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Postio — UK Address, Postcode, Email & Phone Validation

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Validate UK addresses, postcodes, emails and phone numbers — Royal Mail PAF, live SMTP and HLR.

Source code Website Documentation

Install

Add this to your client's MCP configuration (Claude Desktop: claude_desktop_config.json; Cursor: .cursor/mcp.json; VS Code and others use the same "mcpServers" shape).

NPM package @postio/mcp
Claude Code 
claude mcp add postio-uk-address-postcode-email-phone-v -e 'POSTIO_API_KEY=<your postio_api_key>' -e 'POSTIO_BASE_URL=<POSTIO_BASE_URL>' -- npx -y @postio/mcp@0.1.5
JSON configuration (Claude Desktop, Cursor, VS Code) 
{
    "mcpServers": {
        "postio-uk-address-postcode-email-phone-v": {
            "command": "npx",
            "args": [
                "-y",
                "@postio/mcp@0.1.5"
            ],
            "env": {
                "POSTIO_API_KEY": "<your postio_api_key>",
                "POSTIO_BASE_URL": "<POSTIO_BASE_URL>"
            }
        }
    }
}

Environment variables

  • POSTIO_API_KEY required secret Postio API key (pk_…). Free key, first 100 lookups on us, no card: https://postio.co.uk/signup
  • POSTIO_BASE_URL Override the API base URL. Defaults to https://api.postio.co.uk/v1 (include /v1). Only needed for staging.

Documentation

From the project's README on GitHub, refreshed weekly. Links open on GitHub.

Contents
  1. postio-integrations
  2. Packages
  3. Layout
  4. Building
  5. Contributing
  6. License

postio-integrations

Postio is the UK validation API for addresses, emails and phone numbers. This repo holds the JS-family npm packages, the AI / agent surface, and the cdn.postio.co.uk Worker that powers Postio's browser drop-in.

First time? Sign up free — first 100 lookups on us, no card needed.

The Postio API + OpenAPI spec live in postio-uk/postio-api. The spec is also published as @postio/openapi.

Packages

PackageWhat it is
@postio/api-typesTypeScript types generated from the OpenAPI spec.
@postio/coreRuntime-agnostic typed client (browser / Node / Workers / Bun / Deno).
@postio/nodeNode SDK on top of core — retries with exponential backoff, structured logger hook.
@postio/postman-collectionPostman v2.1 collection for every endpoint.
@postio/address-finderBrowser address autocomplete — ARIA combobox, themable, framework-agnostic source.
@postio/address-finder-bundledThe same component prebuilt for <script> tag use.
@postio/reactReact hooks + <AddressFinder /> component, TanStack Query under the hood.
@postio/mcpModel Context Protocol server — npx -y @postio/mcp for Claude Desktop / Cursor / Windsurf / Zed.

Layout

packages/         pnpm workspace; one publishable npm package per subdir
ai/               AI / agent surface (Claude Skill, GPT Action, recommendation prompts)
cdn-worker/       Cloudflare Worker that serves the address-finder bundles
.github/workflows/  CI for publishing + deploying

Building

cd packages
pnpm install
pnpm -r run build

Each package builds independently (pnpm -F @postio/<name> run build). The address-finder bundle has a topological-build quirk — use the ... suffix so its workspace dep builds first:

pnpm -F "@postio/address-finder-bundled..." run build

Contributing

PRs welcome. Conventions:

  • Node 22+, pnpm 10+, ESM only, MIT-licensed.
  • stage is the working branch; master deploys / publishes via CI.
  • One package change per PR where possible.
  • Versions on each package are independent SemVer; bump the version in package.json when you intend a release.

The full integration index — including the server SDKs in their own repos and the WordPress plugin — lives at postio.co.uk/integrations.

License

MIT.

Frequently asked questions

What is Postio — UK Address, Postcode, Email & Phone Validation?

Validate UK addresses, postcodes, emails and phone numbers — Royal Mail PAF, live SMTP and HLR.

How do I install Postio — UK Address, Postcode, Email & Phone Validation?

It runs on your machine. In Claude Code: claude mcp add postio-uk-address-postcode-email-phone-v -e 'POSTIO_API_KEY=<your postio_api_key>' -e 'POSTIO_BASE_URL=<POSTIO_BASE_URL>' -- npx -y @postio/mcp@0.1.5. For other clients, paste the JSON configuration from this page into their MCP settings.

Does Postio — UK Address, Postcode, Email & Phone Validation need an API key?

Yes. It expects POSTIO_API_KEY, which you set in its configuration.

Is Postio — UK Address, Postcode, Email & Phone Validation open source?

Yes. Its code is on GitHub under the MIT license.

Who maintains Postio — UK Address, Postcode, Email & Phone Validation?

It is published by postio-uk. AI.tn lists it but does not maintain or endorse it.

From the official MCP Registry. Listing is not an endorsement: review a server's code and permissions before giving it access to your data.