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

Beyond the annotations (readOnlyHint=false, idempotentHint=false), it discloses the non-idempotent compounding behavior (extension starts from current expiry and is capped at 400 days), per-target pricing, and the critical client-side spendControls failure mode where the caller's own x402 client rejects the quote. It also specifies the api_key fallback's distinct error behavior (credits error instead of an x402 quote). No contradiction with annotations.

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?

Dense but every sentence earns its place: core action, expiry window, duration freedom, 400-day cap, itemized pricing, and payment caveats are all load-bearing. The most critical client-side failure warning sits after the pricing that justifies it, and the length is proportionate to the tool's payment complexity.

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 payment-bearing mutation with five parameters, the description covers renewal eligibility, duration semantics, exact pricing, both payment routes, and a non-obvious client-side rejection mode. The output schema covers return values, so nothing an agent needs to invoke this tool correctly is missing.

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 100%, so the baseline is 3, but the description adds real meaning: cibles must repeat the exact watched targets because the quote is computed from it, duree is independent of the original duration, and api_key selects a credits-based payment path with a distinct failure mode. The spendControls warning explains why x_payment can fail on a well-formed request.

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?

Opens with a specific verb+resource+scope: 'Renew a watchlist for 30, 90 or 365 more days (possible until 7 days after expiry).' The renewal semantics are unambiguously distinct from the sibling trio create/get/stop_surveillance_watch. Duration options, expiry window, and the 400-day cap make the purpose concrete rather than a generic 'renews a watch.'

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?

Provides clear operational context: renewal is possible until 7 days after expiry, duration is a free choice, and the extension starts from the current expiry date. It does not explicitly name alternatives or exclusions (e.g., 'use stop_surveillance_watch to cancel, create_surveillance_watch for a new watch'), so sibling routing is left implied.

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