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

Annotations already declare readOnlyHint=false, idempotentHint=false, and destructiveHint=false, covering the mutation and non-idempotent nature. The description adds a useful behavioral detail: 'No credits are charged for the upload.' It does not discuss error handling or side effects, but given the annotation coverage, this is adequate.

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?

Two sentences with no fluff. The core purpose is front-loaded, and the downstream usage is explained concisely. The extra note about credits is a minor but valuable addition. It is efficiently structured.

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 simple upload tool with only 2 well-documented parameters and no output schema, the description covers the return value (fal URL) and how to use it downstream. It lacks explicit error scenarios, but that is not critical for this tool type. Overall it is complete enough for an agent to invoke correctly.

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 100% – both parameters (imageUrl and imageBase64) already have detailed descriptions including format and size limits. The description reinforces the 'alternative' relationship between the two but adds no new semantic information beyond that.

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?

The description clearly states the action: uploading an image (URL or base64) to FATTLY and returning a fal URL. It explicitly explains the purpose: to obtain an inputImageUrl for downstream generation tools, and names the specific siblings it feeds into, distinguishing it from those tools.

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?

It explicitly tells when to use it: to turn a picture into an inputImageUrl for editing/face-swap/image-to-video models, and specifies that the returned URL should be passed as inputImageUrl to fattly_generate_image or fattly_generate_video. This effectively routes the agent to the correct workflow and alternatives.

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