Sell Ltd
Last updated 1 January 1970

UK Company Data API — free-tier developer access

TL;DR
One HTTPS endpoint, one bearer token, Companies House data plus our derived signals (health score, phoenix flags, director network) in JSON. Free tier covers most side-projects; metered from there.
Developer preview600 req/hr · 5,000/day · bearer auth · JSON
curl -H "Authorization: Bearer $SELLLTD_TOKEN" \
  "https://sellltd.co.uk/api/v1/company/00445790"
Request a tokenTry the UI first

Why we're building this

A lot of what people pay Endole, CompanyCheck and DueDil for is API access — the ability to power an internal dashboard, a supplier onboarding form or a niche vertical product with UK company data. Those APIs cost £4k–£40k a year with contracts and minimums that don't fit a side project or a light commercial tool. Companies House's own API is free and excellent, but you still have to build the join layer on top — health scoring, phoenix detection, director cross-appointment analysis. That's what our API bundles.

What you get

  • /company/{number} — full profile including derived signals (health score, phoenix flag, next filing due, live charge count).
  • /company/{number}/officers — every director and officer with role, appointment/resignation dates and occupation.
  • /company/{number}/psc — beneficial owners with RLE chain walking.
  • /officers/{id}/appointments — the full director network view for one officer.
  • /search/companies?q=… — name and number search.
  • /search/officers?q=… — director name search.

Rate limits and fair use

The free tier is 600 requests/hour and 5,000/day. That's plenty for personal dashboards and light commercial tools. If your legitimate use trips the limit, contact us — we lift quotas for good faith users while paid tiers spin up. Enterprise volumes (>100k/day) are on a metered plan with SLA and webhook access.

Data lineage

  • Statutory core — Companies House Public Data API. Live, Crown Copyright, freely redistributable under OGL.
  • Insolvency events — The Gazette public notices feed.
  • PSC register — Companies House PSC endpoint, cached at 24h.
  • Derived signals — Sell Ltd's own scoring and pattern-detection layer, based on the transparent rubric in our credit score checker.

Terms in plain English

  • Attribute the derived signals to Sell Ltd if you surface them to users.
  • Don't scrape past the rate limit — we'll ban you and it's tedious for both of us.
  • Don't resell the raw feed as a competing "company data API" — build products, not resellers.
  • Companies House data itself is OGL — attribute it to Companies House.
  • PII (director date of birth) follows Companies House disclosure rules verbatim.

What's coming next

  • Filing-change webhooks — subscribe to any company; get a push when its filing history changes. Currently on the paid tier only.
  • Bulk endpoints — POST an array of company numbers, get back a batch. Under design.
  • TypeScript SDK — will ship when 20+ users say they want it.
  • OpenAPI spec — under review; drop a note on the waitlist to be first when it ships.

How this fits with the rest of the toolset

If you want the same data without code, everything is exposed in the free tools: company checker, credit score, director check, PSC lookup, accounts explorer. The API is the same information, callable from your code.

Request a developer preview token

Free-tier tokens are issued in weekly batches. Email api@sellltd.co.uk with the phrase "developer preview" and a one-line description of what you're building.

Frequently asked questions

Is the API free?

The public research tier is free. Rate-limited to a fair-use cap that comfortably supports personal dashboards, internal tools and low-volume commercial use. Volume beyond that is a metered plan.

How does this differ from Companies House's own API?

Companies House exposes the raw statutory feed. We layer valuation signals, phoenix flags, director cross-appointment scores and cleaned SIC hierarchies on top — the same data you see in the Sell Ltd UI, callable from your code.

What authentication do you use?

Bearer tokens over HTTPS. Get a token from your Sell Ltd account. Rotate any time; scoped by IP is a paid option.

What's the rate limit on the free tier?

600 requests per hour, 5,000 per day. That's enough for most side-projects and light commercial use. Higher volumes are on the metered tier.

Do I need to sign up for a Sell Ltd account?

Yes — the free tier still needs a token so we can rate-limit fairly. Free accounts don't require a payment method.

Can I redistribute the data?

The raw Companies House data is Crown Copyright and freely redistributable under the Open Government Licence. Our derived signals (health score, phoenix flags) are Sell Ltd's — display them, don't resell them. Full terms in the API T&Cs.

Do you have SDKs?

Not yet — the API is small enough that a five-minute fetch integration covers it. If you want a TypeScript SDK, drop a note on the waitlist and we'll add one.

Is there a sandbox?

Yes — every endpoint returns the same fields for the sandbox company '00000000'. Point CI at that to avoid burning production quota.

Do you support webhooks?

On the metered tier. Filing-change webhooks (accounts filed, insolvency notice, director change) push within minutes of the statutory event.

How current is the data?

Companies House feed is live. Derived signals (health score, phoenix flags) recompute nightly and on-demand for cached lookups older than 24h.

Where does the raw data come from?

Companies House Public Data API, the Insolvency Service Gazette feed, the PSC register, HMRC's VAT-registration data (where available), and our own crawl of registered-office public filings.

How do I join the waitlist?

Sign up for a Sell Ltd account and email api@sellltd.co.uk with the phrase 'developer preview' — we'll add you to the next batch of tokens.

Keep exploring

Every UK company research tool we've built, plus honest reviews of the paid alternatives.