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

Annotations only declare readOnlyHint=true, so the description carries the real disclosure burden and delivers: anonymous access, per-IP rate limiting, refusal of private/reserved address space, single-location/single-sample semantics, and the explicit caveat that a failure is not proof of downtime.

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?

Front-loaded with the core question and verdict, then progressively adds scope, limitations, sibling routing, and access constraints. Dense but every sentence earns its place with no 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 so return values need no explanation. The description still supplies the sampling caveat, sibling alternatives, and access/rate-limit constraints — everything an agent needs to call this correctly and interpret results.

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?

Single required 'url' parameter is fully documented in the schema (100% coverage) with an example. The description adds no syntax beyond the schema, so the baseline of 3 applies — the schema does the heavy lifting here.

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?

Opens with a specific verb+resource framed as a question ('Is a website up right now?') and enumerates exactly what the call returns (up/down verdict, HTTP status/text, response time in ms, server header, redirect count). It clearly distinguishes itself from siblings by naming what it consolidates in one call.

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?

Explicitly states when to use it ('Start here for any is-the-site-down question') and routes to alternatives by condition: response_time for timing breakdown, http_headers for headers, redirect_check for the chain. It also warns that a failure here is a single-sample result, not uptime.

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