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

Annotations already declare readOnlyHint, openWorldHint, and idempotentHint, but the description adds meaningful behavioral context beyond them: it follows redirects, grades specific headers, refuses private addresses, and states the body is not stored. The privacy note about the body not being stored is especially valuable and not covered by annotations.

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 short sentences, front-loaded with the core action and constraints. Every sentence earns its place with no redundancy or 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?

For a simple one-parameter tool with 100% schema description coverage and an existing output schema, the description provides everything an agent needs: purpose, behavior, constraints, and privacy handling. Nothing essential 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%, and the schema itself already documents the only parameter, including that private addresses are refused. The description repeats 'Public http or https URL' and the private-address restriction without adding new syntax or format details, so 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?

The description states a specific verb+resource: fetch a public URL, follow redirects, and grade five named security headers. This clearly distinguishes it from siblings like check_ssl and check_robots_txt, which target different resources. An agent can identify the exact operation without opening the 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?

It provides clear context ('Fetch a public URL') and an explicit when-not condition ('Private addresses are refused'). However, it does not name alternative tools or explain when to prefer this over check_ssl or inspect_meta_tags, so it falls short of a 5.

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