langfuse

name	langfuse
description	Use Langfuse. Trigger when querying or modifying Langfuse data, reading Langfuse docs, instrumenting traces, migrating prompts, managing datasets/scores/sessions, or debugging Langfuse usage.
allowed-tools	["WebFetch(domain:langfuse.com)","Bash(curl *langfuse.com/*)","Bash(npx langfuse-cli api __schema *)","Bash(npx langfuse-cli api * --help *)","Bash(npx langfuse-cli api * list *)","Bash(npx langfuse-cli api * get *)","Bash(bunx langfuse-cli api __schema *)","Bash(bunx langfuse-cli api * --help *)","Bash(bunx langfuse-cli api * list *)","Bash(bunx langfuse-cli api * get *)"]

Langfuse

Use this for Langfuse data access, docs lookup, instrumentation, prompt migration, trace debugging, feedback scores, evaluation, and CI gates.

Core Principles

Follow these for all Langfuse work:

1. Docs first: fetch current docs before implementation.
2. CLI for data: use langfuse-cli for Langfuse API data access.
3. Branch by use case: read the relevant reference before implementing.
4. Current SDKs: prefer latest Langfuse SDK/API guidance unless constrained.

Use case specific references

• instrumenting an existing function/application: references/instrumentation.md
• migrating prompts from a codebase into Langfuse: references/prompt-migration.md
• capturing user feedback (thumbs, ratings, implicit signals) as scores on traces: references/user-feedback.md
• further tips on using the Langfuse CLI: references/cli.md
• upgrading or migrating Langfuse SDKs to the latest version: references/sdk-upgrade.md
• judge calibration (LLM-as-a-Judge reliability, simple accuracy checks, advanced split-based validation, confusion matrices, and metric ingestion): references/judge-calibration.md
• systematic error analysis — reading traces, building failure taxonomy, deciding what to fix: references/error-analysis.md
• setting up CI/CD experiment gates with langfuse/experiment-action: references/ci-cd.md
• submitting feedback about this skill: references/skill-feedback.md

1. Langfuse API via CLI

Use langfuse-cli for Langfuse REST API access. Run via npx:

Start by discovering the schema and available arguments:

# Discover all available resources
npx langfuse-cli api __schema

# List actions for a resource
npx langfuse-cli api <resource> --help

# Show args/options for a specific action
npx langfuse-cli api <resource> <action> --help

Credentials

Set environment variables before calls:

export LANGFUSE_PUBLIC_KEY=pk-lf-...
export LANGFUSE_SECRET_KEY=sk-lf-...
export LANGFUSE_BASE_URL=https://cloud.langfuse.com # example for EU cloud. For US cloud it's us.cloud.langfuse.com, and can also be a self-hosted URL. The server must always be specified in order to access Langfuse.

If LANGFUSE_BASE_URL is used instead of LANGFUSE_HOST, run export LANGFUSE_HOST="$LANGFUSE_BASE_URL". If credentials are missing, ask the user to set them in a shell or .env file. Do not ask them to paste keys into chat.

Detailed CLI Reference

For common workflows, see references/cli.md.

2. Langfuse Documentation

Three methods to access Langfuse docs. Prefer native web fetch/search tools over curl when available; the curl examples are illustrative.

2a. Documentation Index (llms.txt)

Fetch the full documentation index:

curl -s https://langfuse.com/llms.txt

Use this to find the right page, then fetch that page directly.

2b. Fetch Individual Pages as Markdown

Any listed page can be fetched as markdown by appending .md or using Accept: text/markdown.

curl -s "https://langfuse.com/docs/observability/overview.md"
curl -s "https://langfuse.com/docs/observability/overview" -H "Accept: text/markdown"

2c. Search Documentation

Search when the relevant page is unclear:

curl -s "https://langfuse.com/api/search-docs?query=<url-encoded-query>"

Example:

curl -s "https://langfuse.com/api/search-docs?query=How+do+I+trace+LangGraph+agents"

Returns a JSON response with:

• query: the original query
• answer: a JSON string containing an array of matching documents, each with:
  • url: link to the doc page
  • title: page title
  • source.content: array of relevant text excerpts from the page

Search responses can be large; extract only the relevant portions.

Documentation Workflow

1. Start with llms.txt to orient.
2. Fetch specific pages when you identify the right one.
3. Search when the topic is unclear.

Skill Feedback

When the user says this skill is wrong, stale, missing coverage, or behaving badly, offer to submit feedback to the Langfuse skill maintainers. This includes:

• The skill gave wrong or outdated instructions
• A workflow didn't produce the expected result
• The user wishes the skill covered something it doesn't
• The user explicitly says something like "this should work differently" or "this is wrong"

Do NOT trigger this for issues with Langfuse itself (the product) — only for issues with this skill's instructions and behavior.

When triggered, follow the process in references/skill-feedback.md.