Postio.co.uk
UK address, email, and phone validation APIs. Sub-50ms p95. Pay-per-request, no tiers, no contracts.
A startup from the United Kingdom.
UK address, email, and phone validation APIs. Sub-50ms p95. Pay-per-request, no tiers, no contracts.
A startup from the United Kingdom.
This page is designed to help you find out whether Postio.co.uk is good and if it is the right choice for you.
Postio is a UK validation API for developers. Address search and postcode lookup run on Royal Mail PAF data under a direct licence; email validation covers syntax, typo, MX and deliverability; phone validation does a live HLR carrier lookup. All endpoints are GET and return the same JSON envelope. 2.2p per address, 1p per email or phone — searching is free, you're only charged on a result. 100 free lookups, no card.
Listed in
Address search
UK address typeahead over Royal Mail PAF data, held under a direct licence
Postcode lookup
Every PAF delivery point at a given postcode
UDPRN lookup
Full address record by Royal Mail Unique Delivery Point Reference Number
Email validation
Syntax, typo correction, MX, SMTP check and deliverability classification
Phone validation
Parse and validate, plus live HLR lookup for carrier, ported status and reachability
Pricing model
Pay per request — 2.2p per address, 1p per email, 1p per phone. No tiers, no contracts
Free tier
100 lookups, no card required
API design
All endpoints are GET and return the same JSON envelope. Public OpenAPI spec, CORS enabled
SDKs and integrations
Official SDKs for JavaScript/Node, Python, Go, PHP, Ruby and .NET. Drop-in browser widget (~4 KB gzipped), MCP server for AI agentsOfficial SDKs for JavaScript/Node, Python, Go, PHP, Ruby and .NET. Drop-in browser widget (~4 KB gzipped), MCP server for AI agents
Postio charges only when a lookup returns a result — searching is free. Address, email and phone validation sit behind one API with a single JSON response envelope, so you integrate once rather than stitching three vendors together. Address data comes from Royal Mail's Postcode Address File under a direct licence, not scraped or resold sources. There are no tiers, contracts or minimum spend, and the first 100 lookups need no card.
A REST API served from edge locations, with official SDKs for JavaScript/Node, Python, Go, PHP, Ruby and .NET, all open source on GitHub. The API is documented by a public OpenAPI specification.
Pricing is published and pay-as-you-go: 2.2p per address, 1p per email, 1p per phone, billed only on a result. No sales call, no annual contract, no minimum commitment. You can be live in a few minutes with 100 free lookups and no card, and the same API covers all three validation types. For UK addresses specifically, the data is licensed directly from Royal Mail rather than obtained second-hand — which matters after the 2025 High Court ruling on database rights in this market.
Developers and technical teams building UK-facing forms — ecommerce checkouts, signup flows, CRM and logistics systems. Typically small to mid-sized product teams, agencies building for UK clients, and software vendors embedding address lookup in their own product. It suits anyone who wants a UK-accurate API without an enterprise procurement process.
Postio is a trading name of Onno Group Limited, registered in England & Wales (company no. 08622799). It was built to make Royal Mail PAF-accurate UK validation available on straightforward pay-as-you-go pricing, rather than the contracts and minimum commitments that have been standard in this market. Address, email and phone validation were brought together behind one consistent API so a team can solve all three at once.
Serving a huge range of customers across the world looking for a blazing fast UK Address AIP product. From bootsrapped entrepreuners to FTSE 250 companies. We serve them all.
We have collected here some useful links to help you find out if Postio.co.uk is good.
Check the traffic stats of Postio.co.uk on SimilarWeb. The key metrics to look for are: monthly visits, average visit duration, pages per visit, and traffic by country. Moreoever, check the traffic sources. For example "Direct" traffic is a good sign.
Check the "Domain Rating" of Postio.co.uk on Ahrefs. The domain rating is a measure of the strength of a website's backlink profile on a scale from 0 to 100. It shows the strength of Postio.co.uk's backlink profile compared to the other websites. In most cases a domain rating of 60+ is considered good and 70+ is considered very good.
Check the "Domain Authority" of Postio.co.uk on MOZ. A website's domain authority (DA) is a search engine ranking score that predicts how well a website will rank on search engine result pages (SERPs). It is based on a 100-point logarithmic scale, with higher scores corresponding to a greater likelihood of ranking. This is another useful metric to check if a website is good.
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