render_overlay

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

Annotations only declare readOnlyHint=false, openWorldHint=true, destructiveHint=false. The description adds meaningful context beyond that: async job semantics (returns job_id), a hard dependency on the user's FFmpeg, and auth/tier gating. It doesn't cover failure modes or output location behavior.

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?

Front-loaded with the purpose and return value, then format behavior, then prerequisites, then the follow-up action. Dense and every clause is actionable; no filler.

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 correctly summarizes the return (job_id) and the polling pattern. Combined with format semantics and auth prerequisites, an agent has enough to invoke it, though async completion details and output_dir defaulting are left implicit.

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 only 33% and output_dir has no schema description, so the description carries weight. It explains the format enum well (MP4=green screen, MOV=transparent ProRes 4444, WebM=transparent VP9), which the bare enum cannot convey; output_dir remains unexplained but is largely self-evident.

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?

Specific verb+resource: 'Start a local animated overlay render and return job_id'. It also distinguishes itself from configure_overlay by noting the configuration comes from configure_overlay, and from job_status by naming it as the polling follow-up.

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 real preconditions (needs the user's FFmpeg, free configurations need no login, others need Pro) and the correct next step ('Poll job_status for the file'). It stops short of explicitly stating when to use this versus add_overlay_to_video or edit_video.

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