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 one genuine behavioral detail (results are deduplicated) and reveals that output spans two sections (coins and categories), but says nothing about rate limits, caching, or freshness of "trending" data.

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 filler, with the core purpose front-loaded before the routing sentence. Every clause earns its place.

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?

An output schema exists, so return values need no explanation, and the 100% schema coverage handles both parameters. Between the purpose statement and the sibling routing, an agent has everything needed to select and invoke this tool 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 both parameters (limit, vs_currency) are already fully documented by the schema. The description's phrase "for a quote currency" loosely maps to vs_currency but adds no format or constraint information beyond the schema.

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") and resource ("trending coin and category highlights") plus a scoping qualifier ("deduplicated") and the required quote-currency frame. It is immediately distinguishable from siblings like coingecko_gainers_losers and coingecko_new_coins 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?

Second sentence explicitly names three alternative tools and the condition that selects each: market movers, recent listings, and category browsing. This is exactly the when-to-use-something-else guidance the dimension rewards.

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