AX: A Design Discipline for the AI Agent Era

If you've built an MCP server, exposed tools for an AI agent, or crafted tool descriptions so the AI would call the right endpoint, you've been practicing Agent Experience — AX, a term Mathias Biilmann coined in early 2025. The current AX conversation tells you it matters. But knowing it matters and knowing how to evaluate it are different things. UX became a discipline when practitioners connected it to User-Centered Design and gave it testable principles and evaluation methods. AX needs the same grounding. UX, DX, CX... AX Every era of software recognizes that a particular consumer deserves intentional design. UX (end users), DX (developers), CX (customers) — each started informally, then someone named the discipline, principles emerged, and quality went up. AX — Agent Experience — follows the same arc. The new consumer is an AI agent: an LLM that reads your tool definitions, decides which to call, and orchestrates workflows. Biilmann and Netlify named it and showed why it matters. W