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

Annotations already declare destructiveHint=true, openWorldHint=true and non-readOnly, and the description adds genuinely useful behavior beyond them: this spends tokens, requires an explicit user go-ahead naming the purchase, and refunds the unused deposit. It omits what a reservation guarantees, how long it holds, and what happens if the run is never executed. Minor tension only: an `idempotency_key` retry path is described while idempotentHint is false, though key-based retry is not strictly the same claim.

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?

It is short and every clause is load-bearing, but the telegraphic backtick-heavy style and sentence fragments ('The deposit `sandbox_exec` draws on, the unused part refunded') push decoding cost onto the agent. The spending-safety requirement, which is the most important instruction, is not front-loaded.

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, token-spending reservation tool with 5 parameters and no output schema, the description covers pricing, approval and refund mechanics but leaves the agent without the outcome: whether a run ticket or run id is returned, how a reservation is later consumed or released, and whether it expires. Those gaps matter for a purchase-like action.

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%, so the schema already defines `estimate_only`, `run_ticket`, `idempotency_key` and the `video_seconds` bounds, making 3 the baseline. The description adds value mainly by tying `estimate_only` into the price-then-approve workflow, but it repeats the schema on idempotency and says nothing extra about `episodes` or `run_ticket` construction.

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 name and title carry the verb+resource ('Reserve an Explainer Studio run'), and the description reinforces it by describing the token deposit that `sandbox_exec` later draws on, with the unused portion refunded. The first sentence is a fragment that never states the action directly, so the agent must assemble purpose from title plus deposit mechanics, but the intent (hold paid capacity before a studio generation) is recoverable.

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?

It gives an explicit procedural path: price with `estimate_only: true`, quote the price in the same message as the ask, wait for a go naming THIS purchase, and consult `get_recipe` `spending-rules`. That is strong when-to-use and precondition guidance. It stops short of naming when NOT to use it or pointing to a sibling such as `get_studio_run` for checking an existing reservation.

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