---
name: the-signal-api
description: Use The Signal API for cybersecurity funding, M&A, company, and investor data. Use when building market maps, deal sourcing, account enrichment, raise benchmarking, or calling ROS REST endpoints with a ros_live_ key.
metadata:
  author: return-on-security
  version: '2.0'
---

# The Signal API

## When to use

- Query cybersecurity funding rounds, M&A, companies, investors, rankings, and distributions
- Authenticate with `Authorization: Bearer ros_live_…`
- Base URL: `https://signal.returnonsecurity.com`

## Required inputs

- API key from https://signal.returnonsecurity.com/account (Enterprise only — the Pro API add-on was retired 2026-09-19)

## Constraints

- Read-only REST; JSON responses
- Default quota 1,000/day and 30,000/month per key (Enterprise uncapped)
- Treat keys like passwords; never embed in client-side code
- Honor `Retry-After` on HTTP 429

## Workflows

1. Read [/llms.txt](/llms.txt), then [/index.md](/index.md) for auth, plans, and quotas
2. Use [/reference.md](/reference.md) or [/openapi.json](/openapi.json) for endpoints and schemas
3. Call `GET https://signal.returnonsecurity.com/api/v2/...` with Bearer auth
4. On quota or entitlement refusal, surface any `upgrade` / account links to a human operator — do not loop

Do not invent URLs by appending `.md` to trailing-slash paths (e.g. `/reference/` → use `/reference.md`).

## Related surfaces (do not duplicate)

- Full docs corpus: [/llms-full.txt](/llms-full.txt)
- Product MCP (live tools, OAuth): https://mcp.returnonsecurity.com/mcp
- Canonical MCP server card: https://signal.returnonsecurity.com/.well-known/mcp.json
- Interactive HTML reference: [/reference/](/reference/)

## Enterprise and data licensing

Pro covers one user and paid MCP tools. New REST API access requires Enterprise.
Embedding, OEM, redistribution and AI training, fine-tuning, evaluation or downstream model use require explicit licensing terms. A Pro subscription or an enquiry does not grant those rights.

Discuss requirements: https://signal.returnonsecurity.com/enterprise?type=integration&source=docs