Add merge request reaction

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

Annotations already declare readOnlyHint=false and destructiveHint=false, so the description needn't restate that. It adds the scope (MR or its notes) but does not disclose behavioral details like duplicate handling, permission requirements, or side effects. Given the annotation support, the description is adequate but not rich.

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

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

A single, front-loaded sentence with no redundancy. It efficiently states the action, target, and optional sub-target, making it easy to scan.

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

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

This is a simple write operation with an output schema, so the description needn't cover return values. It specifies the core scope (MR or note) and parameter meanings. Slightly more detail on note_id semantics or reaction name format could make it perfect, but it is sufficient for selection and invocation.

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

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

The description explains that 'name' is an emoji and mentions 'one of its notes', which clarifies the optional note_id parameter. This compensates for the 50% schema coverage (project and merge_request_iid are already described). Though it doesn't enumerate accepted emoji names, it gives enough meaning to key parameters.

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

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

The description clearly states a specific action: 'Add an emoji reaction to a GitLab merge request or one of its notes.' It distinguishes this tool from siblings like add_issue_reaction (targets issues) and remove_merge_request_reaction (removes reactions), leaving no ambiguity about its purpose.

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

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

The description gives clear context that this tool is for adding reactions to a merge request or its notes, which differentiates it from issue reactions and removal/list operations. However, it does not explicitly say 'use this when you need to react to an MR' or contrast with alternatives, so it stops short of a 5.

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