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

Annotations only cover read-only and open-world, but the description adds real operational context: anonymous access, per-IP rate limiting, refusal of private/reserved addresses, and the fact that a result is one sample rather than continuous uptime. These are exactly the traits an agent needs before calling.

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?

Three dense sentences, front-loaded with the core verdict and its fields, followed by routing guidance and constraints. No filler and nothing repeated from the schema or annotations.

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 field-level return documentation is unnecessary, and the description still names the key fields. Combined with scope, routing, and access constraints, an agent has everything needed to call this correctly.

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 at 100% schema description coverage, including an example URL, so the schema already carries full meaning. The description adds no syntax or formatting detail beyond what the schema provides, making the baseline 3 correct.

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 ('Checks whether a website is up right now') and enumerates exactly what the verdict contains: up/down, HTTP status and text, response time, server header, redirect count. It explicitly distinguishes itself from siblings response_time, http_headers and redirect_check, so an agent can route without opening any 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 an explicit routing rule ('The usual first call for any is-the-site-down question') and a clear exclusion ('A single sample from one location, not uptime') that names the deeper alternatives for those cases. Both when-to-use and when-not-to-use are covered.

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