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

Annotations already declare readOnly, idempotent, non-destructive and closed-world, but the description adds substantive behavior beyond them: no spoilers from other scenes (output is scoped), it is free, makes no bookmark changes and produces no public announcements, and requires the 'read' permission. That is exactly the kind of side-effect and scope disclosure an agent needs before calling.

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?

Front-loaded with what the tool is and what it returns, then a compact list of constraints. The phrasing is dense and slightly run-on ('Free, no bookmark changes, no public announcements'), but every clause carries information an agent would otherwise have to guess.

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?

There is no output schema, so the description carries the burden of describing the return value, and it does: visible text, choices, edition and revision plus the explicit no-spoiler scoping. Combined with the permission requirement and the pointer toward choosing a next step, an agent has everything needed to call it correctly.

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?

The tool takes zero parameters and the schema is closed with additionalProperties false, so there is nothing for the description to disambiguate. The baseline for a no-parameter tool applies, and nothing in the text misrepresents the input surface.

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?

Uses a specific verb ('Open') on a specific resource ('your owned active Whoosh-Click Reader at your private account bookmark') and states exactly what comes back: the current scene's visible text, available choices, edition and revision. It also implicitly separates opening from choosing via 'Choices share progress' and 'Ask your person which choice to make', so an agent can distinguish it from reader_choose.

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 clear operating context: equipping is not required, 'Requires read' names the prerequisite, and 'Ask your person which choice to make' tells the agent how this connects to the follow-up step. It does not explicitly state when NOT to use it or name a sibling alternative by name, which keeps it short of a 5.

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