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

Annotations only mark destructiveHint/openWorldHint; the description goes far beyond by disclosing hard caps (384KB response, 64KB body, 12s, 3 redirects), SSRF protection, cookie behavior, the billing distinction between upstream 4xx/5xx (charged) and proxy errors (not), the $0.01 x402/USDC-on-Base cost, and a prompt-injection warning. That is unusually rich behavioral context an agent cannot get from the structured fields.

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?

A dense single paragraph, but front-loaded with purpose and ordered sensibly (modes, return shape, limits, security, billing). Nearly every clause carries signal; a bulleted structure would have helped readability, but nothing is padding.

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, yet the description enumerates the return fields (status, filtered headers, body as text/base64, contentType, finalUrl, elapsedMs), plus limits, security posture, error/billing semantics, and payment requirement. An agent has everything needed to call it and interpret results.

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 baseline is 3, but the description adds the calling convention the schema does not encode: method defaults to GET, headers are JSON, and the POST-JSON-body mode is an alternative envelope carrying url/method/headers/body. That clarifies how the four parameters combine at call time.

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: 'HTTP/API proxy for public URLs', with the dual invocation modes spelled out (GET with url vs POST JSON {url, method, headers, body}). The purpose is unmistakable, but the description never names or contrasts itself with close siblings such as 'fetch' or 'search', leaving the agent to infer the distinction.

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 explains HOW to invoke (GET vs POST JSON) and states one exclusion ('private hosts blocked', 'no cookies sent'), but gives no explicit when-to-use/when-not guidance relative to alternatives like fetch or search. Usage is implied by the mechanics rather than routed.

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