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

Annotations already cover the safety profile (readOnly, idempotent, openWorld, non-destructive), and the description goes well beyond them: change-detection return shape, the 20-line cap on added lines, statelessness ('nothing stored'), SSRF guarding, non-charging on bad input/blocked/upstream errors, the $0.002 x402/USDC-on-Base price, and an untrusted-content warning. That is exactly the kind of operational detail an agent cannot get from 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?

Front-loaded with the core purpose and the required/optional parameter pattern before cost and safety caveats. It is dense and somewhat run-on, packing payment, error-charging, and security notes into one paragraph, but nearly every clause carries decision-relevant information.

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 and no annotations covering returns, the description steps in to specify the response (changed true/false, added lines up to 20, added/removed counts). Combined with the payment, error-charging, and SSRF notes, an agent has everything needed 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 coverage is 100%, so both parameters are already documented, and the description's 'required url' plus 'since (state token from your previous answer)' largely restates the schema. It adds only minor workflow framing (omit on first check) rather than new syntax or format meaning, 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 ('Page change watch API: has a public web page or endpoint changed since your last check') and names the scope (public page or endpoint). An agent can immediately separate this from siblings like fetch or http, which retrieve content rather than reporting a change signal.

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?

Gives clear operating context: GET with required url, optional since taken from the previous answer for this url, and omit it on the first check. It establishes the polling workflow well, but never explicitly contrasts itself with the obvious alternative (fetch) or states when not to use it.

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