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

Annotations already declare readOnly, idempotent, non-destructive and closed-world, so the safety profile is fully covered. The description adds the scope of the comparison (clips, tracks, settings) but says nothing about directionality from→to, ordering of results, or how large diffs are represented.

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?

A single tight fragment with no filler. It would be marginally stronger if it led with a verb, but every word 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?

An output schema exists, so return values need no explanation, and annotations cover the safety profile. Still, for a diff tool the description leaves the comparison semantics (direction, what counts as a 'settings' difference) implicit, which is the minimum viable rather than complete.

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%: both from and to are documented with the tl_<32 hex> pattern and the note that every edit yields a new handle. The description's "between two timelines" implies the pairing but adds no syntax or ordering semantics beyond the schema, so 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 the resource pair (two timelines) and the exact output dimension (clips, tracks, settings that differ), which cleanly separates it from timeline.get and timeline.history. It is a sentence fragment with no explicit verb, but the meaning is unambiguous.

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?

There is no statement of when to use this versus timeline.get, timeline.history, or edit.batch. An agent must infer the comparison scenario entirely from the one-line description.

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