# Peer39

> Peer39 is a contextual advertising and intelligence company providing pre-bid controls and post-buy analytics built on verified contextual data for programmatic media buyers — contextual targeting, brand safety and suitability, and contextual analytics across web, mobile, CTV and video. Peer39 operates a real REST API, the **Peer39 External API** at `https://app.peer39.com/api/external`, for managing Custom Categories (contextual targeting and brand-safety lists) and syncing them to connected DSPs. It is credential-gated and undocumented in public: there is no developer portal, no API reference page, and no OpenAPI specification. Credentials are provisioned by a Peer39 account or integration manager who grants the "External API" and "RTB Buyer" roles.

## API surface

- Base URL: `https://app.peer39.com`, path prefix `/api/external`
- Auth: POST `/api/external/login` with username + password returns a `sessionId`, carried as `Authorization: Bearer <sessionId>`. Not OAuth. Not an API key.
- Errors: HTTP 200 with a `{value, code, description, message}` envelope; a **non-zero `code` is an error even on a 200**. Twenty error codes are known.
- No versioning, no idempotency, no rate-limit headers, no status page, no changelog, no webhooks.
- Every path under `/api/external` returns 401 unauthenticated, including paths that do not exist.

Operations known to exist (from Peer39's own reference client — Peer39 publishes no OpenAPI):

- `POST /api/external/login` — mint a session
- `GET /api/external/customcategories` — list categories (offset paging: `start`, `max` 1-999; server defaults return zero rows, always pass both)
- `GET /api/external/customcategories/{accountCategoryId}` — fetch one category
- `POST /api/external/customcategories` — create a category (requires the `system` header)
- `PUT /api/external/customcategories` — full update
- `PUT /api/external/customcategories/updateBasicDetails` — metadata-only update
- `POST /api/external/customcategories/items` — modify items (**API default is REPLACE, not append**)
- `PUT /api/external/customcategories/delete` — delete (a PUT, not a DELETE)
- `POST /api/external/prediction/urlexamples` — preview URLs matching a keyword set

## Agent surface

- An MCP server for the Peer39 External API exists in **pre-release**: `@peer39/mcp-server`, ten tools, installed via `npx -y github:awhite07/p39-custom-category-mcp#v1.0.9`. A remote OAuth 2.1 connector variant is live at `https://mcp-connector.scatter-brain.ai/mcp` (nine tools).
- Both are first-party-authored ("internal Peer39 project") but published on a personal GitHub account, not on npm, and not hosted on a peer39.com domain. Treat as beta.
- No A2A Agent Card, no `llms.txt`, no `/.well-known/` documents are served on any Peer39 host.

## Company
- [Website](https://www.peer39.com): Peer39 corporate site and solutions overview.
- [Platform](https://www.peer39.com/platform/): Contextual targeting and CTV platform overview.
- [Product](https://www.peer39.com/product): Advanced contextual data for advertisers.
- [Publisher Solutions](https://www.peer39.com/publisher-solutions): Contextual data for publishers.
- [Programmatic Partners](https://www.peer39.com/programmatic-partners): The DSPs and SSPs Peer39 syncs to.
- [Onboarding Guide](https://www.peer39.com/onboarding-guide): Getting started with the platform.
- [Blog](https://www.peer39.com/blog): Contextual advertising, brand safety, and CTV insights.
- [Newsroom](https://www.peer39.com/newsroom): Company announcements.
- [Contact / Support](https://www.peer39.com/contact-us): Sales and support contact for platform access.
- [Sign Up](https://www.peer39.com/signup/): Marketing signup — does not yield API credentials.
- [Platform Login](https://app.peer39.com/login): Authenticated customer application.
- [Crawler Notice](https://www.peer39.com/crawler-notice): Peer39 operates `peer39_crawler/1.0` and honors robots.txt.

## Legal
- [Service Terms](https://www.peer39.com/service-terms)
- [Privacy Policy](https://www.peer39.com/privacy-policy/)
- [Cookie Notice](https://www.peer39.com/cookie-notice)

## Notes
- No public pricing. Enterprise / contact-sales only; `/pricing` returns 404.
- No OpenAPI, AsyncAPI, GraphQL schema, JSON Schema, Postman collection, or published SDK on any registry (npm, PyPI, RubyGems all miss).
- API documentation is distributed as PDFs by account managers rather than published on the web — the reference client cites "Peer39 PDF" as the source of its language-code rules.