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

With no annotations, the description carries the full burden and does so well: it discloses the returned fields, redirect resolution, a SHA-256 digest, the verdict mechanism with named failure reasons (JS shell, bot challenge, cookie wall, sign-in redirect, error page), and the fact that not_content responses are free. That is unusually rich behavioral context for a fetch tool.

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-loads the action and the returned value, then the limitation, then the verdict behavior — no filler and nothing repeated from the title. The sentence structure is dense but each clause carries distinct information.

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?

No output schema exists, and the description compensates by enumerating the response fields and the not_content verdict shape. Combined with the no-JS limitation, an agent has everything needed to call it and interpret the result 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?

Schema coverage is 100%, so the url example and the api_key fallback/header-precedence rule are already fully documented in the schema. The description adds no parameter-level meaning beyond that, so the baseline 3 applies.

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 ('Fetch a web page') and immediately names the payload ('main text as Markdown') plus the extra fields returned. It is unmistakably distinct from the siblings check_agent_readiness and request_key.

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?

The 'Plain HTTP only: it does not run JavaScript' line and the enumerated not_content cases tell the agent when this tool will fail and therefore when not to reach for it. It stops short of explicitly routing to check_agent_readiness as the alternative for verifying a site is fetchable.

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