Getting it into your agent
One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.
npx skills add vibeeval/vibecosystem --skill braintrust-tracinggit clone --depth 1 https://github.com/vibeeval/vibecosystemWrote this? Show the measurements
A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.
[](https://agentmods.dev/skills/vibeeval/vibecosystem/braintrust-tracing)<a href="https://agentmods.dev/skills/vibeeval/vibecosystem/braintrust-tracing"><img src="https://agentmods.dev/badge/skills/vibeeval/vibecosystem/braintrust-tracing/github.svg" alt="Measured on agentmods" height="20"></a>Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.
<a href="https://agentmods.dev/skills/vibeeval/vibecosystem/braintrust-tracing"><img src="https://agentmods.dev/badge/skills/vibeeval/vibecosystem/braintrust-tracing.svg" alt="Reviewed on agentmods" width="80" height="20"></a>What it costs to keep this loaded
Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.
| Model | Per session | Once invoked |
|---|---|---|
| Fable 5.1 | $0.00020 | $0.03160 |
| Opus 5 | $0.00010 | $0.01580 |
| Sonnet 5 | $0.00004 | $0.00632 |
| Haiku 4.5 | $0.00002 | $0.00316 |
Grade B, and why
braintrust-tracing scanned grade B with 1 finding against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 5d ago.
A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.
Reads agent configuration directoriesmediumAgent snooping
.claude/, .codex/, .gemini/ hold keys, settings and other credentials a mod has no legitimate need for.
tail -f ~/.claude/state/braintrust_hook.log This is a copy
100% identical to braintrust-tracing — 734 lines differ, which has more behind it and is treated as the original. This page carries a canonical link to it rather than competing with it.
How it starts
The opening of the file, as written. The whole thing — 368 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Braintrust Tracing for Claude Code
Comprehensive guide to tracing Claude Code sessions in Braintrust, including sub-agent correlation.
Architecture Overview
PARENT SESSION
+---------------------+
| SessionStart |
| (creates root) |
+----------+----------+
|
+----------v----------+
| UserPromptSubmit |
| (creates Turn) |
+----------+----------+
|
+--------------------+--------------------+
| | |
+---------v--------+ +--------v--------+ +--------v--------+
| PostToolUse | | PostToolUse | | PreToolUse |
| (Read span) | | (Edit span) | | (Task - inject) |
+------------------+ +-----------------+ +--------+--------+
|
+----------v----------+
| SUB-AGENT |
| SessionStart |
| (NEW root_span_id)|
+----------+----------+
|
+----------v----------+
| SubagentStop |
| (has session_id) |
+---------------------+
Hook Event Flow
| Hook | Trigger | Creates | Key Fields |
|---|---|---|---|
| SessionStart | Session begins | Root span | session_id, root_span_id |
| UserPromptSubmit | User sends prompt | Turn span | prompt, turn_number |
| PreToolUse | Before tool runs | (modifies Task prompts) | tool_input.prompt |
| PostToolUse | After tool runs | Tool span | tool_name, input, output |
| Stop | Turn completes | LLM spans | model, tokens, tool_calls |
| SubagentStop | Sub-agent finishes | (no span) | session_id of sub-agent |
| SessionEnd | Session ends | (finalizes root) | turn_count, tool_count |
What this file has done since we first saw it
Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.
- 5d ago First seen · 368 lines · 20 tokens per session scan B d5a8155d9977
braintrust-tracing is a skill published in the GitHub repository vibeeval/vibecosystem (529 stars, last pushed 1mo ago), licensed MIT. It adds 20 tokens to every session and 3,160 once invoked, about $0.0001 per session on Opus 5. A static security scan graded it B with 1 finding (reads agent configuration directories). It is 100% identical to braintrust-tracing, differing in 734 lines, and is treated as a copy.
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