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

Annotations already declare readOnlyHint, openWorldHint, and idempotentHint. The description adds non-redundant context: rate limit ('10 calls/day'), authentication requirement ('no API key needed'), and asset coverage ('any CoinGecko ID'). It also restates the return format, which is somewhat redundant with the output schema but still useful.

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 well-structured and front-loaded with the core purpose. Each sentence contributes meaningful information, including supported assets, use case, return format, and rate limits. It is slightly longer than necessary because the return format duplicates the output schema, but it remains efficient.

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 read-only tool with an output schema, the description covers the essential aspects: what it does, when to use it, rate limits, and authentication. It does not mention error handling or invalid asset behavior, but those are not critical for this tool's typical use. Overall, it is complete enough for an agent to invoke 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 description coverage is 100%, so the baseline is 3. The description does not add significant parameter-level detail beyond what the schema already provides (e.g., formatting, case-insensitivity, legacy flags). It correctly references the query parameter but adds no new semantic information.

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 clearly states 'Live crypto price feed via CoinGecko' and specifies it 'Returns real-time USD price and 24h change for any supported asset.' The verb ('returns') and resource ('crypto price feed') are explicit, and the distinction from siblings like gas station or tx_simulate is obvious.

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?

It gives a direct use case: 'Use before tx_simulate to get current gas cost in USD,' and mentions the free tier limit ('10 calls/day, no API key needed'). It lacks explicit alternatives or when-not-to-use guidance, so it falls short of a 5.

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