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

Beyond the annotations (safe mutation, not idempotent), the description discloses a genuine side effect: chapterTitle silently creates a chapter if one with that title is missing. It also gives the length cap and default grouping behavior, though it doesn't mention any failure modes or what is returned.

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?

Three tight sentences, front-loaded with purpose and then branching behavior. The 'Up to 2000 characters' line duplicates the schema maxLength slightly, but it sets a practical constraint the agent should know before composing.

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 tool with no output schema, the coverage is strong: creation side effects, defaults, and length limits are all stated. It stops short of covering the userBookId and page parameters, which an agent may guess but should not have to.

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?

With only 20% schema coverage, the description carries the parameter burden well: it explains the chapterId source, the create-on-miss behavior of chapterTitle, and the 'General notes' default. The userBookId and page parameters are left unexplained, which is the main gap.

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 first sentence names a specific verb and resource ('Adds a note or a quoted passage to a library book'), which immediately distinguishes this from the sibling tools edit_note and delete_note.

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 clearly explains the routing between chapterId (taken from list_notes) and chapterTitle, and states the fallback of 'General notes' when neither is given. It does not explicitly tell the agent when to use this tool instead of edit_note, but the create-versus-modify distinction is obvious from the verb.

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