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

With no annotations, the description carries full burden and does well: it discloses that no download occurs, lists returned data, mentions no API key, and specifies pricing ($0.005 per call, x402/USDC). It omits rate limits or error-handling behavior, but covers key operational traits.

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?

The description is a single dense sentence that front-loads the core use case and then lists returned data. Every clause earns its place, though the sentence is long and could be split for readability without losing content.

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, so the description must explain return values; it does so thoroughly by listing HTTP status, redirect chain with codes, final URL, HTTPS status, content type/size, and security headers. It also covers cost and payment method, making it complete for an agent to invoke 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 both parameters are already documented. The description adds meaning by clarifying 'one URL' (single, not batch) and 'without downloading' (implying the default HEAD method), but does not elaborate on the method parameter beyond what the schema provides.

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 explicitly states the tool checks a URL without downloading it, enumerating specific outputs (HTTP status, redirect chain, final URL, HTTPS, content type/size, security headers). It clearly distinguishes itself from web_read by contrasting 'without paying for the page', making the resource and scope unambiguous.

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 opening clause 'Use when an agent must decide whether a link is alive and where it really lands, without paying for the page' gives a clear use case. The phrase 'Built for going through a list of links one at a time' adds contextual usage guidance, but the description does not explicitly name a sibling alternative (e.g., web_read) or state when not to use it.

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