The Rise of the User Agent Interface (UAI)

Building websites for both humans and their AI agents

For more than 30 years, the web has been built around one assumption: a human will open a browser, look at a page, and decide what to do next.

That’s still true,  but it’s no longer the whole story. Increasingly, people are delegating their online tasks to AI agents: AI assistants, search overviews, large language models, browser extensions, and other tools that act on their behalf. These agents don’t “see” a site the way we do. They scan, parse, and interpret — and then act, often without the human ever visiting the site themselves.

User Agent Interface (UAI) work is about designing for both audiences at once. It’s the sweet spot where:

• A human gets a fast, elegant, and accessible experience;
• An agent gets the clean, structured, and standards-compliant data it needs to act accurately and efficiently

And here’s the kicker: when you design well for agents, you often make the site better for humans too: faster load times, clearer navigation, and content that’s accessible and easier to understand.

At Plank, our work already bridges design, development, and content strategy. UAI thinking just turns that bridge into a two-lane highway: one lane for people, the other for their digital helpers.

The big question: How do we build sites today that can support humans and their agents equally well?

1. Build for Speed

When a human asks an agent to “find the best option,” speed matters.

Agents will prefer sources that deliver answers faster than the competition. That means:

• Lightweight/unbloated markup
• Smart caching and CDNs
• Minimal blocking scripts and thoughtful page load sequences
• Performance budgets are a part of every project

Like a store with no checkout line, fast sites win repeat visits from both humans and agents.

2. Build for Ease of Scan

For agents, “scan-ability” is accessibility in another form.

• Semantic HTML isn’t just for screen readers; it’s for machines parsing intent
• Clear heading structures and ARIA roles give agents faster context
• Logical reading order ensures agents extract key points without misinterpretation

Clear headings and structure are like perfect signage: agents find what they need instantly.

3. Build on Standards

Technology will shift, but open standards stick around.

• HTML5 elements, microformats, and schema.org metadata
• Avoiding proprietary lock-in for critical data
• Designing API responses that conform to REST or GraphQL best practices

Open standards today are your best chance at future-proofing for whatever UAI protocols come next.

4. Build With Agents

Don’t just design for them, test with them.

• Create a user persona for an agent—even a simple one will keep you thinking about its goals, limitations, and context as you map user journeys and plan features
• Use your own tools (LLMs, crawlers, accessibility scanners) during dev to see how machines interpret your work
• Identify how your markup reads when stripped of styles and scripts
• Start experimenting with Model Context Protocols (MCP) to let agents take structured actions

A good example would be an e-commerce store that enables agents to be used as a shopping assistant by adding products to a cart, then providing a link for the user to finish checkout.

5. Provide Tools

Agents will need structured access points to act, not just read.

• Public APIs and MCP services
• Well-documented endpoints for common tasks (search, booking, content retrieval)
• Authentication that supports both people and agents

APIs and MCP services are like giving agents a front door instead of making them sneak in.

Where This Leads

A “user-friendly” site in 2030 will be one where:

• A person can navigate beautifully-designed pages;
• An agent can independently act, fetch, and interact without scraping hacks;
• Both experiences are accurate, efficient, and mutually reinforcing.

That’s the User Agent Interface mindset: not replacing humans, but designing equally for their chosen representatives, and continuing to create a web for all.

What excites us most at Plank is how accessibility naturally wins in this scenario. We’ve spent years making it a priority in all our work, and this shift only adds more value to that effort.

There’s no doubt this is the future, and building with UAI principles gives web developers a clear, practical game plan to keep doing what we love — while embracing the changes ahead.

Design your site for the AI-powered web

From semantic markup to schema design, we can optimize your site to help UAI agents surface it above the competition. Get in touch to find out more.

Credit to Josh Beckman for his post:
UI VS. API. VS. UAI
https://www.joshbeckman.org/blog/practicing/ui-vs-api-vs-uai