Add a chapter marker at a timecode

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

Annotations already declare readOnly=false, openWorld=true, idempotent=false, and destructive=false, so the mutation profile is covered. The description adds real behavioral context beyond that: Vimeo rejects two chapters sharing a second, which is an error condition an agent must avoid. It omits auth requirements, return shape, and per-video chapter limits.

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 sentences, zero filler, and the core action is front-loaded before the edge-case constraint. Every sentence carries information an agent needs.

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 three-parameter mutation tool with full schema coverage, no nested objects, and annotations covering the safety profile, the definition is nearly sufficient; the duplicate-second gotcha is the highest-value addition. It does not describe what is returned or confirm scope (single video), but no output schema exists to carry that.

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 all three parameters are already documented, setting a baseline of 3. The description adds meaning beyond the schema for timecode_seconds by explaining that timecodes must be distinct across a generated set, which is a constraint the schema does not express.

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 states a specific verb and resource ('Add a chapter marker') plus the anchoring parameter ('at a timecode'), which naturally separates it from the sibling list_chapters, update_chapter, and delete_chapter. It does not explicitly name those siblings, so it stops short of full differentiation.

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 supplies a usage scenario ('when generating a set from a transcript') and a constraint on that scenario, but never states when to prefer this over update_chapter or how it relates to the existing chapter list. Usage is implied rather than routing the agent between alternatives.

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