tracelift

I kept exporting agent traces and then writing the same throwaway pandas script to answer three questions: which tool calls failed, what each step cost, and where the latency went. tracelift is that script, done properly once: a Rust core that parses the trace file and a small polars-based API on top.

It is a file analyzer, not an observability platform. No collector, no storage, no dashboard to run. If you can export your traces to JSONL or OTLP-JSON, you can point tracelift at the file and get answers.

Install

pip install tracelift

Use it from the command line

tracelift summarize traces.jsonl

Running it on the demo file in this repo:

tests/fixtures/sample.jsonl: 5 spans across 2 traces, 2 skipped
window  2025-06-09 20:13:20 -> 2025-06-09 20:13:34 UTC
calls   3 llm / 1 tool
errors  1 (20.0%)
cost    $0.0248
tokens  2,500 in / 680 out
latency llm p50 1800ms p95 3000ms  tool p50 400ms p95 400ms

cost by model
  model                        spans   cost       input_tokens  output_tokens
  gpt-4o-2024-08-06            1       $0.0145    1,200         350
  claude-sonnet-4-6           1       $0.0092    900           210
  claude-haiku-4-5-20251001   1       $0.0011    400           120

failing tools
  tool_name     failures  example
  search_web    1         TimeoutError

Add --json to get the same summary as JSON for scripts and CI.

Use it from Python

import tracelift

traces = tracelift.load("traces.jsonl")

traces.failures()                    # every span with status == "error"
traces.cost_by("model")              # or tool_name, agent_name, provider, kind
traces.slowest(10)
traces.token_totals()
traces.latency_breakdown("trace-id")  # spans in tree order, with self time
traces.df                            # the underlying polars DataFrame

Every helper hands back a polars DataFrame, so the moment you need something tracelift does not do directly, it is one group_by away. The library does not hide the data from you.

Speed

The reason this is in Rust and not the pandas script: parsing a 889 MB / 3,000,000-span JSONL file, against an idiomatic pandas loader that builds the exact same columns. 16-core i7-13620H, polars 1.41, median of three runs.

About 6x faster to load and 2.6x less memory; roughly 5.6x faster once the aggregations are included. The numbers are hardware-specific. To check them yourself: python bench/generate.py bench/data/big.jsonl --spans 3000000 then python bench/run.py bench/data/big.jsonl. Method and caveats are in bench/RESULTS.md.

What it reads

JSONL, one span per line. Either flat fields that match the schema below, or an attributes object using OpenTelemetry GenAI semantic convention keys (gen_ai.provider.name, gen_ai.usage.input_tokens, gen_ai.tool.name, and so on). The older alias names still emitted by a lot of tooling (gen_ai.system, gen_ai.usage.prompt_tokens, gen_ai.usage.completion_tokens) are accepted too.

OTLP-JSON, the resourceSpans shape that OpenTelemetry SDK file exporters and the collector's file exporter produce, as a single document or one export per line.

A broken line never takes down the parse. Bad lines are skipped, counted, and a few samples are kept in traces.report so you can see what was dropped.

The span table

One row per span:

trace_id, span_id, parent_span_id, name, kind (llm / tool / agent / chain / other), start_ns, end_ns, duration_ms, provider, model, input_tokens, output_tokens, cache_read_tokens, cost, tool_name, tool_call_id, agent_name, conversation_id, error_type, status (ok / error / unset).

One deliberate choice: cost is read from the trace if it is there, and left null if it is not. tracelift will not multiply tokens by a built-in price list, because those lists go stale and a wrong number that looks right is worse than an honest blank.

What it does not do

• OTLP protobuf input. JSON only for now.
• Collecting traces. It reads files you already have.
• Estimating cost from token counts. See above.
• Scrubbing names or PII. Strip anything sensitive before you share a report.

Building from source

Rust core in core/, the PyO3 bindings in bindings/, the Python API and CLI in python/tracelift/. cargo test covers the parser, pytest covers the API and CLI. For a local dev build you need a Rust toolchain, then pip install -e . --no-build-isolation.

License

MIT