# Langfuse > Use Langfuse for LLM observability and evaluation and look up Langfuse documentation. In HybridClaw, data access (traces, observations, sessions, scores, prompts, datasets, metrics) goes through the gateway-proxied langfuse.cjs helper with SecretRef auth — reads are green, writes are grant-gated. Documentation retrieval uses langfuse.com llms.txt, markdown pages, and search-docs. Covers instrumentation, prompt migration, error analysis, and LLM-as-a-judge calibration. - Skill: `hybridaione/langfuse` (Agent Skill, multi-file: 14 files) - Install (CLI): `npx skillmds@latest add hybridaione/langfuse` - Raw SKILL.md: https://api.skillmd.com/api/skills/hybridaione/langfuse/raw - Safety review: pending - Works with: Claude Code, Claude.ai, OpenAI Codex - Category: AI & ML - Author: HybridAIOne (https://skillmd.com/u/hybridaione) - Updated: 2026-09-21 - Page: https://skillmd.com/skills/hybridaione/langfuse --- # Langfuse This skill helps you use Langfuse effectively across all common workflows: instrumenting applications, migrating prompts, debugging traces, accessing data, and evaluating outputs. > **HybridClaw integration.** This is the official Langfuse skill > ([github.com/langfuse/skills](https://github.com/langfuse/skills), MIT) > adapted for HybridClaw. Two things differ from the upstream skill: > > 1. **Credentials never leave the gateway.** Do not export > `LANGFUSE_PUBLIC_KEY` / `LANGFUSE_SECRET_KEY`, run `npx langfuse-cli`, or > paste keys anywhere. Store them once in the runtime stores (below); the > gateway injects them server-side. > 2. **Data access goes through `langfuse.cjs`**, not the Langfuse CLI. The > helper builds each REST request and sends it through the HybridClaw gateway, > which resolves `Authorization: Basic ` and the > `` base URL. Wherever a reference says to run > `langfuse-cli` or `curl -H "Authorization: Basic $AUTH"`, use the helper > instead. Documentation retrieval (section 2) is unchanged. ## HybridClaw setup The helper never sees credentials. Store two values once. For secrets, use this order: 1. Browser admin: open the active HybridClaw admin URL ending in `/admin/secrets`. 2. Browser `/chat` or TUI fallback. 3. Local console fallback. 1. `LANGFUSE_BASIC_AUTH` — base64 of `public-key:secret-key`: `/secret set LANGFUSE_BASIC_AUTH ""` 2. `LANGFUSE_HOST` — your Langfuse base URL: `/env set LANGFUSE_HOST https://cloud.langfuse.com` (use `https://us.cloud.langfuse.com` for US, `https://jp.cloud.langfuse.com` for JP, or your self-hosted origin). Local console fallback: `hybridclaw secret set LANGFUSE_BASIC_AUTH "<...>"` and `hybridclaw env set LANGFUSE_HOST https://cloud.langfuse.com`. See [references/operator-setup.md](references/operator-setup.md) for key scope, host selection, autonomy defaults, and network-policy notes. ## Core Principles Follow these principles for ALL Langfuse work: 1. **Documentation first**: never implement from memory. Langfuse updates frequently — fetch current docs (section 2) before writing instrumentation or SDK code. 2. **Helper for data access**: use `langfuse.cjs` (gateway + SecretRef) when querying or modifying Langfuse data. It owns endpoints, methods, bodies, stakes tiers, host, and the Basic auth placeholder. 3. **Best practices by use case**: check the relevant reference below before implementing. 4. **Use latest Langfuse versions**: unless the user says otherwise, target the latest Langfuse SDKs/APIs. ## Use-case references - instrumenting an existing function/application: [references/instrumentation.md](references/instrumentation.md) - migrating prompts from a codebase into Langfuse: [references/prompt-migration.md](references/prompt-migration.md) - capturing user feedback (thumbs, ratings, implicit signals) as scores: [references/user-feedback.md](references/user-feedback.md) - systematic error analysis — reading traces, building a failure taxonomy, deciding what to fix: [references/error-analysis.md](references/error-analysis.md) - judge calibration (LLM-as-a-Judge reliability, accuracy checks, confusion matrices, metric ingestion): [references/judge-calibration.md](references/judge-calibration.md) - upgrading or migrating Langfuse SDKs: [references/sdk-upgrade.md](references/sdk-upgrade.md) - CI/CD experiment gates with `langfuse/experiment-action`: [references/ci-cd.md](references/ci-cd.md) - raw Langfuse REST/CLI semantics (endpoints, pagination, v2 vs legacy): [references/cli.md](references/cli.md) - HybridClaw credential, host, autonomy, and network-policy setup: [references/operator-setup.md](references/operator-setup.md) - submitting feedback about this skill: [references/skill-feedback.md](references/skill-feedback.md) ## 1. Langfuse data access (HybridClaw gateway helper) `langfuse.cjs` is the API wrapper. Do not handcraft Langfuse API URLs, JSON bodies, tiers, host, or the Basic auth header from memory. ```bash node skills/langfuse/langfuse.cjs --help ``` - **plan** classifies a natural-language request into an operation + tier: `node skills/langfuse/langfuse.cjs --format json plan "average eval score this week"` - **run** executes a live request through the gateway (the gateway injects the Basic auth header): `node skills/langfuse/langfuse.cjs --format json run list-traces --user-id alice --limit 50` - **http-request** emits the gateway-ready payload without calling Langfuse — use it for dry-run inspection or runtimes without helper gateway access. Read examples (green): ```bash node skills/langfuse/langfuse.cjs --format json run get-trace --trace-id abc123 node skills/langfuse/langfuse.cjs --format json run list-observations --type GENERATION --trace-id abc123 node skills/langfuse/langfuse.cjs --format json run list-scores --name quality node skills/langfuse/langfuse.cjs --format json run get-prompt --prompt-name support-reply --label production node skills/langfuse/langfuse.cjs --format json run metrics --query '{"view":"traces","metrics":[{"measure":"count","aggregation":"count"}]}' ``` Guarded write examples (amber — only after an explicit operator grant): ```bash node skills/langfuse/langfuse.cjs --format json run create-score \ --trace-id abc123 --name quality --value 0.8 --data-type NUMERIC --comment "reviewed" --operator-grant node skills/langfuse/langfuse.cjs --format json run create-prompt \ --name summarizer --type text --prompt "Summarize: {{input}}" --label production --operator-grant ``` Select region or self-hosted host explicitly (otherwise ``): ```bash node skills/langfuse/langfuse.cjs --format json run list-traces --host https://us.cloud.langfuse.com ``` ### Working rules - Reads are green. Writes (`create-score`, `create-comment`, `create-dataset`, `create-dataset-item`, `create-prompt`) require `--operator-grant`: produce a plan, wait for the operator's grant, then run the exact approved command. - Deletions and project / API-key / organization / SCIM administration are out of scope. Use the Langfuse UI for those. - Page size is capped at 100; use `--page` (legacy) or `--cursor` (modern endpoints) to paginate. The helper rejects `--limit` above 100. - Trace reads use Langfuse's v2 Observations API. `list-traces` returns logical root observation rows (one application root per trace); `get-trace` returns every observation row sharing the requested trace ID. Follow `meta.cursor` with `--cursor` when more rows are available. - Langfuse v4 has no separate trace-level `input`/`output`. Reconstruct them from the root observation; prompts and outputs may instead live on a child `GENERATION` observation. - Before creating a score config, list existing ones (`list-score-configs`); configs cannot be deleted. - Never print, inspect, or ask for `LANGFUSE_BASIC_AUTH`; the gateway injects it as `Authorization: Basic `. - Cost per assistant run is recorded by HybridClaw `UsageTotals`; helper output includes `costMeasurement.system = "UsageTotals"` for eval verification. ## 2. Langfuse documentation Prefer your application's native web fetch/search tools (e.g. `web_fetch`, `web_search`) over `curl`. The URLs work with any fetching method. ### 2a. Documentation index (llms.txt) Fetch the full index of doc pages, then fetch the right one: ```bash curl -s https://langfuse.com/llms.txt ``` ### 2b. Fetch individual pages as markdown Append `.md` to any doc path (or send `Accept: text/markdown`): ```bash curl -s "https://langfuse.com/docs/observability/overview.md" ``` ### 2c. Search documentation When you don't know the page (also indexes GitHub issues/discussions): ```bash curl -s "https://langfuse.com/api/search-docs?query=How+do+I+trace+LangGraph+agents" ``` Workflow: start with **llms.txt** to orient → **fetch the specific page** → fall back to **search** when the topic is unclear. ## Eval suite ```bash node skills/langfuse/langfuse.cjs --format json eval-scenarios ``` The fixture at `evals/scenarios.json` contains 10 scenarios covering trace, observation, session, score, metric, prompt, and dataset reads plus guarded score, dataset, and prompt writes. ## Skill feedback If the skill gives wrong or outdated guidance, is missing something, or could be improved, offer to submit feedback to the Langfuse skill maintainers following [references/skill-feedback.md](references/skill-feedback.md). Do **not** trigger this for issues with Langfuse the product — only this skill's instructions. ## Attribution Adapted from the official Langfuse skill ([github.com/langfuse/skills](https://github.com/langfuse/skills)), MIT-licensed, with HybridClaw gateway/SecretRef data access in place of the upstream `langfuse-cli` + plaintext-key path. See [NOTICE.md](NOTICE.md). ## Validation ```bash python3 skills/skill-creator/scripts/quick_validate.py skills/langfuse node skills/langfuse/langfuse.cjs --help node skills/langfuse/langfuse.cjs --format json eval-scenarios ```