> ## Documentation Index
> Fetch the complete documentation index at: https://braintrust.dev/docs/llms.txt
> Use this file to discover all available pages before exploring further.

# Claude Code

> Trace and connect Claude Code to Braintrust from the terminal or the Code tab in the Claude desktop app

[Claude Code](https://code.claude.com/docs/en/overview) is Anthropic's agentic coding tool, available from the terminal and from the Code tab in the Claude desktop app. You can connect it to Braintrust in two ways:

* **Trace Claude Code sessions** to record session, turn, model call, tool, and subagent spans in Braintrust.
* **Connect to Braintrust MCP** to work with Braintrust projects, experiments, logs, and other data from Claude Code.

<Note>
  This guide covers the Claude Code CLI and local Claude Code sessions in the Code tab of the desktop app. Both interfaces use the same tracing plugin and native Claude Code MCP configuration.
</Note>

## Trace Claude Code sessions

The [`trace-claude-code` plugin](https://github.com/braintrustdata/braintrust-claude-plugin) passes your interactions with Claude Code to `bt`, which in turn uses a background process to build and deliver the trace to Braintrust.

Claude Code continues to communicate directly with its model provider, and tracing failures do not stop your Claude Code session.

### Set up tracing

<Note>
  If `trace-claude-code` is already installed, follow [Update the tracing plugin](#update-the-tracing-plugin).
</Note>

<Steps>
  <Step title="Install Claude Code">
    If you haven't already, install the [Claude Code CLI](https://code.claude.com/docs/en/overview) or the [Claude Code desktop app](https://code.claude.com/docs/en/desktop-quickstart).
  </Step>

  <Step title="Install and authenticate bt">
    Follow the [`bt` CLI quickstart](/docs/reference/cli/quickstart) to install `bt`, authenticate, and set your active context.
  </Step>

  <Step title="Enable tracing">
    Before starting Claude Code, run this command in a terminal:

    ```bash theme={"theme":{"light":"github-light","dark":"github-dark-dimmed"}}
    bt trace enable claude --project <your-project>
    ```

    This command:

    * Adds or refreshes the Braintrust [plugin marketplace](https://code.claude.com/docs/en/plugin-marketplaces).
    * Installs (or updates) and enables [`trace-claude-code`](https://github.com/braintrustdata/braintrust-claude-plugin).
    * Writes a Claude-specific tracing config file, normally `~/.claude/braintrust.json`, which records whether tracing is enabled and which project receives traces.

    The tracing file stores settings, not credentials. These settings apply across projects during normal sessions.

    For more information, see [`bt trace enable`](/docs/reference/cli/trace#bt-trace-enable).
  </Step>

  <Step title="Restart Claude Code">
    Exit any running Claude Code CLI or desktop sessions and start a new local session.
  </Step>

  <Step title="Log a test trace">
    Ask Claude Code to do something simple in the terminal or the Code tab in the Claude desktop app. When the session finishes, open your Braintrust project and confirm that the trace appears on the [**<Icon icon="activity" /> Logs**](https://www.braintrust.dev/app/~/logs) page.
  </Step>
</Steps>

### What Braintrust traces

Claude Code traces in Braintrust include:

* Session spans with the session ID, workspace, hostname, username, operating system, Claude Code version, model, and Git repository metadata.
* Turn spans with prompts and final responses.
* Model call spans with prompts, completions, token metrics, and errors.
* Tool spans with inputs, outputs, approval state, and tool names.
* Skill metadata when a turn loads skills.
* Subagent spans nested under the turn that started the subagent.

Every span records its origin as `braintrust.plugin.claude-code`, and the session span records the plugin version in `trace_claude_code_version`.

### Common workflows

<AccordionGroup>
  <Accordion title="Use different tracing settings for one session">
    Use [`bt trace run`](/docs/reference/cli/trace#bt-trace-run) to trace a single Claude Code invocation without changing the saved tracing configuration.

    This workflow launches Claude Code from the terminal.

    To change the saved destination, profile, or organization, rerun [`bt trace enable claude`](/docs/reference/cli/trace#bt-trace-enable) with the corresponding options. Running [`bt switch`](/docs/reference/cli/switch) does not change the saved tracing configuration.

    To add root-span metadata, pass `--additional-metadata '<JSON>'` to `bt trace run` for one invocation or to `bt trace enable` for future sessions. Standard session metadata takes precedence when keys conflict.

    With `bt` v0.19.3 or later, pass `--tag ci --tag release-validation` to either command to [tag session spans](/docs/reference/cli/trace#tag-traces).
  </Accordion>

  <Accordion title="Trace a saved Claude Code session">
    Claude Code stores session transcripts locally. Use [`bt trace import`](/docs/reference/cli/trace#bt-trace-import) to import a past session, even if tracing was not enabled when it ran.

    You can also attach an imported session to an existing span or experiment.
  </Accordion>

  <Accordion title="Resume a Claude Code session">
    When you [resume a Claude Code session](https://code.claude.com/docs/en/cli-reference), new turns are added to its existing Braintrust trace.
  </Accordion>

  <Accordion title="Stop tracing Claude Code sessions">
    Use [`bt trace disable claude`](/docs/reference/cli/trace#bt-trace-disable) to uninstall the tracing plugin and remove its tracing configuration. Saved `bt` profiles and credentials are preserved. Restart Claude Code afterward.
  </Accordion>
</AccordionGroup>

### Update the tracing plugin

To update the plugin, follow these steps:

<Note>
  If `claude plugin list --json` shows `trace-claude-code` earlier than v2.0.1, or `bt --version` shows a version earlier than v0.19.0, follow [Migrate from an older plugin version](#migrate-from-an-older-plugin-version).
</Note>

<Steps>
  <Step title="Update bt">
    Follow the [CLI migration guide](/docs/reference/cli/migrate) to update `bt` to the latest version and complete the applicable migrations.
  </Step>

  <Step title="Update the tracing plugin">
    ```bash theme={"theme":{"light":"github-light","dark":"github-dark-dimmed"}}
    bt trace update claude
    ```

    [`bt trace update`](/docs/reference/cli/trace#bt-trace-update) updates the installed plugin without changing your saved tracing configuration.
  </Step>

  <Step title="Restart and verify Claude Code">
    Restart Claude Code, run a short local session in the CLI or desktop app, and confirm that its trace appears on the [**<Icon icon="activity" /> Logs**](https://www.braintrust.dev/app/~/logs) page in the intended Braintrust project.
  </Step>
</Steps>

### Migrate from an older plugin version

To migrate to the latest version of the `trace-claude-code` plugin, follow these steps:

<Steps>
  <Step title="Inspect your Claude plugins">
    Run this command and find `trace-claude-code@braintrust-claude-plugin`:

    ```bash theme={"theme":{"light":"github-light","dark":"github-dark-dimmed"}}
    claude plugin list --json
    ```

    Record the tracing plugin's starting `version` before updating. If your tracing configuration file exists, also record its profile, organization, project, and any custom tracing settings you want to preserve.

    <Note>
      If the tracing plugin is not installed, follow [Set up tracing](#set-up-tracing).
    </Note>
  </Step>

  <Step title="Install or update bt">
    Check whether `bt` is installed:

    ```bash theme={"theme":{"light":"github-light","dark":"github-dark-dimmed"}}
    bt --version
    ```

    * If the command succeeds, [migrate to the latest version](/docs/reference/cli/migrate) (unless you've already done so).
    * Otherwise, [install `bt`](/docs/reference/cli/quickstart), authenticate, and set organization and project context.
  </Step>

  <Step title="Complete version-specific migration steps">
    <Note>
      Complete each section for a version newer than your starting `trace-claude-code` version, beginning with the oldest. If no sections apply, continue to the next step.
    </Note>

    <AccordionGroup>
      <Accordion title="trace-claude-code v2.0.1">
        <Note>
          Complete this section if you started your migration from a tracing-plugin version earlier than v2.0.1.
        </Note>

        Before v2.0.1, the tracing plugin read settings from Claude's environment. Starting in v2.0.1, it reads a dedicated configuration file written by `bt trace enable claude`.

        If you don't know which Braintrust project has been receiving your traces, find the value of the `BRAINTRUST_CC_PROJECT` variable.

        To find it, look in the `env` object in `~/.claude/settings.json` or the project's `.claude/settings.local.json`, and in your shell configuration. If it is not set, the earlier plugin used the `claude-code` project.
      </Accordion>
    </AccordionGroup>
  </Step>

  <Step title="Apply your tracing settings">
    Run this command with your intended project, using the project you recorded earlier to preserve your destination:

    ```bash theme={"theme":{"light":"github-light","dark":"github-dark-dimmed"}}
    bt trace enable claude --project <your-project>
    ```

    Pass `--profile <profile>` and `--org <organization>` if needed to preserve your tracing account and organization. Otherwise, the command uses your active `bt` context, not your saved tracing settings.

    To preserve metadata from an older plugin's configuration or `BRAINTRUST_ADDITIONAL_METADATA`, pass it explicitly with `--additional-metadata '<JSON>'`. Normal-session hooks do not read metadata from this environment variable.

    The command updates your tracing file, normally `~/.claude/braintrust.json`. Check the following settings in that file:

    * Existing `route.additional_metadata` is preserved unless you pass `--additional-metadata`.
    * Existing `route.tags` is preserved unless you pass `--tag` or set `BRAINTRUST_TAGS`.
    * `route.flush_mode` resets to `fire_and_forget`. Restore its previous value if you customized it.
    * Restore any other custom tracing settings you recorded before updating.
  </Step>

  <Step title="Restart and verify Claude Code">
    Restart Claude Code, run a short local session in the CLI or desktop app, and confirm that its trace appears on the [**<Icon icon="activity" /> Logs**](https://www.braintrust.dev/app/~/logs) page in the intended Braintrust project.
  </Step>

  <Step title="Remove obsolete environment settings">
    <Note>
      Complete this step only if you started with a tracing-plugin version earlier than v2.0.1 and verified that traces reach the intended project in the previous step.
    </Note>

    <Accordion title="Environment settings used before trace-claude-code v2.0.1">
      The tracing plugin now reads its settings from a dedicated configuration file. Environment variables you previously configured for tracing may no longer be needed.

      Check these locations for leftover settings:

      * The `env` object in `~/.claude/settings.json`
      * The `env` object in your project's `.claude/settings.local.json`
      * Your shell configuration

      Remove the variables below if they were used only for tracing. Keep any that other `bt` commands, MCP connections, or integrations still need:

      * `TRACE_TO_BRAINTRUST`
      * `BRAINTRUST_CC_PROJECT`
      * `BRAINTRUST_API_KEY`
      * `BRAINTRUST_API_URL` and `BRAINTRUST_APP_URL`
      * `BRAINTRUST_ORG_NAME`
      * `CC_PARENT_SPAN_ID`, `CC_ROOT_SPAN_ID`, and `CC_EXPERIMENT_ID`
      * `BRAINTRUST_CC_DEBUG`, `BRAINTRUST_ENVIRONMENT_TYPE`, and `BRAINTRUST_ENVIRONMENT_NAME`
    </Accordion>
  </Step>
</Steps>

### Troubleshooting tracing

First, run `bt trace doctor claude`. Then, review the following:

<AccordionGroup>
  <Accordion title="The tracing plugin is missing or disabled">
    Run `claude plugin list` and confirm that `trace-claude-code@braintrust-claude-plugin` is installed and enabled. If it is missing or broken, run:

    ```bash theme={"theme":{"light":"github-light","dark":"github-dark-dimmed"}}
    bt trace enable claude --project <your-project>
    ```

    Restart Claude Code afterward.
  </Accordion>

  <Accordion title="Traces do not appear after setup">
    Opening Claude Code alone does not create a trace. Submit a prompt to verify tracing.

    If Claude Code was running when its plugin or configuration changed, restart it.

    Run `bt trace doctor claude` and confirm that tracing is enabled and routed to the intended project.

    If authentication succeeds but traces do not appear, confirm that your account has [permission to write logs to the selected project](/docs/reference/cli/trace#project-log-permissions).

    For authentication, tracing destination, or endpoint problems, see [`bt trace` troubleshooting](/docs/reference/cli/trace#troubleshooting) and the [CLI migration troubleshooting guide](/docs/reference/cli/migrate#troubleshooting).

    Tracing failures do not interrupt the Claude Code session.
  </Accordion>

  <Accordion title="Claude Code uses an unexpected configuration directory">
    Check whether [`CLAUDE_CONFIG_DIR`](https://code.claude.com/docs/en/env-vars) is set in the environment that launches Claude Code. When it's set, `bt trace enable claude` and the tracing integration use `$CLAUDE_CONFIG_DIR/braintrust.json` instead of `~/.claude/braintrust.json`.

    An explicit `BT_DAEMON_CONFIG` override changes the tracing file path. If you use it, supply the same path when enabling tracing and launching Claude Code.
  </Accordion>

  <Accordion title="Traces use unexpected settings">
    Invocation settings supplied by `bt trace run` take precedence over the saved tracing configuration. For normal sessions, the integration does not use `TRACE_TO_BRAINTRUST`, `BRAINTRUST_CC_PROJECT`, or `BRAINTRUST_ADDITIONAL_METADATA` from the agent's environment to override the saved tracing settings.

    For environment variables accepted by the `bt` commands themselves, see [`bt trace`](/docs/reference/cli/trace).
  </Accordion>

  <Accordion title="bt reports obsolete tracing environment settings">
    `bt trace enable claude` warns when Claude settings contain environment variables used by an earlier tracing plugin.

    <Note>
      Follow step 6, "Remove obsolete environment settings," under [Migrate from an older plugin version](#migrate-from-an-older-plugin-version) to clean up these variables.
    </Note>
  </Accordion>
</AccordionGroup>

## Connect to Braintrust MCP

The Braintrust MCP server lets Claude Code query and update Braintrust data. MCP is configured independently from the tracing plugin.

### Set up the MCP server

<Steps>
  <Step title="Install Claude Code">
    If you haven't already, install the [Claude Code CLI](https://code.claude.com/docs/en/overview) or the [Claude Code desktop app](https://code.claude.com/docs/en/desktop-quickstart).
  </Step>

  <Step title="Add the Braintrust MCP server">
    <Accordion title="Remove the retired Braintrust MCP plugin (if installed)">
      To connect Claude Code to the Braintrust MCP server, Braintrust previously published a `braintrust` plugin. However, the plugin has been retired in favor of Claude Code's native MCP configuration. If you installed the plugin, remove it before configuring the direct connection below.

      Check whether the plugin is still installed:

      ```bash theme={"theme":{"light":"github-light","dark":"github-dark-dimmed"}}
      claude plugin list --json
      ```

      If `braintrust@braintrust-claude-plugin` appears in the list, use its `scope` value to remove it:

      ```bash theme={"theme":{"light":"github-light","dark":"github-dark-dimmed"}}
      claude plugin uninstall braintrust@braintrust-claude-plugin \
        --scope <scope>
      ```

      If it appears at more than one scope, repeat the command for each scope. Keep the marketplace if you use the `trace-claude-code` tracing plugin.
    </Accordion>

    From the terminal, configure Claude Code's connection to the Braintrust MCP server. Choose whether to make it available only in the current project or across all of your projects:

    <Tabs>
      <Tab title="Current project">
        ```bash theme={"theme":{"light":"github-light","dark":"github-dark-dimmed"}}
        claude mcp add --transport http braintrust \
          https://api.braintrust.dev/mcp
        ```

        Claude stores this local-scope configuration in `~/.claude.json` under the current project's path.
      </Tab>

      <Tab title="All projects">
        ```bash theme={"theme":{"light":"github-light","dark":"github-dark-dimmed"}}
        claude mcp add --scope user --transport http braintrust \
          https://api.braintrust.dev/mcp
        ```

        Claude stores this user-scope configuration in `~/.claude.json` and makes it available across your projects.
      </Tab>
    </Tabs>

    Both scopes work in the Claude Code CLI and in local Code-tab sessions of the desktop app. They do not apply to standard Chat or Cowork, which use [connectors](https://support.claude.com/en/articles/11176164).

    These commands add the server but do not authenticate it. See [Authentication](/docs/integrations/developer-tools/mcp#authentication) for API-key setup and [Endpoints](/docs/integrations/developer-tools/mcp#endpoints) for EU and self-hosted URLs.
  </Step>

  <Step title="Authenticate">
    Start the OAuth flow:

    ```bash theme={"theme":{"light":"github-light","dark":"github-dark-dimmed"}}
    claude mcp login braintrust
    ```

    MCP authentication is separate from `bt login`, which authenticates the CLI and tracing integration.
  </Step>

  <Step title="Verify the connection">
    Open or restart Claude Code in the interface you use:

    * **CLI**: Start Claude Code and run `/mcp` to confirm that the Braintrust server is connected.
    * **Code tab**: Start a local session. For local scope, open the project where you ran `claude mcp add`. For user scope, open any project.

    Ask Claude Code to list your recent Braintrust projects and confirm that it uses the Braintrust MCP server.
  </Step>
</Steps>

### Use MCP tools

Once connected, Claude Code can query logs, compare experiments, work with datasets, and use other Braintrust tools. For example:

* "Show me my recent Braintrust experiments."
* "Query the last 10 logged requests with errors."
* "Compare accuracy scores between my two latest experiments."

See [what the Braintrust MCP can do](/docs/integrations/developer-tools/mcp#what-the-mcp-can-do) for more workflows and example prompts.

### Troubleshooting MCP

<AccordionGroup>
  <Accordion title="Braintrust MCP tools do not appear">
    Run `/mcp` and confirm that the Braintrust remote server is registered and connected. Restart Claude Code after adding or changing the server.

    For a local-scope server in the Code tab, confirm that the local session opened the same project where you ran `claude mcp add`.
  </Accordion>

  <Accordion title="MCP authentication or connection fails">
    Run `/mcp` to retry authentication. For authentication methods, regional and self-hosted endpoints, and network requirements, see the [Braintrust MCP guide](/docs/integrations/developer-tools/mcp#connect-your-client).
  </Accordion>
</AccordionGroup>

## Next steps

* **Learn the CLI**: See the full [`bt trace` reference](/docs/reference/cli/trace).
* **Run evaluations**: Follow the [evaluation guide](/docs/evaluate/run-evaluations).
* **Explore MCP tools**: See the [Braintrust MCP tool reference](/docs/integrations/developer-tools/mcp#tools).
* **Browse the source**: View the [coding-agent plugins repository](https://github.com/braintrustdata/braintrust-coding-agent-plugins).