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

Annotations already declare readOnlyHint=true and openWorldHint=false, so safety is covered. The description adds real context beyond that: the relationship to watch_listing as its read counterpart, the shape of the returned data, and the pricing tier ($0.01/call, included in certain plans) which matters for cost-aware agents. It stops short of describing pagination or failure behavior.

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 resource identity, then relationship, then economics. The pricing sentence is somewhat dense but earns its place for a paid API. No filler or restated title.

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 does the work of describing return contents (watched listings, their events, start dates) and the paid-call expectation. For a trivial read-only list tool this is nearly complete; only pagination/ordering behavior is unstated.

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?

There is a single optional 'context' parameter with 100% schema description coverage, and the schema already explains that it is never used to rank and is read only if a result is wrong. The description adds nothing to parameter meaning, so the 3-baseline for full schema coverage applies.

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 (the listings you are watching) plus the payload contents (events registered and when you started). It also draws a clean boundary against the sibling watch_listing by calling itself 'the read half', so an agent can separate the two without opening either schema.

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?

Explicitly prescribes when to call it — 'before registering another' — and states the failure mode it prevents (duplicate watches, or assuming a watch exists that never took). This is actionable routing guidance rather than implied context.

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