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

readOnlyHint already covers the safety profile, so the description only needs to add what annotations don't. It does add the sort key (input price) and the result shape (one row per model-provider pair), but says nothing about output fields or what happens when the catalogue has ties or sparse data. Adequate, not rich, against an already-declared read-only annotation.

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, front-loaded with the definition and followed immediately by sibling routing. No filler, and the disambiguation clause is the highest-value content placed 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?

For a two-parameter read-only lookup with a fully described schema, the definition covers purpose, granularity, ranking key, and alternatives. Without an output schema, a brief note on returned fields would close the remaining gap, but nothing needed to call it correctly is missing.

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 both limit and the category enum are already fully documented in structured data. The description's phrase 'one model type' echoes the category parameter without adding format or default details beyond what the schema states. Baseline 3 applies when the schema does the heavy lifting.

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 resource and ranking (cheapest current offers, one model at one provider, sorted by input price) and pins the row granularity explicitly. This makes it distinguishable from cheapest_models and cheapest_for_workload 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?

Names two alternatives and the selection condition for each (per-model aggregation, monthly workload), which is strong routing guidance. It does not address the other lookup siblings such as search_offers or get_model_prices, so an agent still has to infer when this beats a broader offer search.

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