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

Annotations cover the safety profile (readOnlyHint=false, openWorldHint=true, idempotentHint=false), and the description adds substantial context on top: $0.004 USDC per request, x402 payment requirement, baseline creation and cross-buyer sharing, and an explicit warning that returned URLs are untrusted. This is exactly the kind of behavioral detail structured fields cannot convey.

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?

Five short sentences, purpose front-loaded, each carrying distinct information (return shape, baseline behavior, alternative, cost, security note). Only the 'FetchDelta:' product prefix is mild redundancy with the tool name.

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?

No output schema exists, and the description states the return content (added/removed lines and change previews). Payment, baseline semantics, and untrusted-URL handling round out everything an agent needs 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 0% and there is one parameter, so the description must compensate. It implies a single public URL ('one public web page'), which matches the array's maxItems=1 constraint, but adds no format, protocol, or accessibility constraints beyond that. Marginal value over the schema.

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 (compare) and resource (one public web page vs. its previous stored snapshot), and explicitly names the sibling it is not (page-watch-30d for a private daily watch). An agent can distinguish it from siblings without opening any schema.

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 context: first call creates a baseline, later calls reuse the shared URL baseline, and it names page-watch-30d as the alternative for a private daily watch. It stops short of explicit when-not-to-use cases or prerequisites beyond the alternative.

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