OpenAPI & AI resources Developer site Get an API key Download specSpec

OpenAPI & AI resources

OpenAPI definitions, a Postman collection and llms.txt files for code generators, API clients and AI assistants.

Looking for guides, SDKs and tutorials? They live on the what3words developer site. developer.what3words.com
Download OpenAPI spec Browse endpoints

Files

Machine-readable descriptions of the what3words API, ready to import into your tools or give to an AI assistant.

OpenAPI (YAML)The source definition, for code generators and API clients OpenAPI (JSON)The same definition in JSON Postman collectionImport into Postman and start sending requests llms.txtA curated index of what3words guides for AI assistants llms-full.txtThe complete guide in one file for AI assistants

Building with an AI assistant?

Point your coding agent at llms.txt for a curated index, or llms-full.txt for the complete guide in one file. It can read the OpenAPI definition for exact parameters and responses.

Endpoints

Every operation in the definition, with parameters, response fields and examples.

Base URLhttps://api.what3words.com/v3

Authentication

Every request needs an API key. Send it in either of these ways.

MethodExample
HeaderX-Api-Key: YOUR_API_KEY
Query parameter?key=YOUR_API_KEY

Create and manage keys in your what3words account, or compare API plans.

Errors

Errors return an HTTP status and a JSON body with a stable code and a readable message. Branch on code, and handle codes you do not recognise.

StatusMeaning
400A parameter is missing or invalid
401The API key is missing, invalid or lacks permission
402The feature is not on your plan, or your quota is used up