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

Annotations already declare readOnly/idempotent/non-destructive, so the remaining burden is low, and the description adds genuinely new behavior: the card renders on its own with progress, then plays, plus a download per format. It also removes an expected precondition by stating wait_for_video is unnecessary. Minor gap: nothing about what happens with an invalid or still-queued id.

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?

One front-loaded sentence led by the verb, with the post-create nuance and the fallback trigger appended rather than buried. No redundant restatement of the title or the schema.

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 the description compensates by explaining what the caller gets back (a player card with render progress and per-format downloads). For a one-parameter read-only display tool that is close to sufficient; only error/edge behavior is left unstated.

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% and the single parameter's constraint (1-8 items) is fully documented there, so the baseline applies. The description adds that the ids come from the create_* tools' return values, which is useful provenance but not additional format or semantics beyond the schema.

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 ("Shows videos as players") and describes what that actually means: a live render with progress, then playback with per-format downloads. It implicitly separates itself from get_video/list_videos by describing a player surface rather than data retrieval, though it never names those siblings explicitly.

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 explicit trigger conditions: immediately after create_lyric_video, create_canvas, or create_music_video using the returned ids, or whenever the person asks to see a video. It also names the alternative it supersedes ("no need to wait_for_video then"), which is exactly the routing decision an agent needs.

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