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

Annotations already cover readOnly/idempotent/non-destructive, and the description adds real behavioral context beyond them: it never calls the paid endpoint and never pays, it performs the same pre-payment validation the API runs, and payment is x402 with no account or API key, USDC on Base. That is exactly the extra detail annotations cannot express.

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?

Four sentences, front-loaded with the outcome (URL, price, network, asset), then inputs, then the validation behavior, then the payment model. Nothing is redundant and no sentence is filler.

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 2-parameter, nested-object tool with no output schema, the description explains what is returned (URL, price, network, asset), how params are validated, and the payment mechanics. An agent has everything needed to call it correctly and interpret the result.

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%, with the endpoint enum and the params object fully documented in the schema itself, so the baseline is 3. The description restates that you pass the endpoint key and query parameters but adds no syntax or format detail beyond what the schema already provides.

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 and resource: 'Get the exact URL to call for a paid answer, with its price, network and asset.' The 'paid' framing implicitly separates it from the free siblings (get_free_series, get_sample) without needing to name them.

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?

Makes the use case clear: run your planned endpoint+params here first, because they pass the same free check, so refused or empty queries surface before payment. It stops short of explicitly naming alternatives or stating when NOT to use it (e.g. 'use get_sample for a free preview'), but the context is unambiguous.

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