> For the complete documentation index, see [llms.txt](https://docs.os.uk/os-apis/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.os.uk/os-apis/accessing-os-apis/os-features-api/technical-specification.md).

# Technical specification

The technical specification explains the content of OS Features API and the methods you can use to call it.

The OS Features API lets you call and interact with OS data, including the highly detailed OS MasterMap Topography Layer. It does this by exposing the data through an Open Geospatial Consortium Web Feature Service (OGC WFS).

{% hint style="info" %}
If you are not familiar with OS Features API, please read the [Overview documentation ](/os-apis/accessing-os-apis/os-features-api.md)before proceeding.
{% endhint %}

## Core concepts

This specification does not cover core concepts that apply to all Ordnance Survey APIs.

Please read the following pages to learn more about OS API core concepts:

* [Authentication](/os-apis/core-concepts/authentication.md)
* [Error codes](/os-apis/core-concepts/error-codes.md)
* [Rate-limiting policy](/os-apis/core-concepts/rate-limiting-policy.md)

## API reference

The OS Features API exposes data through an Open Geospatial Consortium Web Feature Service (OGC WFS).

The OGC WFS accepts three types of requests:

<table data-view="cards"><thead><tr><th></th><th></th><th data-hidden data-card-target data-type="content-ref"></th></tr></thead><tbody><tr><td><strong>getCapabilities</strong></td><td>Returns a metadata describing the WFS service.</td><td><a href="/os-apis/accessing-os-apis/os-features-api/technical-specification/getcapabilities.md">getCapabilities</a></td></tr><tr><td><strong>describeFeatureType</strong></td><td>Returns a description of the attributes for each feature type.</td><td><a href="/os-apis/accessing-os-apis/os-features-api/technical-specification/describefeaturetype.md">describeFeatureType</a></td></tr><tr><td><strong>getFeature</strong></td><td>Returns a selection of specific features, including  attribute values and geometry.</td><td><a href="/os-apis/accessing-os-apis/os-features-api/technical-specification/getfeature.md">getFeature</a></td></tr></tbody></table>


---

# Agent Instructions
This documentation is published with GitBook. GitBook is the documentation platform designed so that both humans and AI agents can read, navigate, and reason over technical content effectively. Learn more at gitbook.com.

## Querying This Documentation
If you need additional information that is not directly available in this page, you can query the documentation by asking a question.

Perform an HTTP GET request on the following URL with the `ask` and `goal` query parameters:

```
GET https://docs.os.uk/os-apis/accessing-os-apis/os-features-api/technical-specification.md?ask=<question>&goal=<user_goal>
```

`ask` is the immediate question: it should be specific, self-contained, and written in natural language.
`goal` is what the user is ultimately trying to achieve, the reason they need the answer. Sharing it helps GitBook give you a better, more relevant answer. A goal is most helpful when it describes the outcome the user wants rather than restating the question. For example, with `ask=how do I create an API token`, a goal like `automate deployments from our CI pipeline` lets GitBook tailor the answer to that use case.

The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.