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

Annotations cover the safety profile (readOnly, idempotent, openWorld, non-destructive), and the description goes well beyond them by disclosing the payment/auth requirements: x402 pay-per-call in USDC on Base, $0.03 per call, an ~8 ms payment challenge, and the exact PAYMENT-SIGNATURE header needed. This is exactly the kind of auth/cost context an agent cannot get from 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?

Front-loads the core purpose, then flows into payment mechanics. The payment sentence is dense but earns its place because it is a genuine invocation prerequisite; only minor trimming is possible.

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?

With no output schema, the description correctly summarizes the return shape (schema-matched JSON plus page title and source) and fully documents the payment flow. It omits error behavior and rate limits, a minor gap for an OpenWorld fetch tool.

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 only 33%, and the description adds real meaning only for the 'schema' parameter ('return JSON matching your schema'), which is the most non-obvious input. The 'url' and 'max_chars' parameters gain nothing from the description beyond their schema definitions, so it only partially compensates for the coverage gap.

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 (fetch) and resource (public URL) plus supported content types (HTML article, PDF, JSON) and the return shape (JSON matching your schema, with page title and source). This clearly distinguishes it from siblings like extract, summarize, and translate, which serve different transformations.

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 implies usage (public URLs only) and conveys cost/payment context, but never states when to choose this over the sibling 'extract' tool or when not to use it (e.g., non-public or authenticated URLs). Usage is inferable rather than explicit.

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