Tail Logger

A Tail Worker that receives TraceItem batches from producer Workers, keeps the last 50 events in Workers KV, and exposes them over HTTP for inspection.

FeaturesCopy Anchor Link

• tail handler - receives TraceItem batches and stores key recent
• GET /logs - read recent events
• DELETE /logs - clear stored events

API ReferenceCopy Anchor Link

GET /logsCopy Anchor Link

Example RequestCopy Anchor Link

curl "https://your-worker.workers.dev/logs"

Success ResponseCopy Anchor Link

{
  "events": [
    {
      "scriptName": "my-producer",
      "outcome": "ok",
      "eventTimestamp": 1710000000000,
      "logs": ["request handled"]
    }
  ],
  "count": 1
}

DELETE /logsCopy Anchor Link

Example RequestCopy Anchor Link

curl -X DELETE "https://your-worker.workers.dev/logs"

Success ResponseCopy Anchor Link

{
  "cleared": true
}

Configuring a producerCopy Anchor Link

In the producer Worker's wrangler.json, add this Worker as a tail consumer:

{
  "name": "my-producer",
  "tail_consumers": [{ "service": "tail-logger" }]
}

Deploy tail-logger first, then the producer. When the producer handles requests, its traces are delivered to this Worker's tail handler.

Use CasesCopy Anchor Link

• Learn Tail Workers / tail_consumers wiring
• Debug producer Workers without streaming wrangler tail locally
• Keep a short rolling window of outcomes and console logs
• Teach observability patterns across Workers

LimitationsCopy Anchor Link

• Stores only the last 50 events in a single KV key
• Tail delivery from another Worker typically requires deployed Workers
• No filtering UI - raw recent events only
• No authentication on /logs

DeploymentCopy Anchor Link

curl "https://your-worker.workers.dev/logs"

Local DevelopmentCopy Anchor Link

cd apps/experiments/tail-logger
npm install
npm run dev

curl "http://localhost:8787/logs"

Tail delivery from another Worker typically requires deployed Workers; unit tests call the tail export directly with mock events.

ConfigurationCopy Anchor Link

wrangler.json declares:

• KV namespace TAIL_LOGS

Cloudflare Features UsedCopy Anchor Link

• Workers - Edge compute runtime
• Tail Workers - Consume traces from other Workers
• Workers KV - Rolling store for recent events