> AI agents: this is one page from PostHog's docs. Full index of Markdown docs for LLMs: https://posthog.com/llms.txt

# Linking LangSmith as a source

Canonical URL: https://posthog.com/docs/data-pipelines/sources/langsmith

> **Cloud region:** This page uses US Cloud hosts. For an EU Cloud project, use `https://eu.posthog.com` instead of `https://us.posthog.com` or `https://app.posthog.com` (app host for links).

## On this page

- [Prerequisites](#prerequisites)
- [Adding a data source](#adding-a-data-source)
- [Sync modes](#sync-modes)
- [Configuration](#configuration)
- [Supported tables](#supported-tables)
- [Troubleshooting](#troubleshooting)

![](https://res.cloudinary.com/dmukukwp6/image/upload/texture_tan_9608fcca70)

![](https://res.cloudinary.com/dmukukwp6/image/upload/texture_tan_dark_a92b0e022d)

Let AI connect your sources for you

Skip the manual setup — run this in your project and the wizard auto-detects your databases and APIs and connects them to PostHog.

`npx @posthog/wizard warehouse`

![PostHog Wizard hedgehog](https://res.cloudinary.com/dmukukwp6/image/upload/wizard_3f8bb7a240.png)

![](https://res.cloudinary.com/dmukukwp6/image/upload/wizard_3f8bb7a240.png)Let AI connect your sources for you

Sync your LangSmith LLM observability data – traces and runs, tracing projects, datasets, examples, feedback, annotation queues, conversation threads, workspaces, and annotation queue runs – into the PostHog data warehouse, so you can join LLM behavior and cost with your product analytics.

## Prerequisites

You need a LangSmith account with access to the workspace you want to sync. Any member can create a personal access token; workspace-scoped service keys need workspace admin access.

## Adding a data source

1.  In PostHog, go to the [Sources tab](https://app.posthog.com/data-management/sources) of the data pipeline section.
2.  Click **\+ New source** and click **Link** next to this source.
3.  Enter your credentials (see [Configuration](#configuration) below) and click **Next**.
4.  Select the tables you want to sync, choose a sync method and frequency, then click **Import**.

Once the syncs are complete, you can start querying this data in PostHog.

You need a LangSmith API key. Create one in your [LangSmith settings](https://smith.langchain.com/settings) under **API Keys**.

Leave the **Host** field blank if your account is on the US cloud (`api.smith.langchain.com`). Set it to `https://eu.api.smith.langchain.com` for EU-region accounts, or to your own host for self-hosted LangSmith deployments.

## Sync modes

Each table can be synced in one of several modes, depending on what the source supports:

-   **Webhook** (when available) – the source pushes changes to PostHog in real time. Fastest freshness, lowest ongoing cost, and the only mode that reliably captures updates and deletes.
-   **Incremental** – only new or updated rows are synced on each run, using a cursor field (such as an `updated_at` timestamp). Cheaper than a full refresh, but deletes aren't captured.
-   **Append only** – new rows are appended using a cursor field; existing rows are never updated. Ideal for immutable, append-only tables like event logs.
-   **Full refresh** – the whole table is reloaded on every sync. Use it when a table has no reliable cursor or when you need deletions reflected.

See [sync methods](https://posthog.com/docs/data-pipelines/sources.md#sync-methods) for a full explanation of how each mode works and how to choose between them.

The `runs` table can be large. Use incremental sync for it: runs are filtered server-side by `start_time`, and the first incremental sync only pulls the last 365 days. Each incremental sync also re-reads a short trailing window so runs that finish (or receive feedback) after they were first synced get updated.

LangSmith rate-limits its run query API, so very large workspaces may see the initial `runs` backfill take a while.

## Configuration

| Option | Type | Required |
| --- | --- | --- |
| `API key` | password | Yes |
| `Host` | text | No |

## Supported tables

| Table | Description | Sync method | Incremental field | Primary key |
| --- | --- | --- | --- | --- |
| `runs` | Traces and their nested spans (LLM calls, chains, tools) across every tracing project. The first incremental sync only pulls the last 365 days | Incremental, Full refresh | start\_time | id |
| `projects` | Tracing projects (called sessions in the LangSmith API) | Full refresh | — | id |
| `datasets` | Datasets used for testing and evaluating LLM applications: collections of example inputs and expected outputs. | Full refresh | — | id |
| `examples` | Examples (input/output pairs) belonging to datasets, used as test cases and evaluation ground truth. | Full refresh | — | id |
| `feedback` | Human and programmatic feedback scores attached to runs, e.g. thumbs up/down, correctness scores, or evaluator results. | Incremental, Full refresh | created\_at | id |
| `annotation_queues` | Annotation queues used to collect human feedback on runs, with reviewer and reservation settings. | Full refresh | — | id |
| `annotation_queue_runs` | Runs added to each annotation queue, with the queue item's review state. Joins annotation\_queues to runs. | Full refresh | — | queue\_id, queue\_run\_id |
| `threads` | Conversation threads in each tracing project, with stats over the last 365 days | Full refresh | — | project\_id, thread\_id |
| `workspaces` | Workspaces (called tenants in the LangSmith API) the API key can access. Resolves the tenant\_id on other tables. | Full refresh | — | id |

## Troubleshooting

If the source fails to connect, check that the API key is valid and that the **Host** field matches your LangSmith region – an EU-region key against the default US host returns a `401` error.

If your sync is failing or data looks wrong, see the [Data warehouse troubleshooting guide](https://posthog.com/docs/data-warehouse/troubleshooting.md). If that doesn't help, [contact support](https://us.posthog.com/#panel=support%3Asupport%3Adata_warehouse%3A%3Atrue) – we're happy to help.