Mastra LLM analytics installation

  1. Install the PostHog SDK

    Required

    Setting up analytics starts with installing the PostHog SDK.

    npm install @posthog/ai posthog-node

  2. Install Mastra

    Required

    Install Mastra and a model provider SDK. Mastra uses the Vercel AI SDK under the hood, so you can use any Vercel AI-compatible model provider.

    npm install @mastra/core @ai-sdk/openai
    Proxy note

    These SDKs do not proxy your calls. They only fire off an async call to PostHog in the background to send the data. You can also use LLM analytics with other SDKs or our API, but you will need to capture the data in the right format. See the schema in the manual capture section for more details.

  3. Initialize PostHog and wrap your model

    Required

    Initialize PostHog with your project API key and host from your project settings, then use withTracing from @posthog/ai to wrap the model you pass to your Mastra agent.

    import { Agent } from "@mastra/core/agent";
    import { PostHog } from "posthog-node";
    import { withTracing } from "@posthog/ai";
    import { createOpenAI } from "@ai-sdk/openai";
    

    const phClient = new PostHog(
      '<ph_project_api_key>',
      { host: 'https://us.i.posthog.com' }
    );
    

    const openaiClient = createOpenAI({
      apiKey: 'your_openai_api_key',
      compatibility: 'strict'
    });
    

    const agent = new Agent({
      name: "my-agent",
      instructions: "You are a helpful assistant.",
      model: withTracing(openaiClient("gpt-4o"), phClient, {
        posthogDistinctId: "user_123", // optional
        posthogTraceId: "trace_123", // optional
        posthogProperties: { conversationId: "abc123" }, // optional
        posthogPrivacyMode: false, // optional
        posthogGroups: { company: "companyIdInYourDb" }, // optional
      }),
    });

    You can enrich LLM events with additional data by passing parameters such as the trace ID, distinct ID, custom properties, groups, and privacy mode options.

  4. Use your Mastra agent

    Required

    Now, when your Mastra agent makes LLM calls, PostHog automatically captures an $ai_generation event for each one.

    const result = await agent.generate("What is the capital of France?");
    

    console.log(result.text);
    

    phClient.shutdown();

    Note: If you want to capture LLM events anonymously, don't pass a distinct ID to the request. See our docs on anonymous vs identified events to learn more.

    You can expect captured $ai_generation events to have the following properties:

    PropertyDescription
    $ai_modelThe specific model, like gpt-5-mini or claude-4-sonnet
    $ai_latencyThe latency of the LLM call in seconds
    $ai_time_to_first_tokenTime to first token in seconds (streaming only)
    $ai_toolsTools and functions available to the LLM
    $ai_inputList of messages sent to the LLM
    $ai_input_tokensThe number of tokens in the input (often found in response.usage)
    $ai_output_choicesList of response choices from the LLM
    $ai_output_tokensThe number of tokens in the output (often found in response.usage)
    $ai_total_cost_usdThe total cost in USD (input + output)
    [...]See full list of properties

  5. Verify traces and generations

    Recommended
    Confirm LLM events are being sent to PostHog

    Let's make sure LLM events are being captured and sent to PostHog. Under LLM analytics, you should see rows of data appear in the Traces and Generations tabs.


    LLM generations in PostHog
    Check for LLM events in PostHog

  6. Next steps

    Recommended

    Now that you're capturing AI conversations, continue with the resources below to learn what else LLM Analytics enables within the PostHog platform.

    ResourceDescription
    BasicsLearn the basics of how LLM calls become events in PostHog.
    GenerationsRead about the $ai_generation event and its properties.
    TracesExplore the trace hierarchy and how to use it to debug LLM calls.
    SpansReview spans and their role in representing individual operations.
    Anaylze LLM performanceLearn how to create dashboards to analyze LLM performance.

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