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

Beyond the annotations, the description discloses the payment model ($0.005 USDC per call via x402), the unpaid-call behavior (payment challenge instead of data), and the no-data no-settlement policy. It also explains that unavailable assets produce explicit per-symbol errors rather than guessed numbers, adding genuinely useful behavioral context.

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 concise and front-loaded: purpose, then usage, then error behavior, then cost and payment details. Every sentence delivers distinct, valuable information with no filler or tautology.

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, intended usage, error semantics, cost and payment failure modes, and the equivalent HTTP route. The absence of an output schema is acceptable because the first sentence makes clear that the tool returns current Coinbase prices in USD, and the annotations cover safety characteristics.

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 schema already fully documents the optional `symbols` parameter with a default and example, so baseline is 3. The description adds meaningful extra constraints: 'up to ten crypto assets' and the per-symbol error behavior for unavailable assets, which help the agent set expectations beyond 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 opens with a specific verb-resource pair: 'Coinbase spot price in USD for up to ten crypto assets,' which clearly states what the tool returns and the source. The line 'Use this for a current crypto price' reinforces the purpose and helps distinguish it from related sibling tools like defi_token_prices or 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?

The description explicitly says 'Use this for a current crypto price,' giving clear usage context. However, it does not name sibling alternatives or specify when not to use this tool, stopping 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.