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

Beyond readOnly/idempotent annotations, the description discloses SSRF protections ('private, loopback and link-local addresses are refused, and every redirect hop is re-validated') and a concrete cost/payment model ($0.010 USDC via x402 or credit token). These are non-obvious behaviors an agent must know before invoking.

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?

Three sentences with no filler: main capability first, then security constraint, then cost/payment. Every sentence adds distinct value, and the structure front-loads the action an agent needs to identify the tool.

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?

For a four-parameter tool with full schema coverage, an output schema, and readOnly/idempotent annotations, the description adds the missing operative constraints: network restrictions, redirect safety, and payment/credit behavior. Nothing essential for correct selection or invocation is omitted.

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, selector, and credit_token. The description adds lightweight context for selector ('narrowed by CSS selector') and payment, but does not materially extend the parameter semantics beyond what the schema provides; 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?

Description uses a specific verb-resource pairing: 'Fetch a URL and return readable text or markdown, optionally narrowed by CSS selector.' This clearly differentiates scrape from siblings like pdf_parse or meetings_search; an agent knows exactly what resource it acts on and what it produces.

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 tool's usage context is clear: fetching a URL for readable text/markdown, with optional CSS selector. It does not name competing tools for exclusion, but it does give conditional payment guidance ('call credits_trial for free credit if you have neither'), which helps an agent decide when a prerequisite is missing.

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