Message Content Types (Segments) — and how to add your own
An assistant turn is a list of typed segments — text, thinking, code, a tool call, an error, or a type you register yourself (generative UI) — each drawn by its own renderer.
On this page
A segment is data, not an element: the typed pieces an assistant message is made of, each drawn by its own renderer. One turn can carry several — reasoning, then a tool call awaiting approval, then code, then prose.
- text — Text segment - plain text content
- thinking — Thinking/reasoning segment - collapsible.
- code — Code segment - syntax highlighted code block Highlighting is a plugin you opt into; with none installed the block renders plain, which is what core’s zero-dependency promise costs here.
- error — Error segment A failure card inside the turn that produced it, rather than a toast somewhere else on the page — so the reader can see which question failed.
- custom — Custom segment - one escape hatch for the views an app draws itself.
- tool_call — Tool call segment - rendered while waiting for a tool handler to resolve
Two seams make the list yours: registerSegmentRenderer
draws a type of your own (a weather card, a domain widget — generative UI), and
registerStreamBlock teaches the
streaming parser a tag grammar that produces it.