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

The description confirms the write operation nature ('save or update') consistent with annotations (readOnlyHint: false, destructiveHint: true), and mentions the optional nature of notes. However, it does not elaborate on the destructive implications of updates, the non-idempotent behavior, or what happens to existing data when updating.

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 zero waste: first establishes core functionality, second covers the optional note constraint. Information is front-loaded and appropriately sized for the tool's complexity.

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?

Given the presence of comprehensive annotations covering safety/destructive hints and full schema coverage, the description provides adequate context for a straightforward 3-parameter mutation tool. It appropriately omits return value details since no output schema exists to describe them.

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 100% schema description coverage, the schema already documents all parameters (book_id, state, note). The description mentions the note parameter's optional status and character limit, but this largely restates schema information. It adds no semantic context for book_id or state parameters, warranting the baseline score.

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 'Save or update a bookmark for a book' — specific verbs (save/update) plus specific resource (bookmark). It effectively distinguishes from read-only siblings like list_bookmarked_books, get_book_details, and explore_books by emphasizing the mutation aspect.

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 implies usage through 'Save or update' clarifying it handles both creation and modification, but provides no explicit guidance on when to use this versus list_bookmarked_books (which reads bookmarks) or other siblings. No when-not-to-use or prerequisites are mentioned.

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