Compose Preview Catalogs

ui_builder_fork_design

Make a new design from one revision of another — yours to edit, owned by you, with its parent recorded: the fork's forkedFrom (design, revision, document digest) and the parent's forks both show in ui_builder_get_links. A fork is not a branch: it never inherits the parent's canonical home and nothing flows back on its own, so tell the person it exists and bring a chosen change back with ui_builder_apply on the parent. Needs write access on this server and read access to the parent.

Input Schema

TableJSON Schema

Name	Required	Description
`title`	No	The fork's title. Defaults to the parent's, marked with the revision.
`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	The design to fork.
`revision`	No	A retained revision. Omit for the current one.
`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.
`newDesignId`	No	The fork's id. Defaults to one derived from the parent; an id already taken is refused.

Output Schema

TableJSON Schema

Name	Required	Description	Default
`home`	No
`title`	Yes
`schema`	Yes
`summary`	Yes
`designId`	Yes
`revision`	Yes
`forkedFrom`	Yes
`ancestryRecorded`	Yes

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"
+}

AddedOct 1, 2026

TDQS

A4.6/5.0

Behavior5/5

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

No annotations are provided, so the description carries the full burden, and it does: ownership of the fork, that the parent link is recorded on both sides and surfaces in ui_builder_get_links, that no canonical home is inherited, that no changes flow back automatically, and the required write/read permissions. These are exactly the behavioral traits an agent needs before invoking a state-creating tool.

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?

Two dense sentences with no filler and the key semantic constraint front-loaded ahead of the mechanics. It is information-rich rather than bloated, though the second sentence is long enough that it could be split for scannability.

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

Completeness5/5

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

For a 7-parameter mutation tool with an output schema, the description covers the semantic behavior (fork vs branch), where fork metadata appears, the access requirements, and the round-trip workflow. Return values are handled by the output schema, so nothing an agent needs is missing.

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 description coverage is 100%, so every parameter is already documented in the schema, including the token/header distinction and newDesignId collision behavior. The description adds only the general notion of forking 'one revision,' which the schema's revision param already conveys, so the baseline 3 is correct.

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?

States a specific verb+resource ('make a new design from one revision of another') and immediately scopes ownership and parentage. It explicitly distinguishes itself from the closest sibling by declaring 'A fork is not a branch,' so an agent can route between fork_design and branch_design without opening schemas.

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

Usage Guidelines5/5

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

Gives explicit when-to-use guidance and an exclusion: a fork 'never inherits the parent's canonical home and nothing flows back on its own,' plus the follow-up path ('bring a chosen change back with ui_builder_apply on the parent'). It also states the access precondition (write on this server, read on the parent).

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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