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

Annotations already declare readOnlyHint=true and openWorldHint=true, so the safety profile is covered. The description adds useful context (pagination, quote-currency conversion) but says nothing about rate limits, freshness window, or what 'new' means, which matters for a live market data tool.

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 sentences, zero waste. The primary purpose is front-loaded and the disambiguation follows immediately, so the agent gets the essential routing information first.

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 an output schema covering return values and annotations covering the safety profile, the description supplies purpose, alternatives, and pagination behavior. The only real gap is not clarifying what qualifies as a 'new' coin, which slightly limits correct invocation.

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 page, limit, and vs_currency are already documented in the schema, including the full allowed-value list. The description only echoes the currency concept ('values quoted in vs_currency') without adding syntax or defaults, so baseline 3 applies.

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 (fetch), resource (CoinGecko's new-cryptocurrencies table), and behavior (paginated rows quoted in vs_currency). It explicitly names the sibling tools it is not (coingecko_markets, coingecko_trending, coingecko_gainers_losers), so an agent can distinguish it without opening any 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?

The second sentence names concrete alternatives and the condition each covers ('broader market', 'rankings'), giving clear routing. It stops short of an explicit 'use this when you want newly listed coins' trigger, so usage is implied rather than fully stated.

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