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

Annotations already declare readOnlyHint=true and destructiveHint=false, so the safety profile is covered. The description's one genuine addition is the cost disclosure ('Cost: 10 credits'), which is useful for an agent weighing expensive calls. It says nothing about size limits, unsupported-format failures, or processing latency that would matter for an upload-based tool.

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?

Total length is short, but it opens by restating the name twice ('WebP Converter: WebP Converter transforms...') and spends a sentence on filler ('Essential for handling modern web images'). The concrete value — direction of conversion, compression rationale, credit cost — is buried behind that redundancy rather than front-loaded.

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 an output schema present and full parameter documentation, the description needn't explain return values, so what remains is differentiation and constraints. It is adequate but incomplete: it omits any boundary conditions (max input size, allowed output formats beyond PNG/JPG) and gives no help disambiguating against ImageConverter in a very crowded sibling set.

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%, with every parameter documented including defaults and examples, so the baseline is 3. The description only marginally extends this by enumerating PNG and JPG as target formats, which is helpful given outputFormat has no enum, but it adds no meaning to quality, maxWidth, or maxHeight.

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 names a specific verb and resource ('transforms WebP images') and states both conversion directions (WebP to PNG/JPG and other formats to WebP), so the core operation is unambiguous. It does not, however, distinguish itself from the very similar ImageConverter, HEICConverter, and SVGConverter siblings, which an agent would need to choose among.

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?

The only hint of usage is the vague marketing line 'Essential for handling modern web images' and the passing mention of 'better compression'. There is no stated when-to-use, no when-not-to-use, and no reference to the sibling converters that overlap heavily with this one, leaving the agent to guess which converter to pick.

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