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

With no annotations, the description carries the behavioral burden well: it discloses file-size limits, daily and rate limits, branding on free-tier output, and how Pro resolves those constraints. It names specific error conditions (daily_limited, Pro-only) and the recovery tool. It stops short of stating whether input files are retained or what the returned payload looks like, so it is strong but not complete.

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 core action and input format are front-loaded in the first two sentences, followed by limits and upgrade routing. The pricing paragraph is somewhat longer than strictly necessary but remains useful for an agent that must handle refusals. Overall it is well structured with minimal waste.

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 five-parameter mutation-like tool with no output schema and no annotations, the description covers the important operational context: input shape, output features, limits, and upgrade handling. It does not describe the return payload format, but the schema's names field explains output naming and the remaining gap is modest.

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 schema already documents files, names, title, author, and dividers in detail. The description adds little beyond reinforcing base64 input and table-of-contents/dividers behavior. Baseline 3 is appropriate when the schema does the heavy lifting.

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 a specific verb and resource: merge multiple EPUB files into one ebook with a table of contents and chapter dividers. This clearly distinguishes it from siblings like split_epub, compress_epub, and the conversion tools. An agent can identify the operation without opening the schema.

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 preconditions (2+ base64-encoded EPUB files) and explicitly routes refusal cases to upgrade_to_pro when daily_limited or Pro-only errors occur. It does not explicitly say when to use this instead of split_epub or compress_epub, but the merge-specific purpose makes the intended usage evident.

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