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

Annotations already declare readOnlyHint=true, idempotentHint=true, destructiveHint=false, and openWorldHint=true, so the safety and idempotency profile is fully covered for this no-param read. The description adds 'all supported currencies' scope, which is useful, but doesn't explain return structure beyond what annotations and output schema already provide. With annotations carrying the behavioral burden, a 3 is appropriate.

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 core description is a single efficient sentence with the resource front-loaded. It includes a pricing note that isn't strictly part of the tool semantics, adding a bit of noise, but the tool description itself is tight.

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 zero-parameter read-only list tool with an output schema and full annotations, the description covers what the tool returns ('all supported currencies'). An agent has enough to call it. It could note the list's typical use for constructing simple_price queries, but this isn't essential.

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?

Zero parameters, so baseline 4 applies. No parameter semantics needed.

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 ('query all the supported currencies on CoinGecko') with clear scope ('all'). A named endpoint resource ('supported vs currencies') that's distinguishable from sibling list tools like get_coingecko_coins_list.

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?

No guidance on when to use this versus alternatives. The description doesn't explain the relationship to sibling tools like get_coingecko_simple_price or get_coingecko_coins_list, or explain what this list is used for (e.g. as valid currency codes for simple_price).

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