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

Beyond the annotations (idempotent, non-destructive), the description discloses the 1-credit cost and the temporary download link validity (15 minutes). These are non-obvious behavioral facts critical for an agent's decision-making and not available from the schema or annotations. No contradiction with annotations exists.

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 crisp sentences, each providing essential info: core operation, requirement, input formats, cost, and output behavior. No filler, front-loaded with the primary purpose, and structured for quick comprehension.

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?

Given schema covers parameters fully, annotations cover idempotency/destructiveness, and description covers cost, output link expiry, and input formats, nothing an agent needs to correctly invoke the tool is missing. The absence of an output schema is mitigated by the explicit return description.

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%, so baseline is 3. The description adds valuable cross-parameter constraints ('Provide at least one of width, height, format or quality') and lists accepted input formats, both of which go beyond the schema. It does not repeat schema descriptions, so it earns above baseline.

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 states specific operations (resize, convert, compress) on a clear resource (ONE image), and explicitly lists conversion formats and input formats. It is readily distinguished from all sibling tools, which target PDFs, HTML, QR codes, etc., making the tool's unique purpose unambiguous.

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 gives clear context: the tool handles a single image and requires at least one of width, height, format, or quality. It does not explicitly name alternative tools for exclusion, but the operation space is so distinct from siblings (PDF manipulation, HTML conversion, ZIP creation) that an agent is unlikely to confuse them. No explicit when-not-to-use guidance is provided.

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