Agent Use Interface (AUI)

A lightweight, XML-based schema that enables LLM agents to discover and construct URL-parameter-driven tasks on behalf of users.

Overview

AUI describes actions that are performed by composing query parameters onto a base URL — things like searches, filters, form pre-fills, share intents, and configuration links. It is intentionally narrow in scope:

• It is not a general-purpose API description format (use OpenAPI for that).
• It is not a path-templating system (use RFC 6570 for that).
• It is not a bidirectional agent protocol (use MCP for that).

AUI is a lightweight XML catalog, served at /agents/aui.xml, that both agents and humans can read. Large sites can split full task definitions into linked detail files.

Quick Links

Resource	URL
Specification	agentuseinterface.org/spec/0.1
XML Schema (XSD)	agentuseinterface.org/schema/0.1/aui.xsd
Schematron	agentuseinterface.org/schema/0.1/aui.sch
Example	example/aui.xml
Website	agentuseinterface.org

How It Works

1. Publish — A site serves aui.xml at /agents/aui.xml describing its URL-driven tasks.
2. Discover — An LLM agent finds the file via llms.txt or the conventional path.
3. Parse — The agent reads the XML to understand available tasks, parameters, and constraints.
4. Construct — Based on user intent, the agent builds a URL with the right query parameters.
5. Present — The user receives a link that opens the right experience — on web or in a native app.

Example

<aui xmlns="https://agentuseinterface.org/schema/0.1" version="0.1">
  <name>Example Shop</name>
  <origin>https://shop.example.com</origin>
  <description>An online electronics store.</description>
  <tasks>
    <task id="product-search">
      <name>Search Products</name>
      <description>Search the product catalog.</description>
      <base-path>/search</base-path>
      <parameters>
        <param name="q" type="string" required="true">
          <description>The search query.</description>
        </param>
        <param name="category" type="enum">
          <description>Filter by category.</description>
          <options>
            <option value="electronics">Phones, tablets, laptops.</option>
            <option value="audio">Headphones, speakers.</option>
          </options>
        </param>
      </parameters>
    </task>
  </tasks>
</aui>

User says: "Find me noise cancelling headphones under $200"

Agent constructs: https://shop.example.com/search?q=noise+cancelling+headphones&category=audio&price_max=200

In the Wild

Apps and websites using AUI today:

App	Platform	AUI File
Habit Tiles	iOS	aui.xml

Validation

Run the same checks used in CI:

./scripts/validate.sh

This validates:

• XSD structure (schema/0.1/aui.xsd)
• Schematron semantic rules (schema/0.1/aui.sch)
• Catalog/detail id matching for reference tasks in example/aui.xml

Repo Structure

agent-use-interface/
├── agent-use-interface-spec.md   # The specification (source of truth)
├── schema/0.1/aui.xsd            # Normative XML Schema Definition
├── schema/0.1/aui.sch            # Semantic validation rules (Schematron)
├── example/
│   ├── aui.xml                    # Full working example
│   ├── aui.css                    # Reference stylesheet for browser rendering
│   └── aui-browser-preview.html   # HTML preview of styled XML
├── scripts/                       # Validation scripts used by CI
├── public/                        # Website (agentuseinterface.org)
│   ├── index.html
│   ├── style.css
│   ├── spec/0.1/index.html
│   ├── schema/0.1/aui.xsd
│   ├── schema/0.1/aui.sch
│   └── example/
└── firebase.json                  # Hosting config

Contributing

AUI is in early draft. Feedback is welcome — open an issue to share thoughts, suggest changes, or report problems.

License

• Specification prose (agent-use-interface-spec.md): CC BY 4.0
• Code, schema, and website: Apache License 2.0