List Codex models (free)

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

Annotations already declare readOnlyHint=true, but the description adds significant behavioral context: reads from cache with fallback, 'source' field indicates provenance, fallback lacks effort data, and backend validation may reject listed values or accept unlisted ones. It also notes the payload is the same as a resource, going far beyond the 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?

Each sentence adds a distinct piece of information: purpose, cost, source, validation caveats, payload equivalence, and caching instability. The description is front-loaded with the main action and is compact despite the detail.

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 zero-parameter read-only tool with an output schema, the description fully explains what the tool returns, how it obtains data, its reliability, and its relationship to other resources. There are no obvious gaps.

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?

Zero parameters means no schema to elaborate. The description still explains the output meaning (model slugs and reasoning-effort sets) and the source field, which is helpful even though the output schema is present.

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 states a specific verb and resource: 'List Codex model slugs...' with the additional clarification of the reasoning-effort data. It clearly distinguishes this from sibling tools by focusing on model discovery and the 'codex://models resource' equivalence.

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 provides clear context on when to use (advisory discovery) and explicitly warns against certain uses ('do not cache it by the capabilities fingerprint'). It does not name alternative tools explicitly, so it misses the full 'when not / alternatives' bar.

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