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

Annotations already declare readOnlyHint, idempotentHint, destructiveHint=false and openWorldHint=false, so the safety profile is fully covered without the description. The description's only added behavioral signal is "free," which conveys a cost implication not present in the structured fields; it says nothing about rate limits, ordering, or completeness of the list. That is a modest but real addition over the annotations.

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?

A single front-loaded sentence with no filler, and the verb-resource core comes first. The "read-only" clause mostly restates readOnlyHint and is slight redundancy, but it costs almost nothing.

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 trivial zero-parameter lookup the description is close to sufficient, and the annotations carry the safety profile. However, with no output schema present, the description does not indicate what the list contains (model IDs, task types, pricing tiers), which is exactly the information an agent needs to decide whether this tool answers its question.

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 no parameter semantics to explain and the description is not expected to compensate. Baseline for a parameterless tool applies.

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?

"List supported Workers AI reference models" is a specific verb plus a well-scoped resource, and the parenthetical narrows scope to free/read-only models. It does not name or contrast with any sibling, but the siblings listed (audit, bill_check, quick_check, report) are functionally distinct enough that confusion is unlikely.

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?

There is no explicit when-to-use or when-not-to-use guidance, and no mention of alternatives for model discovery versus running a check. The parenthetical "free" hints that this is a no-cost discovery call, but the agent must infer that on its own.

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