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

Despite annotations already declaring idempotentHint and destructiveHint, the description adds substantial non-obvious behavior: the error is identical whether an id belongs to someone else or does not exist, cancelling frees a slot in a free key's watch limit, the call is never billed, and a blank key returns a signup link. These are real operational disclosures that annotations cannot convey, and nothing contradicts them.

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 definition is dense but nearly every clause carries useful information (idempotency, error semantics, billing, auth). The opening clause is awkwardly worded, and the examples and constraints are somewhat packed together, but the tool-relevant facts are front-loaded.

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 supplies the response shape ({id, canceled}), the idempotency guarantee, error behavior, billing and quota effects, and the auth requirement. An agent has everything it needs to invoke this correctly for a mutation tool.

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 50% (watch_id has no schema description), so the description must compensate, and it does: it specifies that watch_id comes from watch_company or list_watches and that foreign/nonexistent ids produce the same error. It also references the key requirement, complementing the schema's deprecation note for plane_api_key.

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 identifies a specific verb and resource (cancelling a watch) and even shows the input/output transformation ({watch_id: 42} -> {id: 42, canceled: true}). It implicitly distinguishes itself from siblings by naming watch_company as the id source and list_watches as the way to enumerate ids, though the leading phrase 'WHEN a watch should stop firing' is slightly elliptical rather than a clean verb statement.

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?

It gives clear context for when this applies (a watch should stop firing) and explains how to obtain the required id from watch_company or list_watches. It stops short of explicit when-not guidance or naming a sibling it replaces, but the surrounding conditions are unambiguous.

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