Subscribe to Companies House real-time filing events using the Streaming API

Steps

1. Register for a Companies House API key at developer.company-information.service.gov.uk — a streaming key is separate from the standard public data API key and must be requested specifically
2. Open a long-running HTTP GET connection to the streaming endpoint for filing history (the base URL and path are documented at developer-specs.company-information.service.gov.uk/streaming-api); pass your streaming API key via HTTP Basic Auth with the key as the username and an empty password
3. Record the timepoint value from each received event envelope; on reconnect, pass the last seen timepoint as a query parameter so the stream resumes without gaps rather than replaying from the beginning
4. Parse the server-sent event stream; each JSON event envelope contains resource_kind, resource_id, resource_uri, published_at, timepoint, and a data object with the filing metadata (form type, description, action date)
5. To fetch the full filing document list for a company triggered by a streaming event, call the Public Data API at GET https://api.company-information.service.gov.uk/company/{company_number}/filing-history using the standard REST API key
6. Handle disconnections gracefully — the streaming connection drops periodically; reconnect immediately with the last stored timepoint to avoid missing events