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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive, closed-world), and the description adds genuinely new behavior: default sort order, the fields each item carries, the no-`watchId` fallback, and an authentication requirement ('Needs a free SnoopScan key'). It stops short of describing volume/pagination behavior or what an empty result means.

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 core behavior is front-loaded in one dense sentence, and the filter/fallback note follows logically. The trailing 'Needs a free SnoopScan key.' is a stray fragment detached from the main block, slightly hurting structure but costing little length.

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 three-parameter read-only list tool with an output schema, the description covers purpose, ordering, filters, and the auth prerequisite, so an agent can invoke it correctly. The remaining gaps (limit/paging semantics, whether statuses are mutually exclusive) are minor given the output schema documents the result shape.

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?

With 0% schema coverage, the description carries the full burden and does well on two parameters: it enumerates the `status` values (new, seen, saved, dismissed) that the schema lacks as an enum, and explains `watchId`'s effect including its null-case. `limit` is never mentioned, so one of three parameters remains undocumented in both schema and description.

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 gives a specific verb and resource ('List the items this account's listing watches have found') plus scope details: newest-first ordering and the per-item fields returned (price, place, distance, match reason). It does not name a sibling to contrast with, so an agent can't tell from the text alone whether `watchListings` is the setup counterpart or an alternative view.

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 states a filtering condition ('Filter by `watchId` or `status`') and a fallback behavior ('With no `watchId` the account's watches are listed first'), which implies when the tool is useful. It never says when to prefer another tool or what precondition must hold (e.g., watches must exist / be configured) before calling, leaving the alternative-selection decision to inference.

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