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

Beyond the readOnly/openWorld/idempotent hints, the description discloses concrete behavioral constraints: SSRF-style address refusals, per-hop redirect re-validation, and a specific monetary cost via x402. This materially helps an agent predict side effects and prerequisites.

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?

Two sentences, both purposeful: the first states the operation and options, the second adds security and cost constraints. Every sentence earns its place and no filler exists.

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?

Given the annotations, output schema, and full parameter documentation, the description covers the remaining operational essentials: what it fetches, how to narrow, security restrictions, redirect behavior, and cost. No critical invocation detail 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 description coverage is 100%, so the schema already documents url, format, and selector. The description adds only interpretive flavor ('readable text', 'optionally narrowed by selector') without providing substantive new parameter meaning.

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 uses a specific verb ('Fetch') with a resource ('a URL') and states the output ('readable text or markdown'), making the core function unambiguous. It inherently differentiates from siblings like pdf_parse by resource type.

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 description makes the general usage context clear and states that private, loopback, and link-local URLs are refused, which is an explicit when-not condition. It does not name alternative tools or scenarios where a sibling would be preferred, so the guidance falls short of explicit routing.

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