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

With readOnlyHint, openWorldHint, and idempotentHint already declared, the description still adds substantial context: per-call pricing ($0.002 via x402 USDC or card key), first 25 calls free, failed calls free, the 24-hour change sourced from Coinbase where available, and a 'changes nothing' statement. It even explains why repeats are not free, which accounts for the non-idempotent hint.

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?

Front-loaded with the resource, supported inputs, and limits before the pricing and usage details. Dense but nearly every clause carries information; the pricing/credit sentence is the only slightly tangential element, though it is operationally relevant.

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?

No output schema exists, so the description must indicate what comes back, and it does: current price in each requested currency plus 24-hour change. Combined with input limits, id-source flexibility, and cost expectations, an agent has everything needed to call it 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?

Schema coverage is 100%, so the baseline is 3, but the description goes further by naming valid CoinGecko id examples (bitcoin, ethereum, solana, usd-coin), noting that tickers such as BTC also work, and stating the 25-id and 5-currency caps. These details add meaning beyond the terse schema strings.

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 ('Current price of up to 25 cryptocurrencies by CoinGecko id ... in up to 5 currencies') with concrete id examples. The clause 'Use to price coins that are not on-chain tokens' implicitly separates it from siblings like token_price and price_token, so an agent can route correctly without opening the 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?

Gives three concrete use cases: pricing non-on-chain coins, valuing a portfolio in several currencies, and checking a move. It also warns that repeat calls are charged. It doesn't name a sibling to use instead for on-chain tokens, so the exclusion is implicit rather than an explicit alternative.

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