session_create

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

Annotations only state readOnlyHint=false, so the description carries the burden of explaining the mutation. It adds meaningful context: the created record is a plain UUID, not a provider-native session, and does not satisfy Codex resume. This goes beyond the schema, though it does not disclose return values or side effects like setAsActive.

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 with no filler: the first states the core operation, the second delivers the critical caveat. Every sentence earns its place and the key limitation is front-loaded near the main purpose.

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 simple create operation with full schema coverage and basic annotations, the description is mostly complete and includes the essential caveat about provider-native sessions. It does not explicitly state the return value or that setAsActive defaults to true, which would be useful given there is no output schema, but these are minor 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?

Schema description coverage is 100%, with each parameter (cli, description, setAsActive) already documented in the input schema. The description adds no additional parameter-level meaning, so the baseline score of 3 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?

Description specifies a concrete action ('Create') on a specific resource ('gateway session record') and clearly distinguishes it from provider-native sessions via the plain-UUID note. This differentiates it from sibling tools like codex_fork_session and codex_request without needing to inspect schemas.

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 warning that Codex resume needs a real Codex UUID provides an explicit when-not-to-use condition, and the 'gateway bookkeeping' phrasing clarifies the tool's narrow role. However, it does not name an alternative tool to use instead, leaving the agent to infer from sibling names.

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