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

Annotations only indicate non-readonly, non-destructive, non-idempotent behavior; the description adds essential details: it consumes the weekly free video limit, spends account credits, may be slower than generation, returns a job_id for polling, and reports 4K plan locks as clean errors. This fully compensates for the sparse annotations.

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?

Longer than average, but every block earns its place: purpose, usage constraints, per-parameter guidance, async behavior, and return shape are all addressed. The opening sentence says exactly what the tool does, and the parameter paragraphs are logically organized.

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 mutation tool with no output schema and zero schema coverage, this description is fully sufficient: required inputs, parameter semantics, error behavior, polling path, quota impact, and expected response structure are all covered. Nothing an agent needs to invoke it correctly is missing.

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 0%, but the description compensates exceptionally well. It explains account must come verbatim from account_used, why using another account errors, gives the exact allowed resolutions for target_resolution, notes the default and paid-tier caveat, and makes media_id's origin clear via the 'from a prior generate_video call' context.

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: 'Upscale an existing generated video' from a prior generate_video call to a higher resolution. It clearly distinguishes this from sibling operations like edit_video and extend_video by anchoring it to the output of generate_video and the download resolution options.

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?

Provides clear context: this is for a video produced by generate_video, uses the account from the prior result, and should be polled via check_job if it takes longer than ~40s. It does not explicitly name alternatives like upscale_image, but the lineage requirement makes the intended usage unambiguous.

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