What is RPML?

RPML (Rapid Prototype Markup Language) is a static UI specification language. A .rpml file is one screen or functional region: the layout, every interaction state, permission variant, and loading / empty / error / validation branch, written as markup a person can read and a coding agent can implement.

It is not HTML you ship. It is not a clickable prototype. Time is replaced with space — states sit next to each other in one annotated layout, so a reviewer does not have to ask "but what happens when…".

OriginAI stores product specs as RPML. You edit them in the workbench, publish a release, and Claude Code, Cursor, or Codex reads that frozen snapshot through the originai CLI or MCP.

Why a language instead of a screenshot or a PRD

Screenshots miss states. A PRD goes stale and skips the empty table, the admin-only button, and the confirm dialog. Markdown task lists (the usual spec-driven-development kit) describe what to build next, not what the product looks like when each rule fires.

RPML is for that product contract:

• One .rpml file per screen or region, rooted at <page>.
• A single <view> snapshot built from RPML primitives (button, table, navigator, …) — not raw div / input.
• Numbered pins (data-pin) with matching <annotation> blocks for the rules that belong to each region.
• <enum> / <enum-item> for conditional branches instead of burying them in prose.

The runtime that paints those files in a browser is @21stware/rpui. OriginAI's workbench uses the same language. Locally you can also npx @21stware/rpui serve . on a folder of .rpml files.

How OriginAI uses RPML

1. Author — generate or write .rpml in the workbench (or have a coding agent write it via originai write-document before the first release).
2. Validate — npx originai validate --content "…" checks the file locally, no token required.
3. Publish — a release freezes the tree. Agents implement that version, not the live draft.
4. After publish — further agent writes become change requests you apply or dismiss.

See Files and README for how a multi-page product is split (README first, then one file per route).

RPML is not

• Not a replacement for Claude Code, Cursor, or Codex. Those tools write the product. RPML tells them what "done" looks like on each screen.
• Not GitHub Spec Kit. Spec Kit is a markdown specify → plan → tasks → implement workflow that lives in your repo. RPML is the visual product spec those tasks should implement. See OriginAI vs Spec Kit.
• Not Proto Markdown or a generic "rapid prototyping markup". RPML is the language OriginAI and @21stware/rpui speak.

Related

• What is OriginAI?
• OriginAI vs GitHub Spec Kit
• Files and README
• OriginAI CLI (validate, write-document, get-diff)