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

Annotations already declare readOnlyHint=true and openWorldHint=true, so safety is covered. The description adds genuinely useful context the annotations do not: the exact output formats per unit and the paid-call behavior ($0.002 USDC per call, x402), which an agent must know before invoking. It omits size limits and error behavior, so not a 5.

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?

Two sentences, no filler: the capability and output formats come first, the use cases next, and the pricing last. Every clause carries information an agent needs.

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?

There is no output schema, and the description compensates by summarizing the return shape (diff format, counts, similarity score). Cost is disclosed. Only limits on input size, rate limits, and failure modes are absent, which are minor for a two-text comparison tool.

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 goes further by explaining what each `unit` value produces (unified line diff vs. inline word diff with marker syntax), which directly informs the parameter choice rather than just restating it.

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 (two texts), then enumerates the concrete outputs: unified line diff, inline word diff with [-removed-]/{+added+} markers, add/remove counts, and a similarity score. This is enough to separate it from image_diff at a glance.

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?

Names concrete use cases (contract redlines, document versions, code) which tells the agent the domain this tool is for. It does not name a when-not condition or point to an alternative sibling, so it falls short of the 5 bar.

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