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

Goes beyond the annotations by disclosing the cost model ($0.01 USDC via x402) and the return format (data URLs), and the schema explains the payment challenge flow when the signature is omitted. Missing details on output size/volume (14 variants returned at once) and any rate or payload limits keep it from a 5.

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 with the paid precondition front-loaded and zero filler; every clause conveys new information (cost, transformation, ratios, return type).

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 five-parameter, nested-object tool with no output schema, the definition covers cost, transformation, ratios, and return type, and the schema fills in payment and input details. It stops short of describing the shape of the returned data-URL collection or behavior when only some platforms fail.

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 already 80%, so it clears the baseline, and the description adds real meaning by explaining that focus drives focal-point cropping rather than being an abstract x/y coordinate. It does not add anything about format conversion or the payment_signature semantics beyond what the schema states.

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 transformation (one image → every platform's exact ratio and pixel size) and enumerates the ratios produced (16:9, 4:5, 1:1, 9:16, 2:3, 4:3) plus the return form (data URLs). This is enough to distinguish it from omnipost_platform_specs (which presumably reports specs) without opening the schema.

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?

Implies you call it when you need platform-ready image variants and notes it is a paid call, but names no alternatives or exclusions among the six siblings (e.g. when to prefer omnipost_validate or omnipost_platform_specs). Usage is inferable rather than stated.

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