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

Goes well beyond the annotations (destructive/idempotent/openWorld): it discloses the credit cost, the exact failure shape on insufficient balance (returns balance, shortfall and creditsInformationUrl without a checkout), why retries are safe ('durable purchase/job reconciliation ... including after expiry'), and explicitly scopes out video authorization and planning-model calls.

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?

Front-loaded with the money-spending action and no filler sentences, but the chat-mode field list is a dense run of identifiers and the legacy-token plus 'no video authorization' clauses stack up, making it heavier to parse than it needs to be.

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, credit-spending operation it covers cost, preconditions, error path, retry semantics and deprecation, and an output schema exists so return values need no restating. Nothing an agent needs before invoking it is missing.

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 coverage is 100%, so the per-parameter detail is already carried by the schema (baseline 3). The description adds group-level integrity semantics the schema does not state: the quote identifies itself only if projectId, revisionId, mode, operationId, quoteToken, modelId, priceVersion and quotedCredits are passed unchanged, and it flags confirmationToken as a legacy path.

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?

Names a specific verb and resource — spends credits for the approved quoted pictures — and its wording ('exactly the approved quoted pictures', 'the quote's unchanged ... fields') makes clear it is the commit step that follows studio_storyboard_stills_quote, not the quoting step itself.

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?

Gives a clear precondition chain: the quote must exist and the listed fields must be unchanged, with chat vs legacy confirmationToken paths spelled out. It stops short of naming 'call studio_storyboard_stills_quote first' as an explicit alternative, so the routing is implied rather than stated.

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