replaceTimeline

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

Annotations already declare destructiveHint=true and readOnlyHint=false, but the description adds non-obvious behavior beyond them: intervals are SORTED so reordering is impossible, and the call is refused when it would merge away, shorten or drop an existing clip, with the refusal naming the affected clips and the replacement tool. That is real operational context an agent cannot get from the annotations.

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 action and its effect, then the ordering guarantee, then the exclusions and alternatives. Dense and mostly waste-free, though the phrasing around the two sibling tools is slightly repetitive and could be tightened.

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?

No output schema exists and none is needed for a mutation, but the description does cover the important failure mode (refusal naming clips) and the input semantics. Minor gap: it says nothing about the optional 'reason' parameter or any prerequisite like a checkpoint, which siblings such as createCheckpoint imply may matter.

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 only 33% (projectId documented, reason and intervals structures undocumented). The description compensates substantially for the key parameter by defining what the intervals mean — source-time ranges of the primary asset where everything outside becomes a trim — which the schema does not say. 'reason' remains unexplained, keeping this below a 5.

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+resource ('Replace the whole timeline') plus the exact scope of the input ('kept intervals of the primary asset's source time') and the consequence ('Everything outside the intervals becomes a trim'). It also distinguishes itself from siblings by name, so an agent can pick it over moveClip/insertClip without opening a schema.

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?

Explicit when-to-use ('ONLY when the user explicitly asks you to rebuild the timeline from scratch'), when-not ('DO NOT use this for cut silences or remove pauses'), and two named alternatives with their triggering conditions (moveClip for reordering, insertClip for other assets). This is a complete routing instruction set.

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