addSpeed

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

Annotations already declare this is a non-destructive, non-read-only mutation. The description adds range semantics (virtual seconds) and the speed multiplier direction, which is useful context beyond the annotations. It doesn't address what happens to overlapping regions or the return value, so with annotations carrying the safety profile, a 3 is appropriate.

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 tight sentences front-load the action and scope, then add the multiplier semantics and the use case. Every clause earns its place.

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 4-param mutation with a 25%-covered schema and no output schema, the description supplies the critical speed semantics and the timeline scope. It could say more about region boundaries or the omitted projectId fallback, but it's largely complete for correct invocation.

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 25% (only projectId is described), so the description must compensate. It successfully explains the speed parameter's semantics (direction, range, clamp values, default), which is exactly the missing meaning. startSec/endSec are half-explained via 'span of the edited timeline (virtual seconds)', but projectId is left to the schema description.

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 ('Add a speed-change region over a span of the edited timeline') and defines scope in virtual seconds. Clearly distinguishable from siblings like setSpeed and addTrim.

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?

Gives a concrete use case ('speed through slow stretches without cutting them'), which implies when to reach for this over setSpeed (region vs. whole clip). It doesn't explicitly name the alternative or state when not to use it, so it falls short of a 5.

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