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

Goes well beyond the annotations: it discloses the conflict-resolution rule (better quality score wins per frame), the seam-blending behavior that prevents corner jumps, and that otherTrackId is removed. The one unresolved point is reversibility -- it does not say whether a merge can be undone, which matters given idempotentHint=false and the removal of a track (mild tension with destructiveHint=false).

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?

The core action is front-loaded in the first clause and every sentence carries operational content. The prose is dense and long-sentenced, and the return-value details plus the preview recommendation could be ordered more crisply, but nothing is padding.

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?

With no output schema, the description usefully summarizes the response (where the merged result still references the removed track, the new quality verdict and flagged ranges) and points at preview_range for visual confirmation. What it omits is failure modes and undo behavior for a non-idempotent mutation.

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 3 is the baseline, but the description earns more by explaining the purpose behind blendFrames ('a few frames are blended so the corners do not jump') and clarifying that trackId is the survivor the merged track is written under. It stops short of restating the 0-12 range, which the schema already covers.

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 ('Join two object tracks of the same asset into one, under trackId') with a concrete example use case (two tracks of one sign seeded at different times). It is unmistakably distinct from neighboring tools like split_track, edit_track and smooth_track.

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 clear precondition ('Both must be plane tracks or both box tracks') and a recommended verification step ('a preview_range call with overlays ["tracks"] ... run it to check'), plus the 'Free' cost signal. It does not, however, say when to prefer split/merge alternatives or what to do when the precondition fails.

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