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

Annotations already declare readOnlyHint, idempotentHint, openWorldHint=false and destructiveHint=false, so safety is covered. The description adds one piece of non-obvious context: it also returns FTC click-to-cancel rule status and UK rules (uk_rules). That is useful but thin, and no return shape or pagination is described.

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?

The first two sentences ('Cancel My Sub. Every subscription Cancel My Sub covers.') restate the name and title with no added information, which is waste before the genuinely useful usage examples and rules-status note.

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 simple read-only listing tool with no output schema and fully-documented optional params, the description covers purpose, trigger queries, and an unexpected extra return payload. Nothing critical for calling it correctly is missing.

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 description coverage is 100% with only two optional params, so the schema already fully documents country and category. The description adds no syntax or filtering semantics beyond what the schema provides, making the baseline 3 appropriate.

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 resource (every subscription Cancel My Sub covers) and the example phrasings ('which subscriptions can you help me cancel?', 'what gyms do you know?') make the listing intent unambiguous. It does not explicitly contrast with siblings like get_cancel_steps, but the verb+resource is clear.

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 explicit trigger phrasings ('Use for...'), which is genuine usage context rather than inference. There are no exclusions or named alternatives, so it stops short of the top band.

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