opencode/packages/plugin-genui

GenUI plugin

@opencode/plugin-genui lets agents show interactive UI in the OpenCode app. The agent writes a GenUI program in a genui_render call; the timeline draws it with the app's own components while the call streams, and every call is checked so the agent knows whether its UI rendered.

root = Surface([counts, actions])
$approved = 0
counts = Metrics([Metric("Approved", $approved + " of 4")])
actions = Actions([approve, apply])
approve = Button("Approve next", set($approved, $approved + 1), "primary")
apply = Button("Apply", reply("Apply the " + $approved + " approved changes"))

Language

One statement per line, name = Expression, starting with root = Surface(...). Components take positional arguments; values are text, numbers, booleans, null, lists and objects. $name = value declares state that lives in the app; expressions (+ - * / %, comparisons, && || !, ? :) read it, and set, reset, reply and open change it or answer the agent when a button is pressed. There are no loops, functions or host access.

The language is ours and small on purpose: it parses while streaming, checks statically, and has no install scripts, telemetry or third-party prompt text.

Modules

• catalog.ts: every component as the Effect schema of its rendered node. The props struct's key order is the positional order, its types check programs, and the guide prints signatures from it.
• lang.ts and lang/: lexer, parser (incremental while streaming), evaluator, static checks and the type printer. Generic over a catalog.
• guide.ts: the genui skill, generated from the catalog and examples.
• tools.ts: the skill and the genui_render tool, which returns each problem by statement.
• session.ts: offers the tool, and adds a short reminder, only while the session's latest prompt came from the app with generated UI on (metadata.genui = true). The app's Experimental settings turn it off.

./genui, ./lang and ./catalog are browser-safe; session-ui renders with them. . is the server plugin.

Tests

Run bun test and bun typecheck from this package. Every guide example must check clean and render from every prefix as it streams.

Disable through normal configuration:

{ "plugins": ["-opencode.genui"] }