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

Annotations already establish read-only, idempotent, non-destructive, closed-world behavior, so the description's remaining job is auth and cost, which it does well: mts_ key via header or apiKey argument, free trial tier at 50 calls/7 days, and paid plan at 1 USDC/30d for 1,000 calls via x402. It does not disclose what statuses are returned or whether the watch status is eventually consistent, which would have pushed this higher.

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?

Three short sentences with the core purpose front-loaded and the auth/pricing caveat following. The X-API-Key/apiKey and 1 USDC/30d pricing details are dense but arguably necessary for a paid API, so little is wasted.

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 two-parameter, zero-required status read with full schema coverage and rich annotations, the description covers the main practical gap (authentication and cost). The residual omission — what the returned status actually looks like or means, in the absence of an output schema — is minor for a simple status lookup.

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 both apiKey (mts_ prefix, header alternative) and watchId (stw_ from settle_watch) are already fully documented in the schema. The description merely echoes the apiKey requirement and the missing-key fallback rather than adding new semantics, so the baseline 3 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?

"Status of a settlement watch" is effectively a restatement of the title "Settlement watch status" — a noun phrase with no distinct verb and no differentiation from the sibling settle_watch, which presumably creates the watch. An agent learns the resource but not precisely what operation is performed (fetch latest state? poll for completion?).

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 useful prerequisite routing: a key is required, and without one the agent should call settle_trial_key. However, it offers no guidance on when to use this versus settle_watch, settle_key_status, or settle_gate_complete — the selection decision among sibling settle tools is left to inference.

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