Generate the thumbnail of a page in the Docling document

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 adds the local-cache precondition, which is useful, but doesn't disclose what happens if the document is missing, how the image is returned, or any other behavioral details beyond the annotation coverage.

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?

The description is short and front-loaded, but it is redundant: 'generates a thumbnail image for the requested page' appears in both sentences. The second sentence does add the local-cache precondition, but it repeats the main action unnecessarily.

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?

The tool is simple, has complete schema documentation, and has read-only annotations, so the core requirements are covered. However, there is no output schema, and the description does not clarify what the tool returns or how the generated thumbnail is delivered, which is a notable gap.

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%, so all three parameters (document_key, page_no, size) are already documented in the schema. The description does not add additional semantics or examples beyond what the schema provides, so the baseline 3 is appropriate.

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 ('generates a thumbnail image'), the target ('the requested page'), and the key constraint that the document already exists in the local cache. This distinguishes the tool from other document manipulation and cache-related siblings.

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 description clearly conveys the prerequisite that the document must already be in the local cache, which is essential context for when the tool can be used. It does not explicitly name alternatives or exclusion conditions, but the context is strong enough for an agent to understand the required state.

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