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

Goes well beyond the annotations: discloses cost (3 credits) and, critically, that it is 'charged only when a call succeeds', plus the exact return payload (hosted PNG URL, same image as b64_json, aspect ratio and size used). For a generation tool with no output schema, that return-shape and billing disclosure is exactly the context an agent needs.

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?

Four tight sentences: purpose, payload, usage-plus-alternatives, cost. Nothing is redundant with the schema or annotations, and the routing information (bg-remove/screenshot) is front-loaded where an agent will see it before committing.

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 fully compensates by enumerating return fields; with annotations silent on billing, the cost model is spelled out. Nothing needed to invoke this correctly — purpose, inputs, outputs, cost, and sibling routing — 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 100% and both parameters are documented there, so the schema carries the semantics. The description confirms that aspect ratio and size come back from the call but adds no new detail about allowed values, defaults, or prompt constraints beyond the enum already in the schema. Baseline 3 applies.

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 ('Generate images from text prompts') and immediately pins down scope against the two nearest siblings (bg-remove for background removal, screenshot for web capture). An agent can distinguish this from every sibling in the list 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?

Explicit 'use to create a new picture from a description' plus two named alternatives with the exact condition that selects each ('cut the background out of an existing image', 'capture a web page'). This is the when/when-not/alternatives pattern at full strength.

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