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

Goes well beyond annotations: discloses that only names and sizes are returned, never header values; that results are estimates; the 1-4s typical runtime and 25s wall-clock limit; cost ($0.002) and free tier (10/day per IP); and a prompt-injection caution about treating page text as untrusted. These are exactly the behavioral facts an agent cannot get from readOnlyHint/idempotentHint alone.

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?

Purpose is front-loaded and nearly every clause carries information (returns, cost, timing, safety). It is dense to the point of being a run-on, and the 'limit overrides' phrase costs clarity, but there is little pure filler.

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?

An output schema exists, yet the description still sketches the return shape, error behavior, cost model, timing bounds, and trust posture. For a single-parameter read-only measurement tool, nothing material 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?

Schema coverage is 100% for the single url parameter, so baseline is 3. The description reinforces constraints (public HTTPS, port 443, no redirects) but also mentions 'limit overrides' that do not appear as parameters in the schema, which adds slight ambiguity rather than clarifying argument semantics.

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 (measure) and resource (response headers) and names the exact comparison targets (nginx, aiohttp, Node fetch, Python limits). This distinguishes it from siblings like check_security_headers and get_page_meta without opening either 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 operating context: one unpaid public-HTTPS GET, no redirects or body read, and invalid/unreachable hosts return 422 without charge. It does not explicitly name a sibling alternative or state when-not to use it (e.g., vs check_security_headers), which keeps it below a 5.

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