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

With no annotations provided, the description carries the full burden. It discloses the key side effect (source unchanged, new file created) and states the return value (output path and max-side constraint). This covers the main behavioral traits; it does not mention edge cases like whether it upscales if the source is smaller, but that is not critical for a preview 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?

Two sentences with no redundancy. The first sentence front-loads the operation and core constraints; the second adds use case and return info. Every clause earns its place.

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 tool with full schema coverage, no output schema, and no annotations, the description covers operation, side effect, return value, and intended use. Minor gaps like behavior when the source is already smaller are acceptable and would not prevent correct invocation.

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 the baseline is 3. The description restates the size parameter's meaning (longest side) and adds aspect-ratio preservation, which is not in the schema. However, it doesn't significantly enhance parameter understanding beyond what the schema already provides.

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 operation (create downscaled preview) with the key constraint (max side, aspect ratio preserved) and explicitly mentions writing to a new file. The phrase 'downscaled preview' and 'NEW file' distinguishes it from potential siblings like resize or convert, even without naming them.

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?

Mentions an intended use case ('Ideal for generating small previews or contact sheets') but provides no explicit exclusions or contrast with sibling tools such as resize. Usage is implied rather than explicitly routed, leaving the agent to infer when thumbnail is preferable.

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