Compose Preview Catalogs

ui_builder_export

Export a design. compose returns the Kotlin the generator writes, or — when the design holds something it cannot express — diagnostics naming each reason. This is the same gate the browser's code pane shows, so an agent and a designer get the same answer about the same design.

Input Schema

TableJSON Schema

Name	Required	Description
`token`	No	A grant token from poll_access, when you cannot set the X-Compose-Preview-Token header yourself — an MCP client fixes its headers at connect time, so this is how a token approved during this session is used in it. Prefer the header where you control it.
`format`	No	Defaults to compose. Available formats: compose, svg, png, bundle. Check the catalog exportCapabilities.
`designId`	Yes
`revision`	No
`agentName`	No	Optional agent/client name shown to design viewers; self-reported.
`agentModel`	No	Optional current model name shown to design viewers; self-reported. Omit when unknown.

Output Schema

TableJSON Schema

Name	Required	Description	Default
No arguments

Schema Changelog

Changes observed during successful MCP inspections.

Changed2 schema fields changedOct 4, 2026

addedInput schema / properties / agentModel

Added value: +{
+  "description": "Optional current model name shown to design viewers; self-reported. Omit when unknown.",
+  "maxLength": 80,
+  "type": "string"
+}

addedInput schema / properties / agentName

Added value: +{
+  "description": "Optional agent/client name shown to design viewers; self-reported.",
+  "maxLength": 80,
+  "type": "string"
+}

Changed1 schema field changedSep 30, 2026
- changedOutput schema / (root)
```
Previous value: -nullNew value: +{
+  "type": "object"
+}
```
First observedSep 30, 2026

TDQS

C2.9/5.0

Behavior3/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

No annotations are provided, so the description carries the full burden. It discloses one important behavioral trait: the tool returns either generated code or diagnostics, and it acts as a validation gate matching the browser pane. However, it does not mention permission requirements, token handling, or whether the operation is read-only or has side effects.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness4/5

Is the description appropriately sized, front-loaded, and free of redundancy?

The description is two tight sentences with no wasted words. The first sentence states purpose, the second explains the 'compose' format's outcome and its parity with the browser. It is front-loaded and easy to parse.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness3/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

The tool has 6 parameters, no annotations, and an output schema. The description covers the 'compose' format's behavior but leaves other formats, permission/token semantics, and revision handling unexplained. With an output schema, return-value details need not be repeated, but the gap around multi-format behavior and access control makes it only partially complete.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters3/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema coverage is 67%, so some parameters are documented. The description adds meaning for the 'format' parameter by explaining what 'compose' returns, but it does not address the 'token', 'revision', 'agentName', or 'agentModel' parameters. Baseline 3 is appropriate given the schema handles most parameter descriptions.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose3/5

Does the description clearly state what the tool does and how it differs from similar tools?

The description states it 'exports a design' and clarifies the 'compose' format's behavior, but it never mentions the other formats (svg, png, bundle) that the tool actually supports, nor does it distinguish itself from many siblings like ui_builder_render_native or catalog_render_preview. The core verb+resource is present, but the scope is narrower than the tool's real function.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines2/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

There is no explicit statement of when to use this tool versus alternatives like ui_builder_render_native, ui_builder_validate, or catalog_render_preview. The description implies it is the code-pane gate, but an agent has to infer that context rather than being told. No exclusions or prerequisites are given.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

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