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

Annotations already declare readOnlyHint=true, idempotentHint=true, and destructiveHint=false, so the safety profile is covered. The description adds valuable behavioral context beyond the schema: it reports only verdict changes at a given path, includes sitemap additions, and indicates whether parse errors went up or down. It does not go into details like rate limits or exact output shape, but it is fair given the annotation coverage.

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 description is compact but packed with useful information, including a runnable first-call snippet and an example. It is front-loaded with the most important routing callout. The embedded JSON-RPC snippet is a bit long and could have been shortened, but it directly supports correct first invocation, so it earns its place.

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 read-only diff tool with 100% schema coverage and no output schema, the description covers the input semantics, the behavioral scope (verdicts, sitemap additions, parse error trend), and a worked example. It does not specify the exact return format, but since there is no output schema and the tool's goal is clearly stated, this is a moderate gap rather than a severe one.

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%, so the baseline is 3. The description adds meaning by explicitly naming the example values (before='User-agent: *\nAllow: /\n', after=your edited file, path='/') and by clarifying that before is 'the old robots.txt' and after is 'the new robots.txt'. That mapping helps an agent avoid swapping the two parameters, which is meaningful semantic value beyond the raw 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?

The description states a specific task — diff two robots.txt versions and report only crawler verdict changes at a given path — which clearly distinguishes it from text-diff or linting siblings. It also gives an explicit example of the core before/after/path semantics, making the tool's purpose concrete.

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?

The description explicitly says 'FIRST CALL, needs nothing' and embeds an exact JSON-RPC invocation for the prerequisite scan tool, which strongly guides when to use this tool. It also frames the use case ('did my edit do what I meant...') and contrasts with reporting text differences, helping an agent choose this over lint or check tools.

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