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

Annotations only supply readOnlyHint=true, so the description carries real weight here and delivers: anonymous access, per-IP rate limiting, refusal of private/reserved address space, the meaning of partial=true and its effect on the average, and the no-browser execution model. These are operational traits an agent cannot infer from the annotation or schema.

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?

Five dense sentences, each carrying distinct information: purpose and outputs first, then partial semantics, then the rendering caveat, then snapshot limitation and access constraints. Slightly list-like toward the end, but every clause 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?

Even though an output schema exists and would cover return values, the description still frames what comes back and, more importantly, covers the execution model, access model and interpretation limits that structured fields cannot express. Nothing an agent needs to call this correctly and interpret the result 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?

There is a single parameter (url) with 100% schema description coverage, so the schema already documents the input. The description adds no syntax, format or constraint detail about the URL beyond the schema's example; its parameter-adjacent note about partial=true refers to an output field, not an input. Baseline 3 is appropriate when the schema does the work.

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 ('Measure how fast a URL answers') plus the exact output shape (samples, min/avg/max ms, HTTP status, up flag). It actively distinguishes itself from render-based siblings by declaring 'no browser runs, so nothing here reflects JavaScript, assets or Core Web Vitals,' which separates it from page-rendering tools and clarifies it is not ping_test or a full website_status check.

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 usage context ('one call is a snapshot, not a trend') and the boundary condition for when this is the right instrument ('measures the response, not the rendered page'). It stops short of naming a specific sibling to use instead for rendered-page measurement or trend tracking, so routing is implied rather than explicit.

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