Web Callouts

Web Callouts let project members trigger a configured backend HTTP request from a trace, observation, or session in the Langfuse UI. Use them to connect debugging workflows to internal tools, support systems, incident workflows, or custom investigation services.

Unlike prompt webhooks, Web Callouts are manually triggered from the UI. Langfuse sends the request synchronously from the backend when the user clicks the action.

Configure a Web Callout

Open Project Settings > Integrations > Web Callouts and create a callout endpoint. You need integrations:CRUD permissions. Callouts are configured per project and can be invoked by all users in a project.

Configure:

• Name: shown in the action menu, for example Open in Support Tool.
• URL: HTTP or HTTPS endpoint that accepts POST requests. Custom ports are supported.
• Success toast message: shown after your endpoint returns a successful response.
• Enabled: disabled callouts are hidden from the action menu.
• Request headers: optional static headers, for example Authorization: Bearer <token>.

Trigger a Web Callout

After setup, users with project read access can trigger the callout from:

• The action menu on trace details.
• The action menu on observation details.
• The session details header.

Langfuse sends the request immediately when the user clicks the action. The UI shows a success toast only after your endpoint returns a 2xx response. The request times out after 5 seconds. Calls will not be retried.

Request Payload

Langfuse sends a JSON POST request with this structure:

{
  "version": 1,
  "items": [
    {
      "projectId": "project-id",
      "traceId": "trace-id",
      "observationId": null,
      "sessionId": "session-id"
    }
  ]
}

Note: all ID fields except for the projectId are nullable. Langfuse validates that the trace, observation, and session belong to the project before sending the request.

Endpoint Requirements

Your endpoint must:

• Accept POST requests with Content-Type: application/json.
• Return any HTTP 2xx status within 5 seconds.

Langfuse treats non-2xx responses, network errors, invalid URLs, and timeouts as failed callouts and shows an error toast.

Web Callouts are not retried and Langfuse does not keep a delivery log.

Authentication and Headers

You can configure static request headers for authentication, for example Authorization or X-API-Key. Header values are encrypted at rest and are sent from the Langfuse backend. When editing an existing header without changing its name, leaving the value empty keeps the stored encrypted value.

Langfuse sets Content-Type: application/json and User-Agent: Langfuse/1.0 automatically. The following header names cannot be configured: content-length, content-type, cookie, and host.