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

The description goes well beyond the readOnly/idempotent annotations by disclosing the explicit per-symbol error behavior, the $0.005 USDC cost via x402 on Base, the payment-challenge edge case, and the no-data/no-settlement guarantee. This is rich behavioral context an agent needs before calling.

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 front-loaded with purpose and usage, then adds error handling, cost, and routing details. It is a bit dense, especially around the payment model, but each sentence conveys an operationally relevant fact with little waste.

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 simple one-parameter, read-only tool, the description covers purpose, asset-limit, error behavior, cost edge cases, and the equivalent HTTP route. There is no output schema, and the response shape is not described in detail, but the description is adequate for correct invocation.

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?

The input schema already documents the symbols parameter with examples and a default, and coverage is 100%. The description adds extra meaning by stating the 'up to ten' asset limit and clarifying that prices are USD spot values, which is not fully captured in the schema.

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 and resource: it returns Coinbase spot prices in USD for crypto assets. It clearly scopes the tool to 'current' prices for up to ten assets, distinguishing it from sibling price-oriented tools like defi_token_prices and fx_reference_rates.

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 explicitly says 'Use this for a current crypto price,' giving clear guidance on when to invoke the tool. However, it does not mention alternative tools or conditions where a sibling would be preferable, so it stops short of full when/when-not guidance.

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