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Codex is OpenAI’s coding agent. You can connect it to Braintrust in two ways:
  • Trace Codex 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 Codex.

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Trace Codex sessions

The trace-codex plugin passes your interactions with Codex to bt, which in turn uses a background process to build and deliver the trace to Braintrust. Codex continues to communicate directly with its model provider, and tracing failures do not stop your Codex session.

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Set up tracing

If trace-codex is already installed, follow Update the tracing plugin.
1

Install Codex

If you haven’t already, install the Codex CLI. The tracing hooks require Bash, including on Windows.
2

Install and authenticate bt

Follow the bt CLI quickstart to install bt, authenticate, and set your active context.
3

Enable tracing

Before starting Codex, run this command in a terminal:
This command:
  • Adds or refreshes the Braintrust plugin marketplace.
  • Installs (or updates) and enables trace-codex.
  • Writes ~/.codex/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.
4

Restart Codex and approve the plugin's hooks

Restart Codex, then run /hooks and trust the Braintrust hook definition. Codex does not run plugin hooks until you trust them.
5

Log a test trace

Ask Codex to do something simple. When the session finishes, open your Braintrust project and confirm that the trace appears on the Logs page.

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What Braintrust traces

Codex traces in Braintrust include:
  • Session spans with the working directory, model, permission mode, and Git repository metadata.
  • Turn spans with prompts and final responses.
  • Model call spans reconstructed from the session transcript, with conversation input, response output, and available token metrics.
  • Tool spans with inputs, outputs, permission requests, and skill loads.
  • Subagent spans nested under the turn that started the subagent.
  • Compaction spans for context compactions, with a nested model span for the compaction call.
Every span records its origin as braintrust.plugin.codex.

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Common workflows

Use bt trace run to trace a single Codex invocation without changing the saved tracing configuration.This workflow launches Codex from the terminal.To change the saved destination, profile, or organization, rerun bt trace enable codex with the corresponding options. Running bt 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.
Codex stores session transcripts locally. Use 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.
When you resume a Codex session, new turns are added to its existing Braintrust trace.
Use bt trace disable codex to uninstall the tracing plugin and remove its tracing configuration. Saved bt profiles and credentials are preserved. Restart Codex afterward.

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Update the tracing plugin

To update the plugin, follow these steps:
If codex plugin list --json shows trace-codex earlier than v1.0.1, or bt --version shows a version earlier than v0.19.0, follow Migrate from an older plugin version.
1

Update bt

Follow the CLI migration guide to update bt to the latest version and complete the applicable migrations.
2

Update the tracing plugin

bt trace update updates the installed plugin without changing your saved tracing configuration.
3

Restart and verify Codex

Restart Codex and trust the updated Braintrust hook through /hooks if prompted. Run a short session and confirm that its trace appears on the Logs page in the intended Braintrust project.

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Migrate from an older plugin version

To migrate to the latest version of the trace-codex plugin, follow these steps:
1

Inspect your Codex plugins

Run this command and find trace-codex@braintrust-codex-plugins:
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.
If the tracing plugin is not installed, follow Set up tracing.
2

Install or update bt

Check whether bt is installed:
3

Complete version-specific migration steps

Complete each section for a version newer than your starting trace-codex version, beginning with the oldest. If no sections apply, continue to the next step.
Complete this section if you started your migration from a tracing-plugin version earlier than v1.0.1.
Before v1.0.1, the tracing plugin read settings from its own config.json and environment variables. Starting in v1.0.1, it reads a dedicated configuration file written by bt trace enable codex, and bt handles authentication.Find the project that received your traces before updating. In v1.0.0, the settings take precedence in this order:
  1. project in ~/.codex/plugins/data/trace-codex-braintrust-codex-plugins/config.json.
  2. BRAINTRUST_PROJECT in your shell environment.
  3. BRAINTRUST_DEFAULT_PROJECT in your shell environment.
  4. The default project, codex.
In v0.1.0 and earlier, environment variables took precedence over the file instead. If both were set, use the project that actually received your traces.If you configured a different plugin data directory with BRAINTRUST_EVENT_SERVER_LOG_DIR, look for config.json there instead.Also record settings you want to preserve:
  • Extra root-span metadata from additionalMetadata in the old file or BRAINTRUST_ADDITIONAL_METADATA.
  • Turn-end flushing from flushOnTurnEnd in the old file or BRAINTRUST_FLUSH_ON_TURN_END.
  • Deployment endpoints from apiUrl and appUrl in the old file, or BRAINTRUST_API_URL and BRAINTRUST_APP_URL. Configure the appropriate deployment when you authenticate with bt.
4

Apply your tracing settings

Run this command with your intended project, using the project you recorded earlier to preserve your destination:
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 ~/.codex/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.
5

Restart and verify Codex

Restart Codex and trust the updated Braintrust hook through /hooks if prompted. Run a short session and confirm that its trace appears on the Logs page in the intended Braintrust project.
6

Remove obsolete settings

Complete this step only if you started with a tracing-plugin version earlier than v1.0.1 and verified that traces reach the intended project in the previous step.
The tracing plugin now reads its settings from a dedicated configuration file. Environment variables and plugin settings you previously configured for tracing may no longer be needed.Check these locations for leftover settings:
  • Your shell configuration
  • ~/.codex/plugins/data/trace-codex-braintrust-codex-plugins/config.json, or the custom plugin data directory you previously configured
Remove the settings below if they were used only for tracing. Keep any that other bt commands, MCP connections, or integrations still need:To attach an imported session to an existing span or experiment, use bt trace import instead of the old parent-span settings.

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Troubleshooting tracing

First, run bt trace doctor codex. Then, review the following:
Run codex plugin list --json and confirm that trace-codex@braintrust-codex-plugins is installed and enabled. If it is missing or broken, run:
Restart Codex afterward and trust the Braintrust hook through /hooks.
If Codex was running when its plugin or configuration changed, restart it. Confirm that Bash and bt are available to the process that launches Codex, and that you trusted the Braintrust hook through /hooks.Run bt trace doctor codex 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.For authentication, tracing destination, or endpoint problems, see bt trace troubleshooting and the CLI migration troubleshooting guide.Tracing failures do not interrupt the Codex session.
bt trace run codex rejects --dangerously-bypass-hook-trust because it conflicts with the tracing hook managed by bt. Remove the option from the managed command.If an automation requires the option, run Codex directly with the installed tracing plugin instead. Bypass hook trust only when you control and trust every enabled hook.
The tracing file remains at ~/.codex/braintrust.json even when CODEX_HOME changes Codex’s own configuration directory.An explicit BT_DAEMON_CONFIG override changes the tracing file path. If you use it, supply the same path when enabling tracing and launching Codex.
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_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.

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Connect to Braintrust MCP

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

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Set up the MCP server

1

Install Codex

If you haven’t already, install the Codex CLI.
2

Add the Braintrust MCP server

To connect Codex to the Braintrust MCP server, Braintrust previously published a braintrust plugin. However, the plugin has been retired in favor of Codex’s native MCP configuration. If you installed the plugin, remove it before configuring the direct connection below.Check whether the plugin is still installed:
If braintrust@braintrust-codex-plugins appears in the installed plugins, remove it:
Keep the marketplace if you use the trace-codex tracing plugin.
From the terminal, configure Codex’s connection to the Braintrust MCP server:
See Authentication for API-key setup and Endpoints for EU and self-hosted URLs.
3

Authenticate

Complete the browser sign-in if Codex starts an OAuth flow when you add the server. Otherwise, start it with:
MCP authentication is separate from bt login, which authenticates the CLI and tracing integration.
4

Verify the connection

Open or restart Codex and run /mcp to confirm that the Braintrust server is connected. Ask Codex to list your recent Braintrust projects and confirm that it uses the Braintrust MCP server.

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Use MCP tools

Once connected, Codex 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 for more workflows and example prompts.

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Troubleshooting MCP

Run /mcp and confirm that the Braintrust remote server is registered and connected. Restart Codex after adding or changing the server.
Run codex mcp login braintrust to retry OAuth authentication. If you previously configured API-key authentication, remove bearer_token_env_var from the Braintrust server’s entry in your Codex configuration before switching to OAuth.For authentication methods, regional and self-hosted endpoints, and network requirements, see the Braintrust MCP guide.

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Next steps