Compose Preview Catalogs

ui_builder_preview_catalog_recovery

Dry-run recovery of a design whose stored catalog pin no longer resolves. The server selects the exact currently served pin for the same catalog system and returns a CatalogUpgradePreviewV1 with changes, issues and the hashes required by a later upgradeCatalog mutation through ui_builder_apply. This call never writes.

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.
`designId`	Yes
`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

A4.2/5.0

Behavior4/5

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

With no annotations, the description carries the safety burden and does so well by stating 'Dry-run' and 'This call never writes.' It also describes the returned preview artifact and its role as preparation for a later mutation, though it does not mention authentication or token requirements beyond what the schema provides.

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

Conciseness5/5

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

Three tight sentences, front-loaded with the core dry-run recovery purpose, followed by return details and the non-write guarantee. Every sentence earns its place.

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

Completeness4/5

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

Given that an output schema exists, the description needn't explain return values in depth, but it helpfully names CatalogUpgradePreviewV1 and its key contents. Combined with the no-write statement and the apply relationship, this is nearly complete for a preview tool, with only minor auth/prerequisite context left to the schema.

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 75%, with token, agentName, and agentModel documented in the schema. The description mentions the design and catalog context but adds no parameter-level details, and designId itself has no schema description, so the description does not compensate for that gap.

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

Purpose5/5

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

The description states a specific operation ('Dry-run recovery') and resource ('a design whose stored catalog pin no longer resolves'), and it distinguishes the tool from the later mutation by naming `upgradeCatalog` through ui_builder_apply. An agent can tell this is the non-mutating recovery preview, not the apply step.

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

Usage Guidelines4/5

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

It clearly identifies the triggering scenario ('whose stored catalog pin no longer resolves') and explains the intended follow-up path through ui_builder_apply. It stops short of explicit when-not-to-use guidance, but the context strongly implies the correct usage condition.

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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