Postio

Postio is a UK data validation API covering address, email and phone.

Address search runs on the full Royal Mail Postcode Address File — around 30 million delivery points including organisations, sub-premises and multiple-residency properties, synced nightly. A customer types a few characters, picks their address from real suggestions, and the form fills with a postally correct result. Responses carry the structured fields you need, including address lines, post town, postcode components, building names, thoroughfare, a unique delivery point reference, and latitude, longitude, eastings and northings.

Email validation checks syntax, resolves mail exchange records and probes the mailbox. Phone validation checks syntax and queries the carrier network, returning number type, carrier and porting status.

Pricing is pay as you go. Searching is free, however many keystrokes it takes — you are charged 2.2p only when you retrieve an address, and nothing when a search finds no match. Email and phone validation are 1p each. No monthly fee, no minimum spend, no contract, and the same rate at every volume.

You can use it through a drop-in JavaScript widget of roughly 4KB, a WordPress plugin covering WooCommerce and the major form builders, official SDKs for JavaScript and Node, Python, PHP, Ruby, Go and .NET, or the REST API directly with a published OpenAPI specification. There is also a Model Context Protocol server for AI coding tools.

Postio is a trading name of Onno Group Limited, registered in England and Wales. New accounts get 100 free lookups without a card.