Tracing

Overview

loop-telemetry exports traces over OTLP/HTTP. Spans cover the agent run, a model generation, and individual tool calls. The crate is not linked into the default binary.

cargo build -p loop-cli --release --features telemetry

With that build, the TUI has /tracing and headless --print runs accept --trace-* flags.

Destinations

Backend	`/tracing setup`	Typical target
Langfuse	`langfuse`	Langfuse cloud or a self-hosted host
OTLP	`otlp` (alias `otel`)	Jaeger, Phoenix, Tempo, or an OpenTelemetry collector

Tracing turns on when a destination resolves, unless you ran /tracing disable. Langfuse can also be configured entirely from the environment. When all three are set, they take precedence over values saved by the wizard:

Variable	Purpose
`LANGFUSE_HOST`	Base URL (default suggestion: `https://cloud.langfuse.com`)
`LANGFUSE_PUBLIC_KEY`	Public key
`LANGFUSE_SECRET_KEY`	Secret key

The secret is stored in the credential store (langfuse), not in settings.json. An OTLP Authorization header value is stored under otlp. Saved URLs and the Langfuse public key live in the global tracing settings block. Project settings cannot redirect traces.

In the TUI

/tracing                  # status
/tracing enable
/tracing disable
/tracing setup            # pick Langfuse or OTLP
/tracing setup langfuse
/tracing setup otlp

/tracing setup walks through host and keys. Escape cancels the wizard.

Headless traces

Each loop --print run is one trace rooted at loop.print. The trace id is printed on stderr:

loop-trace-id: <hex>

loop --print "explain this crate" \
  --trace-name bench-repair \
  --trace-tag swe-bench \
  --trace-metadata task=django__django-1234 \
  --trace-session run-7 \
  --trace-env benchmark

Flag	Description
`--trace-name`	Trace name (default `loop.print`)
`--trace-tag`	Tag; repeatable
`--trace-metadata key=value`	Metadata; repeatable
`--trace-session`	Langfuse session id (default: the Loop session id)
`--trace-env`	Environment label, for example `benchmark`
`--trace-parent`	W3C `traceparent` of an enclosing span (also `TRACEPARENT`)

These flags exist only in a telemetry build. A default binary rejects them.

Settings

{
  "tracing": {
    "enabled": true,
    "backend": "langfuse",
    "langfuseHost": "https://cloud.langfuse.com",
    "langfusePublicKey": "pk-lf-…"
  }
}

backend is langfuse or otlp. For OTLP, set otlpEndpoint (default suggestion http://localhost:4318).

Getting Started

Guides

Features

Overview

Destinations

In the TUI

Headless traces

Settings

​Overview

​Destinations

​In the TUI

​Headless traces

​Settings

Overview

Destinations

In the TUI

Headless traces

Settings