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

Annotations already provide readOnlyHint and idempotentHint, so the bar is lower. The description adds value beyond annotations by stating it does not fetch prices, charge a wallet, or submit payment, and by outlining the response structure (method, URL, service notes, etc.). No contradiction with annotations.

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 single, information-dense sentence that front-loads the core action and includes return items and constraints. No filler; every clause earns its place.

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?

The description explains the return contents and safety profile, and the output schema exists. It could add an explicit pointer to when to use this versus fetch or get_pricing_info, but the core purpose and limitations are covered sufficiently for an agent to use it correctly.

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 both parameters thoroughly. The tool description does not add any parameter-level meaning beyond what the schema provides, so the baseline of 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?

The description states a specific verb ('Build') and a specific resource ('exact x402-protected HTTP URL for one live market-data request'), and distinguishes itself from data-fetching tools by explicitly noting it does not fetch prices or charge a wallet. It also lists its return contents, making it unmistakable from siblings like fetch or get_pricing_info.

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 when to use this tool (when you need to construct a URL for a paid request) by clarifying it does not execute the request, but it does not explicitly name alternatives or say 'use X instead'. The purpose is clear enough that an agent can infer the distinction, but explicit routing to a sibling would earn a 5.

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