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

Annotations already declare readOnlyHint, openWorldHint, idempotentHint, and destructiveHint=false. The description adds valuable behavioral context beyond annotations: the cost per call ($0.001 USDC) and the exact byte-identical API endpoint. It also confirms the inclusion of the exchange's own clock, which is a subtle behavioral detail. 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?

The description is three tight sentences: core data first, cost second, API equivalence third. Every sentence adds distinct information and there is no filler. The front-loaded enumeration of returned fields makes the tool's purpose immediately clear.

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?

With one well-documented parameter, a rich output schema, and annotations covering safety and idempotency, the description provides sufficient context: the data fields, the pricing, the API mapping, and the single-product scope. There are no missing return-value explanations because the output schema exists. Nothing critical is omitted 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 has 100% coverage with a detailed description of the product parameter, including examples and required flag. The description only restates 'one Coinbase product' without adding new parameter semantics. Baseline 3 is appropriate since the schema already carries the full burden.

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 enumerates the data returned: 'Last trade, top of book, 24h volume and the exchange's own clock', and scopes it to 'one Coinbase product'. This clearly distinguishes it from sibling tools like market_cbex_best_quote (which returns only best quote) or market_cbex_clock (which returns only the clock). The API equivalence further pins down its purpose.

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 usage through the enumerated data fields and product scope, but it does not explicitly state when to prefer this tool over alternatives such as market_cbex_trades or market_cbex_stats. There is no when-not guidance or naming of sibling tools that cover different use cases. The API endpoint reference is informative but not a routing guideline.

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