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

With readOnlyHint=true in annotations, the description adds valuable behavioral context beyond that: it specifies the input format (comma-separated symbols, max 50), the output structure (prices, missing, source, age_secs), and the 'canonical' nature of the prices. It does not contradict any annotations and enriches the agent's understanding of what to expect.

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 compact and front-loaded: it states the primary purpose in the first clause, then provides param and return details in just two more sentences. Every piece adds value, and the return structure is especially useful given the absence of an output schema. The '[TRUTH ANCHOR]' prefix is minor noise but does not detract from conciseness.

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 tool with one parameter and no output schema, the description provides all necessary context: it explains the input format, the maximum batch size, and the exact JSON return shape including a 'missing' array for coin resolution. This makes the tool self-contained without requiring the agent to infer behavior.

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 coverage for the only parameter 'coins' is 0%, but the description fully compensates by explaining the format: 'comma-separated symbols, e.g. 'BTC,ETH,SOL' (max 50).' This gives the agent explicit syntax, an example, and a constraint that the schema alone lacks. This is exactly the compensation needed for low coverage.

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 clearly states the tool's function: 'Batch canonical prices for several coins in one call.' This specifies a distinct resource (prices) and the batching behavior, distinguishing it from the sibling tool get_price. The mention of 'several coins' reinforces the batch scope, making the purpose unambiguous.

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 for multi-coin queries via 'Batch ... in one call,' which clearly indicates the tool is for when you need several prices. However, it does not explicitly name get_price as an alternative for single-coin requests, so the guidance is clear context without explicit exclusions. This earns a 4 rather than a 5.

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