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

Annotations already declare readOnly/openWorld/idempotent/non-destructive, so the safety profile is covered. The description still adds real behavioral context: no auth required ('Keyless'), the failure mode for unsupported commodities (found:false with a pointer), and the implicit ordering (rows sorted by current reserves, descending), which governs how the limit truncates results. It stops short of disclosing pagination or exact result-shape details.

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?

Front-loaded with the core purpose before coverage caveats, examples, filter, sort, and auth. Dense with parentheticals and em-dashes, but each clause carries distinct information (coverage gap, fallback target, filter syntax, ordering, keyless) rather than filler.

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 no output schema, the description carries the return-shape burden and does so: prior-year actual + current-year estimate production plus reserves, per country, for one commodity. Coverage limits, failure behavior, auth, and ordering are all present, so an agent can call it correctly without additional context.

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 the schema already documents commodity, countries, and limit, giving a baseline of 3. The description adds meaning beyond it by noting that countries accepts a comma-separated string OR array and that rows are otherwise sorted by current reserves descending — useful context for interpreting the limit parameter.

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+resource with scope: 'World mine/plant PRODUCTION ... and RESERVES, by country, for one mineral commodity from the USGS Mineral Commodity Summaries.' It explicitly names the sibling it falls back to (mcs_commodity_data) for the 10 uncovered commodities, so an agent can distinguish it from mcs_commodity_data and mcs_list_commodities without opening a 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?

Gives concrete when-to-use phrasing ('which countries hold lithium reserves', 'China vs. Australia rare-earth production') and an explicit when-not boundary (75 of 85 commodities; scrap/slag/crushed-stone return found:false and point to mcs_commodity_data instead). Alternatives and the condition that selects them are stated, not inferred.

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