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 only 'normalized' as extra behavioral context and says nothing about rate limits, data freshness, or auth. Useful but thin given annotations carry most of the load.

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 with zero waste: purpose first, alternative routing second. Everything is front-loaded and each sentence 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?

With an output schema present the description need not explain return values, and with zero params there are no inputs to document. It covers purpose, source, and the sibling alternative, which is complete for a no-arg read tool, though it could note what 'global metrics' concretely includes.

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?

The tool takes zero parameters, so there is nothing for the description to clarify and the baseline of 4 applies. No parameter semantics issues exist.

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 ('Returns normalized global market metrics') and scopes it to CoinGecko's public charts page. It also names the sibling coingecko_global_charts to disambiguate, which is what pushes it above a plain 3, though the overlap in both mentioning 'charts' keeps the boundary slightly fuzzy.

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 routes the agent explicitly: use coingecko_global_charts for global chart series, implying this tool is for the metrics snapshot. It names the alternative but never states affirmatively when to prefer this tool or any exclusions, so it stops 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.