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

Annotations declare the safety profile (readOnly=false, destructive=false, idempotent=false, openWorld=true), and the description adds real value on top: 'Charged on success only; failed runs are free', the 24h signed URL return, and the publishAs overwrite semantics ('Re-running with the same publishAs key overwrites'). This is the kind of billing/idempotency nuance annotations cannot express.

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 core purpose, then structured segment modes, then return/usage/cost notes. Dense but every sentence earns its place with no filler.

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 3-parameter generative tool with a full output schema, the description covers the segment semantics, the return value (signed URL), cost behavior, and publish routing. An agent has everything needed to invoke 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 coverage is 100%, so the baseline is 3, but the description adds genuine meaning by defining the three valid segment compositions (videoUrl+narrationText, narrationText only, videoUrl+audioUrl) and the title-card/wall-sized behavior. It doesn't restate per-parameter formats, which the schema handles.

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 first sentence states a specific verb (stitches) and output (single MP4 published to Spaces), and the three segment modes (a/b/c) describe exactly what the tool does. This clearly distinguishes it from siblings like quote_demo_video and synthesize_voiceover, which sound adjacent.

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 concrete situations to use it ('marketplace catalog submissions, tutorial videos, or any time you'd otherwise screen-record + iMovie by hand'), which is strong contextual guidance. However it never names the alternative sibling (e.g. quote_demo_video for pricing first) nor states explicit exclusions.

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