))

Fastify

import Fastify from 'fastify'
import { initLogger } from 'evlog'
import { evlog, useLogger } from 'evlog/fastify'

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

const app = Fastify({ logger: false })
await app.register(evlog)

app.get('/api/users', async (request) => {
  request.log.set({ users: { count: 42 } })
  return { users: [] }
})

request.log is the evlog wide-event logger (shadows Fastify's built-in pino logger on the request). Fastify's pino logger remains accessible via fastify.log.

Use useLogger() to access the logger from anywhere in the call stack without passing request:

import { useLogger } from 'evlog/fastify'

async function findUsers() {
  const log = useLogger()
  log.set({ db: { query: 'SELECT * FROM users' } })
}

Full pipeline with drain, enrich, and tail sampling:

import { createAxiomDrain } from 'evlog/axiom'

await app.register(evlog, {
  include: ['/api/**'],
  drain: createAxiomDrain(),
  enrich: (ctx) => { ctx.event.region = process.env.FLY_REGION },
  keep: (ctx) => {
    if (ctx.duration && ctx.duration > 2000) ctx.shouldKeep = true
  },
})

Elysia

import { Elysia } from 'elysia'
import { initLogger } from 'evlog'
import { evlog, useLogger } from 'evlog/elysia'

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

const app = new Elysia()
  .use(evlog())
  .get('/api/users', ({ log }) => {
    log.set({ users: { count: 42 } })
    return { users: [] }
  })
  .listen(3000)

Use useLogger() to access the logger from anywhere in the call stack:

import { useLogger } from 'evlog/elysia'

async function findUsers() {
  const log = useLogger()
  log.set({ db: { query: 'SELECT * FROM users' } })
}

Full pipeline with drain, enrich, and tail sampling:

import { createAxiomDrain } from 'evlog/axiom'

app.use(evlog({
  include: ['/api/**'],
  drain: createAxiomDrain(),
  enrich: (ctx) => { ctx.event.region = process.env.FLY_REGION },
  keep: (ctx) => {
    if (ctx.duration && ctx.duration > 2000) ctx.shouldKeep = true
  },
}))

React Router

// react-router.config.ts
import type { Config } from '@react-router/dev/config'

export default {
  future: {
    v8_middleware: true,
  },
} satisfies Config

// app/root.tsx
import { initLogger } from 'evlog'
import { evlog } from 'evlog/react-router'

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

export const middleware: Route.MiddlewareFunction[] = [
  evlog(),
]

Access the logger via context.get(loggerContext) in loaders and actions:

// app/routes/api.users.$id.tsx
import { loggerContext } from 'evlog/react-router'

export async function loader({ params, context }: Route.LoaderArgs) {
  const log = context.get(loggerContext)
  log.set({ user: { id: params.id } })
  return { users: [] }
}

Use useLogger() to access the logger from anywhere in the call stack without passing context:

import { useLogger } from 'evlog/react-router'

async function findUsers() {
  const log = useLogger()
  log.set({ db: { query: 'SELECT * FROM users' } })
}

Full pipeline with drain, enrich, and tail sampling:

import { createAxiomDrain } from 'evlog/axiom'

export const middleware: Route.MiddlewareFunction[] = [
  evlog({
    include: ['/api/**'],
    drain: createAxiomDrain(),
    enrich: (ctx) => { ctx.event.region = process.env.FLY_REGION },
    keep: (ctx) => {
      if (ctx.duration && ctx.duration > 2000) ctx.shouldKeep = true
    },
  }),
]

oRPC

import { os } from '@orpc/server'
import { RPCHandler } from '@orpc/server/fetch'
import { initLogger } from 'evlog'
import { evlog, withEvlog, type EvlogOrpcContext } from 'evlog/orpc'

initLogger({ env: { service: 'my-rpc' } })

const base = os.$context<EvlogOrpcContext>().use(evlog())

const router = {
  ping: base.handler(({ context }) => {
    context.log.set({ pinged: true })
    return { ok: true }
  }),
}

const handler = withEvlog(new RPCHandler(router))

export default async function fetch(request: Request) {
  const { matched, response } = await handler.handle(request, { prefix: '/rpc' })
  return matched ? response : new Response('Not Found', { status: 404 })
}

withEvlog() wraps the handler so each matched request emits one wide event; os.use(evlog()) exposes context.log on every procedure that descends from base and tags the wide event with operation (the procedure path joined with .).

Use useLogger() to access the logger from utility modules:

import { useLogger } from 'evlog/orpc'

async function chargeCard(amount: number) {
  const log = useLogger()
  log.set({ payment: { amount } })
}

Full pipeline with drain, enrich, and tail sampling:

import { createAxiomDrain } from 'evlog/axiom'

const handler = withEvlog(new RPCHandler(router), {
  include: ['/rpc/**'],
  drain: createAxiomDrain(),
  enrich: (ctx) => { ctx.event.region = process.env.FLY_REGION },
  keep: (ctx) => {
    if (ctx.duration && ctx.duration > 2000) ctx.shouldKeep = true
  },
})

Cloudflare Workers

import { initWorkersLogger, withEvlog } from 'evlog/workers'

initWorkersLogger({ env: { service: 'edge-api' } })

export default withEvlog(async (request, _env, _ctx, log) => {
  log.set({ action: 'handle_request' })
  return Response.json({ ok: true })
})

withEvlog emits one wide event per request when the handler returns, with no manual log.emit(). Async drains are registered with waitUntil so they survive the response; streaming responses defer the emit until the body completes. requestId comes from x-request-id (fallback cf-ray); method, path, cf-ray, traceparent, and the safe subset of request.cf are captured automatically. It accepts the same options (drain, enrich, keep, include, exclude, routes) as every other integration. For manual control (scheduled handlers, queues), createWorkersLogger(request) + log.emit() remains available. No ALS-based useLogger() on Workers, so pass log explicitly.

AWS Lambda

Lambda has no HTTP middleware lifecycle, so evlog behaves like standalone TypeScript, with one critical rule: one logger per invocation, never a shared module-level logger (Lambda reuses execution environments, so a shared instance leaks fields between invocations).

import { initLogger, createLogger } from 'evlog'

initLogger({ env: { service: 'my-fn' } })  // once at module load (cold start)

export async function handler(event: SQSEvent) {
  for (const record of event.Records) {
    const log = createLogger({ messageId: record.messageId })
    try {
      log.set({ queue: { source: record.eventSourceARN } })
      await processMessage(record)
    } catch (error) {
      log.error(error as Error)
      throw error
    } finally {
      log.emit()
    }
  }
}

Astro

// src/middleware.ts
import { defineMiddleware } from 'astro:middleware'
import { initLogger, createRequestLogger } from 'evlog'

initLogger({ env: { service: 'my-astro-app' } })

export const onRequest = defineMiddleware(async ({ request, locals }, next) => {
  const url = new URL(request.url)
  const log = createRequestLogger({ method: request.method, path: url.pathname })
  locals.log = log

  try {
    const response = await next()
    log.emit()
    return response
  } catch (error) {
    log.error(error instanceof Error ? error : new Error(String(error)))
    log.emit()
    throw error
  }
})

Type locals.log in src/env.d.ts (interface Locals { log: RequestLogger }). Pair with the Vite plugin (below) for auto-imports and build-time DX.

Vite Plugin (any Vite-based framework)

For any Vite-based project (SvelteKit, Astro, SolidStart, React+Vite, etc.), use the Vite plugin for auto-init, auto-imports, and build-time features:

// vite.config.ts
import evlog from 'evlog/vite'

export default defineConfig({
  plugins: [
    evlog({
      service: 'my-app',
      autoImports: true,           // auto-import log, createEvlogError, parseError
      strip: ['debug'],            // remove log.debug() in production
      sourceLocation: true,        // inject file:line in dev + prod
      client: {                    // client-side logging
        transport: { endpoint: '/api/logs' },
      },
    }),
  ],
})

Server-side middleware (drain, enrich, keep, routes) is still configured in the framework integration (e.g., evlog() middleware for Hono/Express/SvelteKit). The Vite plugin handles build-time DX only.

Standalone TypeScript

import { initLogger, createRequestLogger } from 'evlog'

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

const log = createRequestLogger({ jobId: job.id })
log.set({ source: job.source, recordsSynced: 150 })
log.emit()  // Manual emit required in standalone

---

Configuration Options

All options work in Nuxt (evlog key), Nitro (passed to evlog()), Next.js (createEvlog()), and standalone (initLogger()).

Option	Type	Default	Description
env.service / service	string	'app'	Service name in logs
enabled	boolean	true	Global toggle (no-ops when false)
pretty	boolean	true in dev	Pretty tree format vs JSON
silent	boolean	false	Suppress console output. Events still go to drains
include	string[]	All routes	Route glob patterns to log
exclude	string[]	None	Route patterns to exclude (takes precedence)
routes	Record<string, { service }>	--	Route-specific service names
minLevel	'debug' | 'info' | 'warn' | 'error'	'debug'	Hard threshold for the global log API and client log (not request wide events). Use sampling.rates for probabilistic volume on requests
sampling.rates	object	--	Head sampling: { info: 10, warn: 50 } (0-100%)
sampling.keep	array	--	Tail sampling: [{ status: 400 }, { duration: 1000 }]
drain	(ctx) => void	--	Drain callback (Next.js, standalone)
enrich	(ctx) => void

Nitro Hooks (Nuxt, Nitro v2/v3)

Hook	When	Use
evlog:drain	After enrichment	Send events to external services
evlog:enrich	After emit, before drain	Add derived context
evlog:emit:keep	During emit	Custom tail sampling logic
close	Server shutdown	Flush drain pipeline buffers

---

Drain Adapters

Adapter	Import	Env Vars
Axiom	evlog/axiom	AXIOM_API_KEY, AXIOM_DATASET
OTLP	evlog/otlp	OTLP_ENDPOINT (or OTEL_EXPORTER_OTLP_ENDPOINT)
HyperDX	evlog/hyperdx	HYPERDX_API_KEY (optional HYPERDX_OTLP_ENDPOINT; defaults to https://in-otel.hyperdx.io)
PostHog	evlog/posthog	POSTHOG_API_KEY, POSTHOG_HOST
Sentry	evlog/sentry	SENTRY_DSN
Better Stack	evlog/better-stack	BETTER_STACK_API_KEY
Datadog	evlog/datadog	DD_API_KEY or DATADOG_API_KEY, optional DD_SITE / DATADOG_LOGS_URL
Grafana Loki	evlog/loki	LOKI_ENDPOINT, optional LOKI_API_KEY + LOKI_USER (Grafana Cloud) or LOKI_TENANT_ID (multi-tenant)
ClickHouse	evlog/clickhouse	CLICKHOUSE_ENDPOINT, optional CLICKHOUSE_USER / CLICKHOUSE_PASSWORD / CLICKHOUSE_DATABASE / CLICKHOUSE_TABLE
File System	evlog/fs	None (local file system)
Memory	evlog/memory	None (in-process ring buffer; optional EVLOG_MEMORY_STORE, EVLOG_MEMORY_MAX_EVENTS). Read back with readMemoryLogs() — ideal for dev-only log endpoints agents can query
NuxtHub	(separate package, Nuxt module)

Use canonical env var names (e.g. AXIOM_API_KEY, BETTER_STACK_API_KEY), and the same names work in every framework.

Setup pattern per framework:

// Nuxt/Nitro: server/plugins/evlog-drain.ts
import { createAxiomDrain } from 'evlog/axiom'
export default defineNitroPlugin((nitroApp) => {
  nitroApp.hooks.hook('evlog:drain', createAxiomDrain())
})

// Hono / Express / Elysia: pass drain in middleware options
import { createAxiomDrain } from 'evlog/axiom'
app.use(evlog({ drain: createAxiomDrain() }))

// Fastify: pass drain in plugin options
import { createAxiomDrain } from 'evlog/axiom'
await app.register(evlog, { drain: createAxiomDrain() })

// NestJS: pass drain in module options
import { createAxiomDrain } from 'evlog/axiom'
EvlogModule.forRoot({ drain: createAxiomDrain() })

// Next.js: pass drain to createEvlog()
import { createAxiomDrain } from 'evlog/axiom'
import { createDrainPipeline } from 'evlog/pipeline'
const pipeline = createDrainPipeline<DrainContext>({ batch: { size: 50 } })
const drain = pipeline(createAxiomDrain())
// then: createEvlog({ ..., drain })

// Standalone: pass drain to initLogger()
initLogger({ env: { service: 'my-app' }, drain: createAxiomDrain() })

See references/drain-pipeline.md for batching, retry, and buffer overflow config.

---

Enrichers

Built-in: createUserAgentEnricher(), createGeoEnricher(), createRequestSizeEnricher(), createTraceContextEnricher(), all from evlog/enrichers. Each accepts { overwrite?: boolean } (default false). Use createDefaultEnrichers() to compose all four in one call:

import { createDefaultEnrichers } from 'evlog/enrichers'
app.use(evlog({ enrich: createDefaultEnrichers() }))

// Nuxt/Nitro: server/plugins/evlog-enrich.ts
import { createUserAgentEnricher, createGeoEnricher } from 'evlog/enrichers'
export default defineNitroPlugin((nitroApp) => {
  const enrichers = [createUserAgentEnricher(), createGeoEnricher()]
  nitroApp.hooks.hook('evlog:enrich', (ctx) => {
    for (const enricher of enrichers) enricher(ctx)
  })
})

// Next.js: in lib/evlog.ts
createEvlog({
  enrich: (ctx) => {
    for (const enricher of enrichers) enricher(ctx)
    ctx.event.region = process.env.VERCEL_REGION
  },
})

---

Auto-Redaction (PII Protection)

Built-in redaction scrubs sensitive data from wide events before console output and before any drain sees the data. Enabled by default in production (NODE_ENV === 'production'), disabled in development. Uses smart partial masking, preserving enough context for debugging.

// Disable in production (opt-out)
evlog: { redact: false }

// Add custom paths on top of built-ins
evlog: {
  redact: {
    paths: ['user.password', 'headers.authorization'],
  }
}

// Only specific built-ins
evlog: {
  redact: {
    builtins: ['email', 'creditCard'],
  }
}

// No built-ins, only custom (uses flat [REDACTED] replacement)
evlog: {
  redact: {
    builtins: false,
    paths: ['user.ssn'],
    patterns: [/SECRET_\w+/g],
  }
}

Built-in patterns with smart masking output:

Pattern	Example Input	Masked Output
creditCard	4111111111111111	****1111
email	[e-mail]	a***@***.com
ipv4	192.168.1.100	***.***.***.100
phone	[phone]	+33 ****5678
jwt	eyJhbGciOi...	eyJ***.***
bearer	Bearer sk_live_abc...	Bearer ***
iban	FR76 3000 6000 ...189	FR76****189

Works in all frameworks: Nuxt (evlog config), Nitro (evlog() module options), Next.js (createEvlog()), standalone (initLogger()), and all middleware integrations (Hono, Express, Fastify, Elysia, NestJS).

---

AI SDK Integration

Capture token usage, tool calls, model info, streaming metrics, tool execution timing, cost estimation, and embedding metadata from the Vercel AI SDK into wide events. Import from evlog/ai. Requires ai >=6.0.168 <8.0.0 as a peer dependency.

Basic setup (middleware)

import { createAILogger } from 'evlog/ai'

const log = useLogger(event) // or any RequestLogger
const ai = createAILogger(log)

const result = streamText({
  model: ai.wrap('anthropic/claude-sonnet-4.6'),  // accepts string or model object
  messages,
})

ai.wrap() uses model middleware to transparently capture all LLM calls. Works with generateText, streamText, and ToolLoopAgent.

Telemetry integration (deeper observability)

For tool execution timing, success/failure tracking, and total generation wall time, add createEvlogIntegration():

import { createAILogger, createEvlogIntegration } from 'evlog/ai'

const ai = createAILogger(log)

const agent = new ToolLoopAgent({
  model: ai.wrap('anthropic/claude-sonnet-4.6'),
  tools: { searchWeb, queryDatabase },
  stopWhen: stepCountIs(5),
  telemetry: {
    integrations: [createEvlogIntegration(ai)],
  },
})

This adds ai.tools (per-tool { name, durationMs, success, error? }) and ai.totalDurationMs to the wide event.

Embeddings

const { embedding, usage } = await embed({ model: embeddingModel, value: query })
ai.captureEmbed({ usage, model: 'text-embedding-3-small', dimensions: 1536 })

For embedMany, pass the batch count:

ai.captureEmbed({ usage, model: 'text-embedding-3-small', count: documents.length })

Cost estimation

Pass a pricing map to get ai.estimatedCost in the wide event:

const ai = createAILogger(log, {
  cost: {
    'claude-sonnet-4.6': { input: 3, output: 15 },
    'gpt-4o': { input: 2.5, output: 10 },
  },
})

Wide event ai field

Includes: calls, model, provider, inputTokens, outputTokens, totalTokens, cacheReadTokens, reasoningTokens, finishReason, toolCalls, steps, msToFirstChunk, msToFinish, tokensPerSecond, error, tools (via telemetry integration), totalDurationMs (via telemetry integration), embedding (via captureEmbed), estimatedCost (via cost option).

Anti-patterns to detect:

Anti-Pattern	Fix
Manual token tracking in onFinish	ai.wrap() — middleware captures automatically
console.log('tokens:', result.usage)	ai.wrap() — structured ai.* fields in wide event
No AI observability	Add createAILogger(log) + ai.wrap()
No tool execution timing	Add createEvlogIntegration(ai) to telemetry.integrations
Manual cost calculation	Use cost option in createAILogger()

---

Related Capabilities (pointers)

Recommend these when the review surfaces the matching need. Each has full docs on evlog.dev:

Need spotted	evlog answer	Docs
Auth'd user identity missing from events (Better Auth apps)	evlog/better-auth — identifyUser(), createAuthMiddleware(), client identity sync	https://www.evlog.dev/use-cases/better-auth/overview
Ad-hoc field names drifting across the codebase	Typed fields + error/audit catalogs (evlog/catalog)	https://www.evlog.dev/learn/typed-fields · https://www.evlog.dev/learn/catalogs
Cross-cutting hooks (request start/finish, client logs, logger extension)	Plugins — definePlugin	https://www.evlog.dev/extend/plugins
Tail logs live during dev / build a log viewer	createStreamDrain (evlog/stream, SSE) + readFsLogs / tailFsLogs (evlog/fs)	https://www.evlog.dev/extend/stream
Agents need to query logs over HTTP in dev	Memory adapter + readMemoryLogs() behind a dev-only endpoint	https://www.evlog.dev/integrate/adapters/self-hosted/memory

---

Structured Errors

import { createError } from 'evlog'  // required in Nuxt too: a bare createError is h3's

// Minimal
throw createError({ message: 'Database connection failed', status: 500 })

// Standard
throw createError({ message: 'Payment failed', status: 402, why: 'Card declined by issuer' })

// Complete
throw createError({
  message: 'Payment failed',
  status: 402,
  why: 'Card declined by issuer - insufficient funds',
  fix: 'Please use a different payment method or contact your bank',
  link: 'https://docs.example.com/payments/declined',
  cause: originalError,
})

// Backend-only context (wide events / drains — never HTTP body or parseError())
throw createError({
  message: 'Not allowed',
  status: 403,
  why: 'Insufficient permissions',
  internal: { correlationId: 'req_abc', resourceId: 'proj_123' },
})

Frontend: extract user-facing fields with parseError() (internal is never returned to clients):

import { parseError } from 'evlog'

const error = parseError(err)
// error.message, error.status, error.why, error.fix, error.link

See references/structured-errors.md for common patterns and templates.

---

Anti-Patterns to Detect

Anti-Pattern	Fix
Multiple console.log in one function	Single wide event with log.set()
throw new Error('...')	throw createError({ message, status, why, fix })
console.error(e); throw e	log.error(e); throw createError(...)
No logging in request handlers	Add useLogger(event) / useLogger() / createRequestLogger()
Flat log data { uid, n, t }	Grouped objects: { user: {...}, cart: {...} }
Logging sensitive data log.set({ user: body })	Explicit fields: { user: { id: body.id, plan: body.plan } } + enable redact: true
Putting support-only IDs in why / message	Use createError({ ..., internal: { ... } }) for non-user-facing diagnostics

See references/code-review.md for the full checklist.

---

Loading Reference Files

Load based on what you're working on, and do not load all at once:

• Designing wide events → references/wide-events.md
• Improving errors → references/structured-errors.md
• Full code review → references/code-review.md
• Drain pipeline setup → references/drain-pipeline.md