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

Annotations already provide idempotentHint=true and destructiveHint=false. The description adds that spans REPLACES the existing list, spans=[] turns captions back on, and that audio and cut are untouched. It also clarifies project-scoping. These details go beyond annotations and accurately describe behavior without contradiction.

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?

The description is somewhat long but every sentence contributes necessary context (scope, replace behavior, when not needed). It front-loads project-scoping and then explains the mechanism. No filler or repetition, though it could be tightened slightly without losing information.

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 mutation tool with no output schema, the description covers the core behavior (hiding windows), the parameter semantics, the replace-all behavior, the reset case, the non-destructive nature, and the scope. It even mentions return (project identity) and exclusions. Nothing an agent needs to call it correctly 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 only 50% (project_id has a description, spans does not). The description fully compensates for spans by specifying the format [[start, end], ...] in program seconds, the replace semantics, and the empty-list behavior. Project_id's schema description is also reinforced. This adds significant meaning beyond the bare schema.

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 clearly states the action (hide burned captions), the target (over specific program-time windows), and the effect (leaving them on elsewhere). It distinguishes from siblings like set_caption_style and set_caption_fixes by focusing on muting windows, not styling or fixing captions. The verb 'hide' and resource 'captions' are specific.

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 explicitly says when to use: when a full-frame effect, graphic, or text treatment would have captions burned across it. It also excludes inserted media and title cards as they are never captioned. However, it does not name alternative tools or conditions that would select them, though the exclusions and context are clear enough for an agent to decide.

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