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

Annotations already declare readOnlyHint=true and openWorldHint=false, so safety is covered. The description adds valuable behavior beyond that: the data is delayed ~30 minutes and free versus paid, which tells the agent when this data is or isn't fresh enough. It stops short of any rate-limit or refresh-cadence detail.

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?

Three short sentences, zero filler, with the most decision-relevant fact (FREE) front-loaded. The alternative and its price are packed into the final clause without redundancy.

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 no output schema, the description carries the return-value burden and does so by listing price, market cap and 24h change. Combined with the freshness caveat and the routing to lookup_coin, an agent has everything needed to decide and call correctly.

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 takes zero parameters, so per the baseline there are no parameter semantics to document. The description usefully confirms the zero-argument nature by implying a fixed top-10 scope, though it adds nothing more about invocation.

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?

States a specific verb and resource (snapshot of the top 10 coins) plus the exact fields returned (price, market cap, 24h change), and explicitly contrasts with the sibling lookup_coin for broader coverage. An agent can distinguish it from lookup_coin without opening either schema.

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?

Names the alternative (lookup_coin) and the exact condition that selects it: any of 500 coins with more fields, at $0.002. It also signals this is the free tier, giving a clear cost-based reason to prefer it for the top-10 case.

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