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

The description goes well beyond readOnlyHint by enumerating specific fault types (misspelled directives, noindex unsupported since 2019, relative Sitemap URLs, BOM) and stating the output shape: 'Each finding carries the line number and the fix.' This gives an agent a concrete model of behavior without needing to invoke the tool.

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 entire description is one sentence that front-loads the action and follows with a compact list of fault categories and the output contract. No filler or redundant restatement. Every clause adds operational detail.

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 single-parameter read-only tool with no output schema, the description covers input, processing intent, and return-value contract (line number + fix). It lists enough fault categories to set expectations, and the absence of an output schema is compensated by the explicit per-finding description. No critical detail is missing.

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?

The input schema already documents robots_txt as 'The contents of the robots.txt file' with 100% coverage. The description adds only that the user pastes the content, which reinforces the inline-string expectation but doesn't add format, encoding, or size details. Baseline 3 is appropriate.

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: 'Parse a robots.txt you paste and report every fault...' It lists concrete fault categories and output details, making its function unambiguous. Its scope as a generic whole-file linter distinguishes it from siblings like check_path_allowed or merge_policy.

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 phrase 'a robots.txt you paste' signals the input mode and when to use the tool: when the user has file contents to validate. It does not explicitly reference sibling tools or state when not to use it, but the lint-focused purpose supplies clear context. Missing explicit exclusions/alternatives prevents a 5.

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