# The Signal API

> Programmatic REST access to the cybersecurity market dataset behind The Signal by Return on
> Security — funding rounds, M&A, companies, investors, and the analytics built on them.

The API is read-only, returns JSON, and is authenticated with a Bearer key (`Authorization: Bearer
ros_live_…`). Base URL: https://signal.returnonsecurity.com. Mint a key at
https://signal.returnonsecurity.com/account (Enterprise only — the Pro add-on was retired 2026-09-19).
Pro is priced per seat for one user; Enterprise provides tailored team seats for organisations and
teams, with custom pricing.

Markdown versions of the guide and reference live at [/index.md](/index.md) and
[/reference.md](/reference.md) (also via `Accept: text/markdown`). Full corpus:
[/llms-full.txt](/llms-full.txt). Agent skill: [/skill.md](/skill.md).

## Docs

- [Overview & guides](https://docs.returnonsecurity.com/index.md): what you can build, quickstart,
  authentication, rate limits & quotas, and errors.
- [API Reference](https://docs.returnonsecurity.com/reference.md): endpoint list generated from the
  public OpenAPI spec, plus link to the interactive Scalar UI.
- [OpenAPI spec](https://docs.returnonsecurity.com/openapi.json): the machine-readable contract
  (OpenAPI 3.1).
- [Agent skill](https://docs.returnonsecurity.com/skill.md): when to use the API, required inputs,
  and constraints.

## Product MCP (live — not hosted on this docs site)

- [MCP endpoint](https://mcp.returnonsecurity.com/mcp): Model Context Protocol tools over the same
  dataset (OAuth). Docs discovery at [/.well-known/mcp.json](/.well-known/mcp.json) only *points*
  here — it does not duplicate the tool server.
- [Canonical MCP server card](https://signal.returnonsecurity.com/.well-known/mcp.json): full tool
  catalog and pricing notes (maintained with the product).

## What you can build

- Market mapping & deal sourcing — landscape views of funded cybersecurity companies with round
  sizes, investors, and timing.
- M&A and consolidation tracking — acquisitions, acquirers, and buyer types.
- GTM targeting & account enrichment — surface security companies by stage/category after a raise.
- Raise benchmarking — compare a round against stage percentiles by category.

## Limits

- Enterprise keys are uncapped. 1,000 requests/day and 30,000 requests/month
  per key apply to the closed, grandfathered add-on cohort. Responses carry `X-Quota-*`,
  `X-Data-Freshness`, and `X-Request-Id` headers; a `429` includes `Retry-After`.