Compose Preview Catalogs

ui_builder_react_to_comment

React to one comment with an emoji, or take the reaction back with on: false. The lightest thing you can say: 👀 on a comment you have just picked up, 👍 on a fix somebody made, where a reply would be noise in a thread a person has to read. commentId is the id of a comment inside a thread, from ui_builder_list_comments. Reacting also acknowledges that thread for you, so it counts as the lightest acknowledgement; it says nothing about whether the question is settled.

Input Schema

TableJSON Schema

Name	Required	Description
`on`	No	False takes your reaction back. Defaults to true.
`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
`reaction`	Yes	One emoji, at most 24 characters.
`agentName`	No	Optional agent/client name shown to design viewers; self-reported.
`commentId`	Yes	The comment to react to, from its thread's `comments`.
`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

A4.3/5.0

Behavior4/5

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

With no annotations the description carries the full burden, and it does disclose key behavior: on:false is reversible, reacting has a side effect (it 'acknowledges that thread for you'), and it is bounded ('says nothing about whether the question is settled'). It does not address auth/permission requirements beyond pointing at the token parameter's schema text.

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 action is front-loaded in the first clause, and the emoji examples earn their place by illustrating the intended usage. It is somewhat conversational and longer than strictly necessary, but no sentence is pure filler.

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?

An output schema exists, so return values need not be described. The description covers the action, its inverse, its side effect, and where commentId comes from, which is sufficient for a 7-parameter tool whose remaining params are documented in the schema.

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

Parameters4/5

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

Schema description coverage is 86%, so the baseline is 3, but the description adds provenance the schema lacks: commentId 'is the id of a comment inside a thread, from ui_builder_list_comments'. The on:false behavior and reaction semantics are largely restated from the schema, so the gain is modest.

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 and resource ('React to one comment with an emoji') plus the inverse action ('take the reaction back with on: false'). It distinguishes itself from siblings by naming its role as 'the lightest acknowledgement', implicitly contrasting with a full reply or explicit acknowledge.

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?

Gives concrete when-to-use examples ('👀 on a comment you have just picked up, 👍 on a fix somebody made') and a when-not condition ('where a reply would be noise in a thread a person has to read'). It stops short of explicitly naming the alternative tools (ui_builder_post_comment, ui_builder_acknowledge_comment), so routing is inferred rather than stated.

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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