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

Annotations already declare destructiveHint=true and readOnlyHint=false, but the description adds substantive behavior beyond them: it is a read-modify-write of the whole v2 record, existing associatedActivityTypes are replaced, and the operation is irreversible. The GET/replace/PUT sequence is exactly the kind of context annotations cannot convey.

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?

Purpose is front-loaded, but the text is repetitive: the 'old dedicated default-gear endpoint is dead' claim appears twice and there is tangential API lore. Sentences are dense with useful content but could be tightened by roughly a third without losing meaning.

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?

For a destructive, zero-schema-coverage mutation with no output schema, the description supplies the essential context: irreversibility, the read-modify-write nature, key casing, and the clear semantics. The only real gap is what gearUUID refers to and any permission requirements.

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?

Schema coverage is 0%, so the description must carry the parameters, and it does: it specifies activityTypeKeys must be lowercase ('running'), matching createGear and not the upper-cased setGearDefault form, and that '[]' clears the defaults. gearUUID is only implied by the GET path, so it is not a full 5.

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?

States a specific verb and resource: 'Sets which activity types default to this gear.' It goes further by naming the mechanism and contrasting with related operations (createGear, the dead setGearDefault), which helps the agent place it among gear tools. Not a 5 because the purpose statement is muddied by repetitive endpoint lore rather than a crisp one-line summary.

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?

Provides a real usage cue: 'IRREVERSIBLE: confirm with the user before calling.' That is genuine when-to-act guidance. However it gives no explicit routing against alternatives (e.g. add_gear_to_activity vs this), only a safety precondition, so it lands at minimum-viable-plus.

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