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

Annotations already declare readOnly=false, idempotent=false, openWorld=true and destructive=false, so the safety profile is covered. The description adds genuinely new behavior: the operation is asynchronous (a job), and the output is truncated to at most 15 seconds taken from the start of the clip. It does not mention cost, latency, or whether the source clip is preserved.

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?

Two compact clauses plus an endpoint reference, with the core action and the 15-second truncation front-loaded. No filler or redundant restatement of the title.

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?

With no output schema, the description carries the burden of describing the return, and it does so by indicating a job is produced and that the resulting clip is capped at 15 seconds from the start. It could be more explicit that a job id is returned and must be polled, but the essentials for correct invocation are present.

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 all five parameters are already documented, including the 3-15 second duration bound and the default-inherits-from-source behavior for resolution and aspectRatio. The description's 'up to 15 s of it, from the start' reinforces the duration semantics but adds little beyond the schema, so the baseline 3 applies.

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?

States a specific verb and resource ('Change a generated clip with a prompt') and enumerates the kinds of edits (colours, objects, style). It also distinguishes itself from vids_create_video by noting it is 'A job, like vids_create_video', though it never explicitly contrasts with vids_extend_video or vids_upscale_video.

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?

The phrase 'A job, like vids_create_video' implies the async job pattern and that the caller should poll vids_get_job, and 'from the start' hints at a scope limit. However, there is no explicit when-to-use guidance versus the closely related vids_extend_video or vids_upscale_video siblings, leaving the choice to inference.

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