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

Annotations already declare readOnly, idempotent, non-destructive and closed-world, so the safety profile is covered. The description adds real context beyond them: the result is scoped to the signed-in member, passages are restricted to titles the caller can open, and consumption is capped by a daily word limit.

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 tight sentences that front-load the primary output (plan and daily words left) and then qualify the scope. No filler or restatement of the title.

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?

With no output schema, the description does name the shape of the return (plan plus remaining word allowance) and the access constraint. It stops short of describing additional fields an agent might expect, such as words consumed today or reset timing, which for a quota tool would be useful.

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, so there is nothing for the description to disambiguate; the baseline of 4 applies. It correctly implies the member identity is derived from the session rather than passed in.

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 a specific verb (read) and two concrete resources: the member's plan and remaining daily words. That distinguishes it from the sibling read tools (get_passage, get_book, list_my_library), though 'the plan' is never defined and only the name/title disambiguate it as a reading plan.

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?

Usage is only implied: mentioning 'daily words left' and a daily word limit hints that an agent should consult this before reading, but it never says when to call it, when not to, or names any alternative (e.g., list_my_library for the shelf contents).

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