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

Annotations already declare readOnlyHint and openWorldHint, so the safety profile is covered. The description adds genuinely non-obvious context: the paid x402 model at $0.003 USDC per call, plus hard ceilings of 50 coins and 10 currencies. It stops short of return/pagination details, but the cost disclosure is the important behavioral fact here.

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 tightly packed sentences, front-loaded with what the tool returns, then how to call it, then the cost. No filler and no redundancy with the schema.

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 compensates by naming the returned fields and the billing model. It is essentially complete for a two-parameter read tool, with only minor gaps around failure modes and whether symbol ids are case-sensitive.

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 is 100%, so baseline is 3, but the description goes beyond the schema by supplying accepted symbol formats (btc, eth, sol), alternative CoinGecko ids, example currencies (usd, cad, eur) and per-call limits — none of which appear in the schema's terse property descriptions.

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+resource ('Live crypto prices') and enumerates the returned fields (24h change, market cap), which is more than a restatement of the name. It does not, however, distinguish itself from close siblings such as token_price, crypto_movers, or crypto_candles, so an agent must infer the boundary itself.

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 explains how to invoke it ('Pass symbols (btc,eth,sol) or CoinGecko ids') but gives no when-to-use/when-not guidance and never names an alternative such as crypto_candles for historical data or crypto_movers for rankings. Usage is implied by the resource, not by any routing rule.

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