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

Annotations only cover safety/idempotency hints, and the description adds substantially more: scheduled re-checks, receipt-per-change semantics, per-receipt billing with no subscription, the x402 v2 payment-signature header requirement, accepted chains (Base/Arbitrum One), price, and the paid URL. This is exactly the operational context annotations cannot carry.

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 purpose is front-loaded in the first clause, followed by billing and invocation mechanics, which is the right order. Slight redundancy between 'No subscription — pay per fired receipt' and 'Paid tool — $222.00' plus the separate 'Paid URL' line, but nothing is genuinely wasteful.

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 an output schema present, return values need not be explained, and the description fully covers purpose, pricing model, and how to actually invoke the paid endpoint. Combined with 100% schema coverage, an agent has everything required to call this correctly.

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%, and all three parameters (url, idempotency_key, check_interval_hours) are thoroughly documented in the schema itself, including replay and scoping rules for the idempotency key. The description adds no parameter-level detail beyond what the schema already provides, 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?

States a specific verb and resource: it checks a URL on a schedule and fires a signed receipt on every change. An agent can tell it is a standing-monitor tool rather than a one-shot fetch. It does not, however, differentiate itself from siblings like compute_alerts or compute_history, and the title 'Compute History' is a poor match for the name 'watch', which adds friction.

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?

'Use watch when you want standing coverage on a URL' gives an explicit trigger condition and implicitly contrasts with a one-off check. There is no when-not guidance and no named alternative for agents that only want a single check or a different alerting mode.

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