How to integrate Langfuse MCP with Codex

Codex is one of the most popular coding harnesses out there. And MCP makes the experience even better. With Langfuse MCP integration, you can draft, triage, summarise emails, and much more, all without leaving the terminal or the app, whichever you prefer.

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Api Key

Langfuse is an open source LLM engineering platform for traces, evals, prompt management, and metrics. It helps teams debug, monitor, and improve LLM applications with clear observability data.

10 Tools

Introduction

Codex is one of the most popular coding harnesses out there. And MCP makes the experience even better. With Langfuse MCP integration, you can draft, triage, summarise emails, and much more, all without leaving the terminal or the app, whichever you prefer.

Also integrate Langfuse with

Why use Composio?

Apart from a managed and hosted MCP server, you will get:

  • CodeAct: A dedicated workbench that allows GPT to write its code to handle complex tool chaining. Reduces to-and-fro with LLMs for frequent tool calling.
  • Large tool responses: Handle them to minimise context rot.
  • Dynamic just-in-time access to 20,000 tools across 1000+ other Apps for cross-app workflows. It loads the tools you need, so GPTs aren't overwhelmed by tools you don't need.

How to install Langfuse MCP in Codex

Run the setup command

Run this command in your terminal to add the Composio MCP server to Codex.

Terminal

It will initiate the authentication in a browser window, authorize Codex to access your Composio account.

Composio authentication page

(Optional) Authenticate with OAuth

To authenticate manually, run the login command to open a browser window and authorize Codex to access your Composio account.

bash
codex mcp login composio

Verify the connection

Run codex mcp list to confirm Composio appears as a registered MCP server.

bash
codex mcp list

Codex App

Codex App follows the same approach as VS Code.

  1. Click ⚙️ on the bottom left → MCP Servers → + Add servers → Streamable HTTP:
  2. Fill the header and Key fields with { "x-consumer-api-key" = "ck_*******" }.
  3. The Key is the Composio API key, that you can find on dashboard.composio.dev
  4. Click on Authenticate and authorize Codex to your Composio account and you're all set.
Codex App MCP setup
  1. Restart and verify if it's there in .codex/config.toml
bash
[mcp_servers.composio]
url = "https://connect.composio.dev/mcp"
http_headers = { "x-consumer-api-key" = "ck_*******" }

What is the Langfuse MCP server, and what's possible with it?

The Langfuse MCP server is an implementation of the Model Context Protocol that connects your AI agent and assistants like Claude, Cursor, etc directly to your Langfuse account. It provides structured and secure access to your prompts, traces, evaluations, datasets, experiments, and metrics, so your agent can retrieve prompts, inspect observations, review scores, explore datasets, and analyze performance on your behalf.

  • Prompt retrieval: Have your agent fetch text or chat prompts by name, deployment label, or version, with related prompt dependencies when needed.
  • Trace and observation analysis: Instruct your agent to search generations, spans, events, agent activity, and tool calls to investigate application behavior.
  • Evaluation score management: Let the agent review existing evaluation results or attach new scores to traces, sessions, dataset runs, and specific observations.
  • Dataset and experiment review: Direct your agent to explore available datasets and their items, then review experiments from a chosen time range with metadata and scores.
  • Metrics and evaluation resources: Have your agent query aggregate performance metrics, inspect model pricing definitions, and list annotation queues used for human evaluation.

Conclusion

You've successfully integrated Langfuse with Codex using Composio's MCP server. Now you can interact with Langfuse directly from your terminal, VS Code, or the Codex App using natural language commands.

Key benefits of this setup:

  • Seamless integration across CLI, VS Code, and standalone app
  • Natural language commands for Langfuse operations
  • Managed authentication through Composio
  • Access to 20,000+ tools across 1000+ apps for cross-app workflows
  • CodeAct workbench for complex tool chaining

Next steps:

  • Try asking Codex to perform various Langfuse operations
  • Explore cross-app workflows by connecting more toolkits
  • Build automation scripts that leverage Codex's AI capabilities
TOOLS

Supported Tools

Every Langfuse action and event your agent gets out of the box.

Create Score

Attach an evaluation score to exactly one Langfuse trace, session, or dataset run, optionally narrowing a trace score to an observation.

Get Prompt

Retrieve a Langfuse text or chat prompt by name, deployment label, or exact version, with optional dependency resolution.

List Annotation Queues

List annotation queues configured for human evaluation in the connected Langfuse project.

List Dataset Items

List dataset items, optionally scoped to a dataset, source trace or observation, or historical dataset version.

List Datasets

List datasets available to the connected Langfuse project.

List Experiments

List Langfuse experiments active in a required time range, optionally including metadata and directly attached scores.

List Models

List Langfuse-managed and project-custom model pricing definitions used for usage and cost calculation.

List Observations

Search Langfuse observations such as generations, spans, events, agents, and tool calls, selecting only the field groups needed.

List Scores

Search numeric, boolean, categorical, text, and correction scores with subject and annotation context.

Query Metrics

Run an aggregate Langfuse metrics query over observations or numeric, boolean, or categorical scores.

FAQ

Frequently asked questions

With a standalone Langfuse MCP server, the agents and LLMs can only access a fixed set of Langfuse tools tied to that server. However, with the Composio Tool Router, agents can dynamically load tools from Langfuse and many other apps based on the task at hand, all through a single MCP endpoint.

Yes, you can. Codex fully supports MCP integration. You get structured tool calling, message history handling, and model orchestration while Tool Router takes care of discovering and serving the right Langfuse tools.

Yes, absolutely. You can configure which Langfuse scopes and actions are allowed when connecting your account to Composio. You can also bring your own OAuth credentials or API configuration so you keep full control over what the agent can do.

All sensitive data such as tokens, keys, and configuration is fully encrypted at rest and in transit. Composio is SOC 2 Type 2 compliant and follows strict security practices so your Langfuse data and credentials are handled as safely as possible.

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