# Reported issues for Langfuse MCP

Pod holds 10 of 10 GitHub reports that passed its relevance review. This can include external user reports, maintainer-confirmed bugs, and concrete feature gaps. Treat them as evidence to inspect, not a count of distinct defects.

Back to [Langfuse MCP](/mcp/langfuse-mcp).

## Most discussed

### multi-project support via per-request credentials in HTTP headers

### Problem / Use Case

Currently the MCP server requires LANGFUSE_PUBLIC_KEY and LANGFUSE_SECRET_KEY to be set at startup. This means each Langfuse project requires a separate server instance — a separate Docker container, a separate MCP
  entry in Claude Code config, etc. For teams or individuals working with 10–30 projects this becomes unmanageable.
  
  Desired behavior
  
  One server instance should be able to serve multiple Langfuse projects. Credentials for a specific project should be…

[Read the thread](https://github.com/avivsinai/langfuse-mcp/issues/48) · 2026-05-13 · closed · outside contributor · 2 comments

### Allow configurable timeout value

When I run the tool with e.g. following input:

```
{
  "session_id": "<REDACTED>",
  "include_observations": true,
  "output_mode": "compact"
}
```

I get the following output: `Error executing tool get_session_details: The read operation timed out`. It's the same for every other tool I kept trying. I'm using the default host i.e. the cloud one

Stack trace:

```
2025-12-27 07:21:48 - mcp.server.lowlevel.server - INFO - Processing request of type CallToolRequest
2025-12-27 07:21:53 -…

[Read the thread](https://github.com/avivsinai/langfuse-mcp/issues/5) · 2025-12-27 · closed · external user · 2 comments

### Profile-based multi-project support for stdio (`--profile`)

Split out from #48 / #49, which handle the HTTP multi-tenant (shared Docker / team) path.

For the common local stdio case (Claude Code / Codex / Cursor), support multiple Langfuse projects via named profiles — e.g. `langfuse-mcp --profile prod`, backed by a local profiles config. Users register one MCP server per project and let the MCP client route by server name, with no HTTP/auth surface.

This is intentionally separate from the per-request HTTP credential path in #48/#49 so the two product…

[Read the thread](https://github.com/avivsinai/langfuse-mcp/issues/54) · 2026-05-29 · open · 1 comment

### Error executing tool get_session_details

Error executing tool get_session_details: status_code: 500, body: {'message': 'Internal Server Error', 'error': "Cannot parse DateTime: value 0 cannot be parsed as DateTime64(3) for query parameter 'dateTimeFiltercutvv'. "}

[Read the thread](https://github.com/avivsinai/langfuse-mcp/issues/13) · 2026-02-08 · closed · external user · 1 comment

### Documentation: Incorrect command syntax for `claude mcp add` in README

## Issue Description

The installation command in the README has incorrect syntax that causes an error when users try to add the Langfuse MCP server.

## Current Documentation

The README currently shows:
```bash
claude mcp add \
  --scope project \
  --env LANGFUSE_PUBLIC_KEY=pk-... \
  --env LANGFUSE_SECRET_KEY=sk-... \
  --env LANGFUSE_HOST=https://cloud.langfuse.com \
  langfuse -- uvx --python 3.11 langfuse-mcp
```

## Error Encountered

When running this command, users get:
```
Invalid…

[Read the thread](https://github.com/avivsinai/langfuse-mcp/issues/12) · 2026-01-27 · closed · external user · 1 comment

### Dataset-run tools use endpoints Langfuse Cloud removes on Nov 16 (move to experiments API)

Split out from #83. #84 (observations v2) and #85 (scores v3) cover the trace, session, observation and score reads. The dataset-run tools still call endpoints that Langfuse Cloud removes on **2026-11-16** ([migration FAQ](https://langfuse.com/faq/all/deprecated-api-migration)):

| Tool | Current call | Replacement |
|---|---|---|
| `list_dataset_runs` | `GET /datasets/{name}/runs` | `GET /experiments` |
| `get_dataset_run` | `GET /datasets/{name}/runs/{runName}` | `GET /experiments` + `GET…

[Read the thread](https://github.com/avivsinai/langfuse-mcp/issues/86) · 2026-09-25 · closed · 0 comments

### Trace, session and observation reads use the endpoints Langfuse Cloud removes on Nov 16

Langfuse Cloud turns off `GET /api/public/traces`, `/traces/{id}`, `/sessions` and the v1 `/observations` endpoints on 2026-11-16 (after that they return 404): https://langfuse.com/faq/all/deprecated-api-migration

0.11.0 with langfuse 4.x still goes through all of them:

- `_list_traces` -> `api.trace.list` ([__main__.py#L699](https://github.com/avivsinai/langfuse-mcp/blob/2abb3fb68e1dcd19f05b3176ae1f4f89d6a80d2c/langfuse_mcp/__main__.py#L699))
- `_get_trace` -> `api.trace.get`…

[Read the thread](https://github.com/avivsinai/langfuse-mcp/issues/83) · 2026-09-25 · closed · outside contributor · 0 comments

### `fetch_observations` type filter allows 3 of the 10 Langfuse observation types, TOOL and AGENT observations are invisible

**Describe the bug**

`fetch_observations` types its `type` filter as `Literal["SPAN", "GENERATION", "EVENT"]` (`langfuse_mcp/__main__.py`, around line 1717 on main), and the helper tools pass `obs_type="SPAN"` hard-coded. Langfuse's `ObservationType` has ten members, and the observations API accepts all of them (`GET /api/public/observations?type=TOOL` and `?type=AGENT` return 200 against cloud). Every tool call and agent step written by the current instrumentations lands as `TOOL` / `AGENT`,…

[Read the thread](https://github.com/avivsinai/langfuse-mcp/issues/77) · 2026-09-07 · closed · outside contributor · 0 comments

## Most recent

### `placeholder` creation/edition missing for Chat Prompts via Langfuse MCP

**Describe the bug**
The `createChatPrompt` MCP tool (langfuse-mcp server) cannot create "placeholder" messages in chat prompts.
Its input schema for `prompt` items only allows `{role: string, content: string}` (both required, `additionalProperties: false`), but Langfuse chat prompts support a distinct placeholder message shape `{type: "placeholder", name: "<variable>"}` that we use to inject images. Since the tool schema has no way to express this shape, any MCP client is unable to add, edit,…

[Read the thread](https://github.com/avivsinai/langfuse-mcp/issues/70) · 2026-08-07 · closed · external user · 0 comments

### mcp 2.0.0 breaks startup: No module named 'mcp.server.fastmcp'

Fresh install via uvx currently fails to start:

```
$ uvx langfuse-mcp
Traceback (most recent call last):
  File ".../bin/langfuse-mcp", line 6, in <module>
    from langfuse_mcp.__main__ import main
  File ".../site-packages/langfuse_mcp/__main__.py", line 30, in <module>
    from mcp.server.fastmcp import Context, FastMCP
ModuleNotFoundError: No module named 'mcp.server.fastmcp'
```

langfuse-mcp 0.10.0 declares `mcp[cli]>=1.6.0` with no upper bound, so uv resolves the freshly released mcp…

[Read the thread](https://github.com/avivsinai/langfuse-mcp/issues/67) · 2026-08-04 · closed · external user · 0 comments

The remaining reports are on [the project's issue tracker](https://github.com/avivsinai/langfuse-mcp/issues).