Agent-First is the new Mobile-First: Designing UIs for 2025's On-Site Agents

Remember when "mobile-first" was a radical idea? When designers scoffed at the notion of prioritizing tiny screens over desktop monitors? Fast forward to today: mobile accounts for 60% of web traffic, and mobile-first isn't just best practice — it's table stakes.

We're at that same inflection point again. But this time, the new "device" isn't a smartphone. It's an AI agent.

Why Now? The Agentic Wave is Here

In Q4 2024 and Q1 2025, we witnessed an unprecedented shift. OpenAI shipped Computer Use, Microsoft integrated Copilot Vision into Edge, and Apple's Apple Intelligencebrought on-device agents to Safari. These aren't research previews — they're production features rolling out to hundreds of millions of users.

The implication? Your website is about to receive traffic from non-human visitors that expect to complete tasks, not just browse.

What Breaks with Pixel-Only Agents

Most early agentic systems rely on vision models and OCR to understand web pages. They take screenshots, analyze pixels, and attempt to locate clickable elements.

This approach has fundamental limitations:

Agent-First Design Principles

The solution isn't to abandon visual design or user experience. It's to layer semantic meaning on top of your existing UI so agents can understand intent without relying solely on pixels.

1. Semantic Hooks Everywhere

Add data-* attributes to describe what elements do, not just what they look like.

<!-- ❌ Bad: No semantic information -->
<button class="btn-primary">Update</button>
<button class="btn-primary">Update</button>

<!-- ✅ Good: Clear semantic hooks -->
<button
  data-action="update-shipping-address"
  data-entity="shipping-address"
  aria-label="Update shipping address">
  Update
</button>
<button
  data-action="update-billing-address"
  data-entity="billing-address"
  aria-label="Update billing address">
  Update
</button>

2. Stable Selectors

Avoid auto-generated class names that change on every build. Use consistent, human-readable identifiers.

<!-- ❌ Bad: Unstable selectors -->
<div class="card-8392">
  <button class="btn-a6f2">Submit</button>
</div>

<!-- ✅ Good: Stable, semantic selectors -->
<div data-component="payment-form" class="payment-card">
  <button
    data-action="submit-payment"
    data-test-id="payment-submit"
    class="submit-button">
    Submit Payment
  </button>
</div>

3. Explicit Intent Declarations

Don't make agents guess. Tell them exactly what will happen when they interact with an element.

4. Guardrails for High-Stakes Actions

Not all actions should be agent-accessible. Use data-agent-policy to control what agents can do.

Handoff Protocol: User Agent ↔ Site Agent

Here's where it gets really interesting. Instead of the user's agent (like OpenAI's or Microsoft's) fumbling through your site with screenshots, what if your site had its own agent that could handle the task natively?

This is the handoff protocol — and it's what Warpway enables.

// Handoff protocol example
interface AgentHandoff {
  requestingAgent: {
    id: string;
    capabilities: string[];
  };
  task: {
    intent: string;
    targetAction: string;
    context: Record<string, any>;
  };
  siteAgent: {
    canHandle: boolean;
    estimatedSteps: number;
    requiresAuth: boolean;
  };
  proofOfAction?: {
    timestamp: string;
    actionsTaken: string[];
    outcome: 'success' | 'failure' | 'partial';
    verification: string; // cryptographic proof
  };
}

Accessibility ≈ Agentability

If you've built accessible websites, you're already halfway to agent-first design. ARIA roles, semantic HTML, and keyboard navigation all help agents understand your UI.

But agent-first goes further. While accessibility ensures humans can use assistive technology, agent-first ensures AI systems can autonomously complete tasks on behalf of users.

Launch Checklist

Download the Schema

We've created a JSON schema for data-action contracts that you can use to validate your markup.

The Bottom Line

Agent-first design isn't about replacing humans. It's about meeting users where they are — and increasingly, that's through AI agents acting on their behalf.

Sites that embrace this shift will see:

Sites that ignore it? They'll be the equivalent of the mobile-hostile Flash sites of 2010 — technically functional, but frustrating and obsolete.