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

Beyond the minimal annotations, the description discloses that DRM-protected books always fail and that pdf→epub reflows fixed pages causing quality to vary with layout complexity. It does not contradict annotations and adds meaningful runtime behavior, though it doesn't describe the return artifact or other side effects.

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 dense and front-loaded with the operation, formats, recommendations, and caveats. The redundant 'eBook Converter —' prefix and trailing '[category: convert]' tag add minor noise, but the core content is efficiently organized.

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 3-parameter conversion tool with full schema descriptions and no output schema, the description covers the key decisions: direction, quality caveat, DRM limitation, and routing. The main residual gap is the undocumented meaning of to=pdf and the lack of any statement about the returned artifact, which keeps it just below a 5.

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 value by constraining valid source→target directions and identifying epub→pdf as outside this tool's scope. Slight ambiguity remains because the to-schema includes pdf while the description only names epub/mobi/azw3 as targets, but the core format semantics are well-enriched.

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 the core operation with a specific verb and resource: 'Convert ebooks between formats with calibre', and enumerates the supported direction pairs (mobi/azw3/fb2/lit/pdf → EPUB, epub → mobi/azw3). It also differentiates from convert_document by explicitly routing epub→pdf elsewhere, so an agent can identify the right tool without inspecting schemas.

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?

Gives concrete selection criteria: EPUB is recommended for modern Kindles/send-to-device, DRM-protected books cannot be converted, and epub→pdf should go to convert_document (LibreOffice). This is an explicit when-to-use and when-not-to-use statement versus named alternatives.

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