# LangSmith

> Connect LangSmith so Ace can read your AI workflow runs and traces during investigations.

Source: https://tryace.dev/docs/integrations/langsmith

Ace reads LangSmith to see what your AI workflows did around an incident, including which runs failed, how long they took and what their child spans did.

| | |
| --- | --- |
| Category | AI workflow traces, latency, cost and feedback |
| Ace reads | Projects, root runs, failed runs, child runs (spans) and project feedback stats |
| Ace can change | Nothing (read-only) |
| Opens incidents | No |
| Setup | Settings form |

## What Ace reads

When you connect, Ace lists the projects the API key can see, with their stats. During an investigation it reads:

- Project runs in the incident window: root runs, failed root runs, runs that match the incident, and their child spans.
- The child runs (spans) of one trace, in start order.

**Workspace ID** limits Ace to one workspace, and **Project allowlist** limits it to specific projects.

## What Ace can change

Nothing.

## What opens an incident

Nothing. Ace uses LangSmith as evidence only.

## Before you start

- The **admin** role in Ace.
- A LangSmith API key that can list projects.
- LangSmith cloud in the US or EU works as is. A dedicated or private base URL goes in as a custom endpoint, which must be reachable over HTTPS from Ace's cloud.

## Credentials and permissions

| Credential | Where to create it | Permissions | Why Ace needs it |
| --- | --- | --- | --- |
| API key | LangSmith: **Settings** > **API Keys** > **Create API Key** | Read access to the projects Ace should see. A service key scoped to your workspace works best. On Enterprise, give it the **Workspace Viewer** role so it can only read. | List projects and read runs. |

## Set up

1. Create the API key in LangSmith.
2. In Ace, go to **Settings** > **Data sources** > **LangSmith**.
3. Fill in the form:
   - **Endpoint**: **US (https://api.smith.langchain.com)** or **EU (https://eu.api.smith.langchain.com)**, matching your workspace's region. Choose **Custom** only if LangSmith gave you a dedicated or private base URL, which must use HTTPS.
   - **API key**: starts with `lsv2_`.
   - **Workspace ID** (optional): the workspace Ace should use, if the key can access several. Find it in LangSmith under **Settings** > **General**.
   - **Project allowlist** (optional): one project per line. Leave it blank to let Ace use every project the key can read.
4. Choose **Connect LangSmith**. Ace validates the key first, and if a check fails it shows the error and doesn't connect.

To change the configuration, choose **Update credentials**, then **Save and revalidate**. Ace replaces the stored configuration, revalidates and refreshes discovery.

## Confirm it's working

The panel shows **Connected**, and the discovery panel lists your projects. Two validation errors come up most often:

- "No LangSmith projects were visible to this API key. If this is an org-scoped key, add the workspace ID."
- "No LangSmith projects matched the configured project allowlist." Check the names in **Project allowlist**.

## Disconnect

In Ace, go to **Settings** > **Data sources** > **LangSmith** and choose **Disconnect**. In LangSmith, delete the key under **Settings** > **API Keys**.

## Next steps

- [Logfire](https://tryace.dev/docs/integrations/logfire): add application logs and traces.
- [How Ace works](https://tryace.dev/docs/concepts/how-ace-works): how evidence feeds an investigation.
- [Security and data](https://tryace.dev/docs/security/security-and-data): what Ace stores.