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

Annotations already cover safety (readOnly, idempotent, non-destructive), but the description adds real behavior: UK answers carry region 'UK' and uk_rules, and a US-only service queried from the UK is tagged 'US only'. That conditional output behavior is not derivable from the annotations or schema.

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?

Front-loaded with the core purpose and return contents, then usage examples, then the regional caveat. The example list is slightly long but each example disambiguates a different subscription type (gym, streaming, membership), so it earns its space.

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?

With no output schema, the description must convey return shape, and it does (page, steps, catches, cheaper option, region/uk_rules). For a 3-param read-only tool this is essentially complete; only explicit sibling routing 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 coverage is 100%, so baseline is 3, but the description adds cross-parameter meaning the schema does not spell out — how country interacts with service (US-only + UK caller → region 'US only') and what renews_on produces in the answer. This genuinely supplements the structured fields.

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 states a specific verb+resource ('How to cancel one subscription') and enumerates what it returns (official page, steps, catches, cheaper option), which is well beyond a tautology. It does not explicitly distinguish itself from siblings like get_cancel_reminder, but the purpose is unambiguous.

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 example utterances ('how do I cancel Netflix?', 'cancel my PureGym') give an agent clear triggering contexts, which is strong implied when-to-use guidance. It stops short of naming alternatives or stating when not to use it versus get_cancel_reminder or list_services.

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