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

Annotations already declare the safety profile (not read-only, open-world, not idempotent, non-destructive). The description adds real value with the source-video mutual-exclusion rule and its error behavior, but says nothing about the asynchronous job/webhook delivery implied by callback_id and the get_work_status siblings, nor about what is produced.

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?

Four tight lines, front-loaded with the operation, then the model restriction, then the source rule and the duration semantics. No filler; each sentence carries a distinct constraint.

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?

For a 9-parameter async video tool with no output schema and no required parameters, the definition covers the critical input rules but omits return/delivery behavior (polling vs webhook via callback_id) and several optional parameters. Adequate to call correctly, not 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 description coverage is only 33%, so the description must compensate, and it does explain the workspace_id/video_url exclusivity, the incremental meaning of duration, and the model restriction. But ratio, prompt, callback_id, and idempotency_key remain unexplained in both the schema and the description.

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 plus scope: video extension by appending N seconds at the end of a source video. That is clearly distinct from video_generate (new video) or video_edit (modify existing), though no sibling is named 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 useful preconditions — only the seedance-2.0 base, and the either/or rule for workspace_id vs video_url with both/neither being an error. However it never says when to choose this tool over alternatives such as video_generate or video_edit, so routing is left to inference.

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