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

The description goes far beyond the readOnlyHint and openWorldHint annotations by detailing authentication (no account, optional x-credit-token header, free daily call), pricing, the specific index source, and the maxChars limit. It also explains the 402 challenge and that it operates on Base over x402, providing substantial behavioral context an agent needs to call it correctly.

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 dense and informative but somewhat verbose, with pricing repeated twice. The main purpose is front-loaded, but the flow jumps between usage, pricing, and pairing, making it slightly less structured. It could be tightened without losing critical details.

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 read-only tool with an output schema, the description covers the essential operational details: input requirements, character limits, pricing, payment method, and its relationship to exa-search. It leaves no obvious gaps for an agent to know how to invoke it correctly, though it could mention error behavior (e.g., missing URL) which is likely covered by the output schema.

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?

While the schema already specifies urls as comma-separated (max 5) and maxChars as 'Max characters per page', the description adds critical constraints: the valid range for maxChars (500..40000) and the default (8000). It also confirms the required input and batch behavior, enhancing the schema's semantic value.

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 it reads pages from Exa's index, not the live web, and returns clean text with title, author, and publish date. It also distinguishes itself from a plain server-side GET by clarifying it uses Exa's crawl, which differentiates it from sibling tools like web_extract or url_extract.

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 provides clear guidance on when to use this tool: after an exa-search, or when a page is blocked from a normal fetch. It doesn't explicitly name alternatives like web_extract for live fetching, but the context is sufficient for an agent to infer the appropriate use case.

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