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

Annotations already declare destructiveHint=true, idempotentHint=true, and readOnlyHint=false. The description adds value on top: it warns that existing timeline state is changed and that the call returns a retry-safe receipt, which clarifies the retry semantics of the idempotency contract. It stops short of saying exactly what is destroyed or how the deltas behave.

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 with no filler, and the mutation/state-change fact is placed early. Slightly under-elaborated rather than padded, which is preferable, though it could have spent one more clause on the delta parameters.

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?

An output schema exists, so return-value explanation is unnecessary, and annotations carry the safety profile. But for a 7-parameter destructive mutation with 29% schema coverage, the description leaves the delta and snap semantics undocumented, which is a real gap 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 description coverage is only 29% (essentially just projectId and expectedRevision). The description mentions the revision concept but says nothing about trimStartDeltaSeconds/trimEndDeltaSeconds units or sign conventions, snapToFrame, or idempotencyKey, so the low-coverage gap is not compensated.

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 pair ("trim or extend") on a specific resource ("one timeline item") with the revision constraint. It is clear what the tool does, but it never names the obvious sibling timeline_trim_preview, so an agent must infer the apply-vs-preview split from the names alone.

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?

"Changes existing timeline state" implies this is the committing counterpart to the preview tool, giving implied context for use. However, there is no explicit when-to-use, no reference to timeline_trim_preview, and no stated prerequisites beyond the revision, so the routing guidance is only inferred.

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