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

Annotations already declare readOnly=false, idempotent=true, destructive=false, and openWorld=false, so the core safety profile is covered. The description adds that it affects how a clip mixes with lower tracks and returns an edit result, but it does not explain what changes are made to existing state, required permissions, or how the returned edit result should be interpreted beyond pointing to server instructions.

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 two tight sentences, front-loading the blend-mode concept and then mentioning the return result. There is little wasted text, though the first sentence is a concept fragment rather than a direct action statement.

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?

Given an output schema and rich annotations, the description need not explain return values or safety in detail. It supplies the essential blend-mode context and a catalog reference, and the schema covers most parameter mechanics. The main omission is usage guidance, which is scored separately.

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 50%, with timeline_id and preview documented in the schema but clip_id and mode lacking schema descriptions. The description partially compensates for mode by listing example blend modes and linking to a catalog, but it says nothing about clip_id and does not clarify preview behavior beyond the 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 identifies the resource and setting: a video clip's blend mode that controls how it mixes with tracks below. It enumerates representative modes and points to a catalog, making the tool distinguishable from sibling clip setters. It is slightly oblique by describing the setting conceptually rather than explicitly saying 'sets the blend mode of clip_id', but the purpose is still clear.

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?

There is no explicit guidance on when to use this tool versus alternatives such as clip.set_transform, clip.set_enabled, or clip.set_mask. The blend-mode concept implies it is for visual compositing, but no conditions, prerequisites, or exclusions are stated.

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