Langfuse

This skill helps you use Langfuse effectively across all common workflows: instrumenting applications, migrating prompts, debugging traces, and accessing data programmatically.

Core Principles

Follow these principles for ALL Langfuse work:

Documentation First

NEVER implement based on memory. Always fetch current docs before writing code (Langfuse updates frequently) See the section below on how to access documentation.

CLI for Data Access

Use

langfuse-cli

when querying/modifying Langfuse data. See the section below on how to use the CLI.

Best Practices by Use Case

Check the relevant reference file below for use-case-specific guidelines before implementing

Use latest Langfuse versions

Unless the user specified otherwise or there's a good reason, always use the latest version of Langfuse SDKs/APIs. 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 submitting feedback about this skill: references/skill-feedback.md 1. Langfuse API via CLI Use the langfuse-cli to interact with the full Langfuse REST API from the command line. Run via npx (no install required): 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 making calls: export LANGFUSE_PUBLIC_KEY = pk-lf- .. . export LANGFUSE_SECRET_KEY = sk-lf- .. . export LANGFUSE_HOST = 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 not set, ask the user for their API keys (found in Langfuse UI → Settings → API Keys).

Detailed CLI Reference

For common workflows, tips, and full usage patterns, see

references/cli.md

.

2. Langfuse Documentation

Three methods to access Langfuse docs, in order of preference.

Always prefer your application's native web fetch and search tools

(e.g.,

WebFetch

,

WebSearch

,

mcp_fetch

, etc.) over

curl

when available. The URLs and patterns below work with any fetching method — the

curl

examples are just illustrative.

2a. Documentation Index (llms.txt)

Fetch the full index of all documentation pages:

curl

-s

https://langfuse.com/llms.txt

Returns a structured list of every doc page with titles and URLs. Use this to discover the right page for a topic, then fetch that page directly.

Alternatively, you can start on

https://langfuse.com/docs

and explore the site to find the page you need.

2b. Fetch Individual Pages as Markdown

Any page listed in llms.txt can be fetched as markdown by appending

.md

to its path or by using

Accept: text/markdown

in the request headers. Use this when you know which page contains the information needed. Returns clean markdown with code examples and configuration details.

curl

-s

"https://langfuse.com/docs/observability/overview.md"

curl

-s

"https://langfuse.com/docs/observability/overview"

-H

"Accept: text/markdown"

2c. Search Documentation

When you need to find information across all docs and github issues/discussions without knowing the specific page:

curl

-s

"https://langfuse.com/api/search-docs?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 is a great fallback if you cannot find the relevant pages or need more context. Especially useful when debugging issues as all GitHub Issues and Discussions are also indexed. Responses can be large — extract only the relevant portions. Documentation Workflow Start with llms.txt to orient — scan for relevant page titles Fetch specific pages when you identify the right one Fall back to search when the topic is unclear and you want more context Skill Feedback When the user expresses that something about this skill is not working as expected, gives incorrect guidance, is missing information, or could be improved — offer to submit feedback to the Langfuse skill maintainers. This includes when: 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 .