---
title: "What each signal checks"
method: GET
path: "/signals/definitions"
tags: ["Signals"]
---

# What each signal checks

`GET /signals/definitions`

## Request

- Base URL: `https://api.companystack.co.uk`
- URL: `https://api.companystack.co.uk/signals/definitions`
- Auth: one of:
  - HTTP bearer
  - API key in header `X-Api-Key`

Every signal's logic, sources with their licences and attribution, known false positives, and the SIC-to-register map. The same data is public (no key) at /public/signals/definitions.

## Response `200`

Definitions

## Other responses

- `401`: API key missing, malformed or revoked
- `403`: The key's plan does not include this endpoint (`code: plan_upgrade_required`, with `upgrade_url`), the key may not call it, or the key is beyond the plan's key limit after a downgrade (`code: key_limit_exceeded`: the newest keys are paused until keys are deleted or the plan upgraded)
- `429`: Per-minute or per-day limit reached (`code: rate_limited`, `window: minute|day`). Wait `Retry-After` seconds; when both windows are full the day is reported. A refused request does not count against either limit. A bulk lookup (`POST /company/bulk`) counts each company number in it as one request, so one that is more than you have left is refused whole, and the body adds `requested` and `fits`.

---

[API](https://skmtc.dev/companystack/apis/companystack-api.md) · [All operations](https://skmtc.dev/companystack/apis/companystack-api/llms.txt) · [OpenAPI document](https://skmtc.dev/companystack/apis/companystack-api/revisions/8f3234237d2d?raw)