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

Annotations mark destructiveHint=true, and the description adds meaningful behavioral context beyond that: it explicitly says 'MUTATES', may create an invoice, and may return a payment URL. This informs the agent of side effects and potential need for payment action, though it does not fully spell out all downstream consequences.

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 description is two sentences with high information density: it front-loads the mutating nature, names the operation, gives the API endpoint, and lists the return shape. No filler or repetition exists.

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 complex 10-parameter tool with no output schema, the description provides essential context: mutation, side effects, endpoint, and return fields. It is slightly incomplete in not mentioning when to prefer preview_attach or preconditions, but the schema and annotations cover most invocation details.

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%, so every parameter is already documented in the input schema. The description adds no supplemental parameter meaning, but the baseline of 3 applies because the schema carries the full explanatory burden.

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 identifies the action: attaching/subscribing a plan to a customer, and explicitly flags that it mutates billing data and may create an invoice or return a payment URL. However, it does not explicitly distinguish itself from sibling preview_attach, relying on the 'MUTATES' emphasis to imply the contrast.

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 no guidance about when to use this tool versus alternatives, and notably preview_attach exists as a likely non-mutating counterpart. There are no prerequisites, exclusions, or conditional use cases stated, so an agent must infer usage from the tool name and schema.

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