Compare models

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

With no annotations, the description carries the behavioral burden, and it adds meaningful details: id resolution rules ('bare model ids when unambiguous') and deduplication behavior ('Ids resolving to the same model are compared once'). It does not describe the output format or explicitly state that this is a read-only operation, but the comparison semantics are clear enough for a tool of this simplicity.

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 tight sentences with no filler. The core purpose is front-loaded, and the second sentence efficiently handles edge cases around id formatting and deduplication. 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?

For a one-parameter tool with no output schema, the description covers the essential usage details: accepted inputs, count limits, and duplicate handling. The main gap is the lack of a brief mention of what the returned comparison looks like, but 'diff side by side' already strongly implies a comparative output.

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 the array shape and requirement. The description adds value beyond the schema by explaining two resolution behaviors: bare ids are accepted when unambiguous, and duplicate model ids are compared only once. This makes the semantics of the ids parameter materially clearer.

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?

The description opens with a specific verb, 'Diff', and a precise resource scope: '2-6 models side by side' on defined dimensions like pricing, context window, and capabilities. This clearly differentiates compare_models from single-model tools like get_model and broad catalog tools like top_models.

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 description gives clear context for when to use the tool: whenever an agent needs to compare multiple models side by side. It also provides important input-usage guidance about provider-prefixed ids and bare ids. However, it does not explicitly name alternatives or state when not to use it versus find_models or get_model.

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