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

Annotations already declare readOnlyHint, idempotentHint, and non-destructive behavior. The description adds valuable context: the call is a single bundled request, sourced from CoinGecko, and costs $0.50 USDC via x402 on Base, which are important operational details not present in 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 efficient and front-loaded with the primary action. It includes an explicit usage pointer and source/pricing details in a compact form. However, it could be slightly more concise by merging the source and price sentences, but it remains readable.

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?

Given the output schema exists and annotations cover safety, the description provides all necessary selection context: what data it returns, when to use it, the data source, and cost. The sibling tools are different domains, and the description names the specific alternative (get_crypto_price), making the choice clear.

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 tool has zero parameters, so the schema already fully covers inputs (schema coverage 100%). The description adds meaning by describing what data will be returned (price, 24h/7d change, market cap, volume) and the coin list, which is useful given no parameters.

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 starts with 'Returns the top 20 cryptocurrencies by market cap in one call' which names a specific verb, resource, and scope. It also lists the exact data fields (price, 24h change, 7d change, market cap, volume) which distinguishes it from sibling tools like get_crypto_price and other bundles.

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?

Explicitly says 'Use this instead of individual get_crypto_price calls when you need broad market coverage.' This provides a clear when-to-use and names the alternative, making it easy for an agent to choose this tool over get_crypto_price.

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