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When an LLM workflow fails or produces bad output, you need to understand what happened — what data each step received, what the LLM returned, and where things went wrong. Tracing gives you that visibility. Every workflow run produces a trace: a tree of events showing the workflow and every step, evaluator, child workflow, LLM call, and HTTP call with their inputs, outputs, errors, and timing. Traces are written automatically when the worker runs. You don’t need to add any instrumentation to your code — just turn tracing on and tell it where to write.

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What Gets Traced

Each workflow execution produces a trace tree. The root is the workflow, and children are everything that ran inside it:
  • Steps and evaluators — input, output (or error), start/end timestamps
  • LLM calls — the prompt name, variables, loaded config, the result, and token usage (inputTokens, outputTokens, totalTokens)
  • HTTP calls — method, URL, status code
  • Child workflows — nested as their own trees with the same structure
This means you can open a trace file and see the full picture: which steps ran, what the LLM received and returned, how many tokens it used, and exactly where a failure happened.

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Enabling Tracing

Tracing is off by default. You enable it with environment variables. Local tracing writes JSON files to disk — no extra services needed. Remote tracing uploads to S3 when a run completes (requires Redis to correlate events). You can disable trace generation for specific workflows with options.disableTrace: true — see Workflow options. Local only (recommended to start): 
OUTPUT_TRACE_LOCAL_ON=true
Trace files appear at logs/runs/<workflowName>/<timestamp>_<workflowId>.json under your project root. Local + remote: 
OUTPUT_TRACE_LOCAL_ON=true
OUTPUT_TRACE_REMOTE_ON=true
OUTPUT_REDIS_URL=redis://localhost:6379
OUTPUT_TRACE_REMOTE_S3_BUCKET=my-traces
OUTPUT_AWS_REGION=us-east-1
OUTPUT_AWS_ACCESS_KEY_ID=...
OUTPUT_AWS_SECRET_ACCESS_KEY=...

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All Environment Variables

VariableRequired whenDescription
OUTPUT_TRACE_LOCAL_ONLocal tracingSet to true to write trace files to disk
OUTPUT_TRACE_REMOTE_ONRemote tracingSet to true to upload traces to S3 on run completion
OUTPUT_REDIS_URLRemote tracingRedis address for correlating events before S3 upload
OUTPUT_REDIS_TRACE_TTLRemote tracingTTL in seconds for Redis keys that accumulate trace events before a workflow is uploaded. Default: 7 days (604800).
OUTPUT_TRACE_REMOTE_S3_BUCKETRemote tracingS3 bucket name
OUTPUT_AWS_REGIONRemote tracingAWS region for the bucket
OUTPUT_AWS_ACCESS_KEY_IDRemote tracingAWS access key
OUTPUT_AWS_SECRET_ACCESS_KEYRemote tracingAWS secret key
OUTPUT_TRACE_HOST_PATHDocker setupsHost path where trace files are mounted. The worker writes inside the container; this tells the API and CLI what path to report so you can open files on the host

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Reading a Trace

Each trace file is a single JSON object — the root workflow node. Every node in the tree has the same shape:
FieldDescription
idUnique identifier for this node
kindworkflow, step, evaluator, llm, or http
nameWorkflow name or activity type
startedAt / endedAtUnix timestamps (ms)
inputWhat the node received
outputWhat the node returned (absent on error)
errorError details with name, message, stack (absent on success)
childrenArray of child nodes (same shape)

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Step with an LLM Call

This is the most common trace shape you’ll see. The step has the LLM call as a child, so you can see exactly what prompt was loaded, what variables were passed, what the LLM returned, and how many tokens it used: 
{
  "id": "1",
  "kind": "step",
  "name": "lead_enrichment#generateSummary",
  "startedAt": 1761952643861,
  "endedAt": 1761952649808,
  "input": { "name": "Acme Corp", "industry": "SaaS", "size": 250 },
  "output": "Acme Corp is a B2B SaaS company...",
  "children": [
    {
      "id": "generateText-1761952643867",
      "kind": "llm",
      "name": "generateText",
      "startedAt": 1761952643867,
      "endedAt": 1761952649806,
      "input": {
        "prompt": "generate_summary@v1",
        "variables": { "companyName": "Acme Corp", "industry": "SaaS" },
        "loadedPrompt": {
          "name": "generate_summary@v1",
          "config": { "provider": "anthropic", "model": "claude-sonnet-4-20250514" }
        }
      },
      "output": {
        "result": "Acme Corp is a B2B SaaS company...",
        "usage": { "inputTokens": 38, "outputTokens": 204, "totalTokens": 242 }
      },
      "children": []
    }
  ]
}

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Failed Step

When a step fails, it has an error object instead of output. The error includes the name, message, and stack trace: 
{
  "id": "1",
  "kind": "step",
  "name": "lead_enrichment#lookupCompany",
  "startedAt": 1766083745644,
  "endedAt": 1766083745645,
  "error": {
    "name": "FatalError",
    "message": "HubSpot API key is invalid",
    "stack": "FatalError: HubSpot API key is invalid\n    at fn (...steps.js:7:15)\n..."
  },
  "children": []
}
The parent workflow node also gets an error when the run fails, so you can see at the root level that something went wrong.

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Full Workflow Trace

A complete trace puts it all together — the workflow root with all its step children: 
{
  "id": "lead_enrichment-758d51b8-7bc0-40a4-b851-c692dff14910",
  "kind": "workflow",
  "name": "lead_enrichment",
  "startedAt": 1769527009211,
  "endedAt": 1769527009265,
  "input": { "companyDomain": "acme.com" },
  "output": {
    "output": { "company": "Acme Corp", "summary": "Acme Corp is a B2B SaaS company..." },
    "trace": {
      "destinations": {
        "local": "/path/to/logs/runs/lead_enrichment/2026-01-27_lead_enrichment-758d51b8-....json",
        "remote": null
      }
    }
  },
  "children": [
    {
      "id": "1",
      "kind": "step",
      "name": "lead_enrichment#lookupCompany",
      "startedAt": 1769527009222,
      "endedAt": 1769527009223,
      "input": "acme.com",
      "output": { "name": "Acme Corp", "industry": "SaaS", "size": 250 },
      "children": []
    },
    {
      "id": "2",
      "kind": "step",
      "name": "lead_enrichment#generateSummary",
      "input": { "name": "Acme Corp", "industry": "SaaS", "size": 250 },
      "output": "Acme Corp is a B2B SaaS company...",
      "children": [{ "kind": "llm", "..." : "..." }]
    },
    {
      "id": "3",
      "kind": "evaluator",
      "name": "lead_enrichment#judgeSummaryQuality",
      "input": { "summary": "Acme Corp is a B2B SaaS company...", "companyName": "Acme Corp" },
      "output": { "value": true, "confidence": 0.92, "reasoning": "Meets all criteria" },
      "children": [{ "kind": "llm", "..." : "..." }]
    }
  ]
}

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Child Workflows

Child workflows appear as kind: "workflow" children with their own nested tree of steps: 
{
  "id": "parent-44710c05-child-081d68e7",
  "kind": "workflow",
  "name": "child_workflow",
  "startedAt": 1766179342625,
  "endedAt": 1766179342636,
  "input": { "companyDomain": "acme.com" },
  "output": { "result": "..." },
  "children": [
    { "kind": "step", "name": "child_workflow#someStep", "..." : "..." }
  ]
}

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Continue-as-New

When a workflow calls continueAsNew, the trace records "<continued_as_new>" as the output for that run. The new run keeps the same workflow ID but gets a new start time — each run produces its own trace file. To see the full chain, list trace files for that workflow name and match by workflow ID; sort by timestamp for order.

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Accessing Traces

You can access traces in three ways: