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

Annotations already establish read-only, non-destructive, open-world behavior, and the description adds important operational context: minute-level refresh, per-call cost, x402/USDC payment, and that failed calls are not charged. It stops short of explaining payment setup or rate limits, but adds substantial value beyond the 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?

Two tight sentences front-load the data scope and then the cost/payment behavior. There is no redundant or filler text.

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 tool with no output schema, the description covers what data is returned, refresh cadence, universe size, cost, payment rail, and billing failure policy. An agent has enough information to call it and understand the charge implications.

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 single optional tokens parameter is fully documented in the schema, including comma-separated syntax and the empty-means-top-50 default. The description reinforces the top-50 scope but adds no parameter detail beyond the schema, so the baseline of 3 is appropriate.

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 states a specific resource and scope: live prices for the top 50 crypto coins, with change intervals and volume. It is clearly a market-data read tool, though it does not explicitly name or distinguish itself from the sibling prices_free tool.

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 paid cost is stated, which implies this is the paid alternative to a free tool, but the description never explicitly says when to use this versus prices_free or other siblings. Usage is inferable from the pricing model rather than directly guided.

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