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

Annotations only declare readOnlyHint=false and openWorldHint=true, so the description carries most of the load and does it well: it discloses pricing ($0.01/sec, min $0.05, max $0.30), asynchronous execution, and that the call returns a generation_id rather than a result. What's missing is any hint about processing time or input-duration limits tied to that pricing cap.

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?

Three short sentences, front-loaded with the verb and resource, then cost, then the async contract. Every sentence carries information the agent needs and none is wasted.

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 correctly supplies the return contract (generation_id plus the get_generation polling loop), and it adds cost. For a one-parameter tool this is close to complete; only expected turnaround or maximum input length is absent.

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% for the single 'video' parameter, including URL/base64 format, so the schema already does the work. The description adds only the implicit constraint that the input should be black-and-white footage ('old videos'); it repeats no parameter detail, which is appropriate at this coverage level.

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 ('Colorize old videos'), which is unambiguous and implicitly distinguishes it from the photo counterpart ai_photo_colorizer by naming video as the medium. It does not explicitly name the disambiguation, but an agent can route correctly from the resource noun alone.

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?

Usage here is about workflow rather than alternatives: it tells the agent this is async and to poll get_generation until status is 'completed', which is genuinely useful routing. However, there is no guidance on when NOT to use it (e.g., instead of ai_video_restyle or ai_video_upscaler for non-colorization needs).

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