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

Annotations already declare idempotentHint=true and destructiveHint=true, so the description's repetition of idempotency is partly redundant. It earns credit for adding real context beyond the annotations: exact-version binding, credential handling via argument or Authorization header, and the guarantee that credentials never appear in URLs or error output.

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?

Three sentences, each front-loaded with its main point: the action, the credential path, then the security guarantee. Dense but no filler; the credential sentence is arguably tangential to invocation but carries genuine security value.

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 destructive, non-read-only mutation with no output schema, 8 parameters, and 13% schema coverage, the description is too thin. It omits any explanation of the required fields, the meaning of ready_to_act, or what a session returns, leaving an agent under-equipped to call it correctly.

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 only 13% across 8 parameters, so the description carries the burden of explaining them and largely fails. It addresses only the credential parameter; the four required inputs (slug, accepted_version_id, ready_to_act, idempotency_key) are never explained, and the const:true / idempotency-format constraints are left undocumented.

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 verb (Create) and resource (session) with meaningful qualifiers (idempotent, exact-version) that distinguish it from a generic session starter. However, the phrase 'exact-version session' and 'action loop' are jargon that assumes platform familiarity, and no sibling is explicitly named, so an agent must infer its relationship to prepare_play on its own.

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?

'only after you prepare your own action loop' implies a prerequisite and ordering relative to the prepare_play sibling, which is useful sequencing guidance. But it never names prepare_play explicitly, gives no explicit when-not conditions, and doesn't clarify how it relates to play_status/play_state once a session exists.

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