posthog/setting-up-a-custom-rest-source

Setting up a Custom REST source

A Custom source imports any HTTP REST API into queryable warehouse tables from a JSON manifest — no per-source Python. The manifest is a RESTAPIConfig: the same shape that powers PostHog's built-in REST connectors (Intercom, Attio, Sentry, …), so the generic REST engine handles auth, pagination, JSONPath record extraction, and incremental cursors for you. Your job is to author a correct manifest and prove it against live data before creating the source.

This is an alpha capability. Caps: at most 50 resources per manifest, and at most 5 Custom sources per project.

When to use this skill

• The user wants to import an API that has no built-in connector — an internal service, a niche SaaS, a public API — and can give you its docs URL or describe its endpoints.
• The user explicitly asks for a "custom REST source", "custom source manifest", or to "build a connector from docs".

A Custom source is the fallback — only correct when no native connector fits. PostHog ships hundreds of native connectors, far more than could be listed here, so never assume an API has no built-in — most well-known SaaS apps and databases do, and guessing wrong misroutes them into a hand-authored manifest that duplicates a battle-tested connector. Step 0 below makes you check the registry before drafting anything; if a native connector matches, hand off to setting-up-a-data-warehouse-source instead.

The grammar

Read references/manifest-reference.md before drafting — it is the full RESTAPIConfig field reference (auth types, the six paginators, incremental cursors, parent/child fan-out) with worked examples for each. Draft the manifest from that grammar; don't guess field names.

The skeleton:

{
  "client": {
    "base_url": "https://api.example.com/v1",
    "auth": { "type": "bearer" }
  },
  "resources": [
    {
      "name": "users",
      "primary_key": "id",
      "endpoint": {
        "path": "/users",
        "data_selector": "data",
        "paginator": { "type": "json_response", "next_url_path": "next" },
        "incremental": { "cursor_path": "updated_at", "start_param": "since" }
      }
    }
  ]
}

Secrets never go inline in the manifest. manifest_json holds only the non-secret structure. The credential travels in a separate payload key chosen by the manifest's client.auth.type: auth_token (bearer), auth_api_key (api_key), auth_password (http_basic), or auth_oauth2_client_secret for oauth2 (plus auth_oauth2_refresh_token for the refresh-token grant only). The engine injects it at run time, and PostHog redacts it from every response. Putting a token inline is rejected at validation.

Available tools

| Tool | Purpose | | ---------------------------------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------ | | external-data-sources-wizard | List every native source type PostHog supports. Run this first (Step 0) to check whether the target API already has a built-in connector before drafting a manifest. | | external-data-sources-db-schema | Validate the manifest + credential and list the resources (tables) it exposes, with detected primary keys and incremental cursors. This is the validate-and-list step. | | external-data-sources-preview-resource | Read a small live sample of rows for one resource — verify data_selector / primary_key / cursor_path against real data before creating anything. | | data-warehouse-source-setup | Create the source. Enables all manifest resources with sync defaults in one call. | | external-data-sources-create | Advanced create — lets the user hand-pick which resources sync via a schemas array. | | external-data-schemas-list | After creation, watch per-table sync status. |

Workflow

Step 0 — Check for a native connector first

Before drafting anything, call external-data-sources-wizard to list the native source types and check whether the target API is among them, matching on the service name. A Custom source is the fallback for APIs with no native connector; do not skip this check on the assumption that a well-known API isn't supported — most are.

If a native connector matches, stop and tell the user the built-in path is simpler and battle-tested (it handles auth, pagination, schema, and incremental sync for you), and hand off to setting-up-a-data-warehouse-source. Only continue with this skill when the user has no matching native connector, or explicitly wants to exercise the custom REST path despite one existing.

Step 1 — Gather the API shape

Get either a docs URL (fetch it and read the auth scheme, the list endpoints, their response envelopes, and any pagination) or a natural-language description of the endpoints. You need, per resource you'll import:

• the path (relative to a common base_url) and method (GET, or POST for query-style read endpoints),
• the auth scheme (bearer token / API key in header or query / HTTP basic / OAuth2 with a customer-owned client — client_credentials or a pre-obtained refresh token; the interactive authorization_code flow is not supported),
• the record path — where the array of records sits in the JSON response (e.g. data, results, items),
• how the API paginates (next-URL, link header, cursor, offset, page number, or single page),
• a primary key field, and
• optionally an incremental cursor field (updated_at-style) so re-syncs only fetch new/changed rows.

Ask the user for the credential value, but tell them you'll only ever place it in the auth_* payload key, never in the manifest.

Step 2 — Draft the manifest

Author the RESTAPIConfig from references/manifest-reference.md. Match the auth block to the scheme, pick the paginator that matches the docs, set data_selector to the record path, and add an incremental block when the API has an updated_at-style cursor and a matching query param. For an endpoint whose rows must be fetched per parent (e.g. /forms/{form_id}/responses), use a parent/child resolve param — see the fan-out example. Keep it to one level of nesting.

Step 3 — Validate and list resources

Call external-data-sources-db-schema with { source_type: "Custom", manifest_json: "<stringified manifest>", auth_token: "<credential>" }. The credential key is not literally auth_* — use the one for your auth type: auth_token (bearer), auth_api_key (api_key), auth_password (http_basic), or auth_oauth2_client_secret (+ auth_oauth2_refresh_token for the refresh-token grant). It validates the manifest structure, the fan-out graph, and the credential (a bounded live probe), then returns one table entry per resource with detected_primary_keys and incremental_fields. If it returns a 400, the message is plain English (e.g. resources[0].endpoint.path: must not be empty) — fix the manifest and retry. Loop here until it validates.

Step 4 — Test-read each resource

For each resource, call external-data-sources-preview-resource with { source_type: "Custom", payload: { manifest_json, auth_token }, resource_name: "<name>", limit: 10 } (the auth_token key varies by auth type, as in Step 3). It returns up to limit real rows plus the inferred columns. Check that:

• data_selector is right — rows are the records you expect, not a wrapper object. If rows looks like [{ "data": [...] }] you pointed at the envelope, not the array; fix data_selector.
• primary_key exists in the rows and is unique.
• the incremental cursor_path field is present in the rows and looks like a sortable timestamp/id.

A live failure (unreachable host, auth rejected) comes back as error with empty rows — fix credentials or the URL and retry. Iterate Steps 2–4 until the sample looks right.

Step 5 — Create the source

Call data-warehouse-source-setup with { source_type: "Custom", payload: { manifest_json, auth_token }, prefix: "<short_name>" } (the auth_token key varies by auth type, as in Step 3). It enables every resource in the manifest with sensible sync defaults (incremental where the manifest declares a cursor, else full refresh) and creates the source. If the user only wants a subset of resources, use external-data-sources-create with a schemas array instead (see setting-up-a-data-warehouse-source for the schemas shape). Pick a short lowercase prefix — tables become {prefix}_{resource_name} in HogQL.

After creation, call external-data-schemas-list to show the user the initial sync status, and tell them how to query: SELECT * FROM {prefix}_{resource_name} LIMIT 10.

Important notes

• Always preview before creating. db-schema proves the manifest parses and the credential works; preview proves the field mappings (data_selector / primary_key / cursor_path) against real rows. Skipping preview is the most common way to create a source that syncs zero or malformed rows.
• Secrets only in auth_*. Never inline a token/key/password in manifest_json — it's rejected, and the manifest is non-secret (it round-trips to the client).
• One level of fan-out. A child resource may depend on a top-level parent; a parent can't itself be a child.
• GET and POST only. The engine reads upstream data; PUT/PATCH/DELETE are rejected so a manifest can't mutate the source API.
• Pick the cursor carefully. Prefer an updated_at-style field over created_at (it catches edits), and set cursor_type when the cursor isn't a datetime (e.g. an integer id) so it's compared with the right type.
• OAuth2 secrets are adopted into a server-managed credential store on the first db-schema / preview / create call, and any rotated single-use refresh token is persisted server-side — so keep the entire client.auth block identical across those calls within one setup, and re-submit the same secrets each time. Changing any auth-block field mid-setup discards the stored rotation, and providers that rotate single-use refresh tokens will then reject the next mint until the user fetches a fresh token. Never set auth_oauth2_integration_id yourself (it is server-owned); to reconnect a source whose token broke, update it with re-entered auth_oauth2_client_secret / auth_oauth2_refresh_token. See the OAuth2 section of the manifest reference for the auth block fields.