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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive, closed-world), so the bar is lower, and the description still contributes two non-obvious traits: per-call access re-checking (auth context) and a 400-word cap per passage. It does not describe error behavior when the locator has expired, which would complete the picture.

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 with zero filler; the core action is front-loaded and the access and length constraints follow in order of decision relevance. Nothing is repeated from annotations or schema.

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 simple 3-parameter read tool with full schema coverage and no nested objects, the description covers what the tool returns (a passage plus neighbors, capped at 400 words) and the auth model. Only the failure mode for an expired/invalid locator is left unaddressed.

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 description coverage is 100%, so all three parameters (before, after, locator) are already documented with bounds, defaults, and the 24-hour locator lifetime — baseline 3. The description reinforces the 'nearby paragraphs' semantics of before/after and adds the word cap, but adds no format or edge-case detail beyond the schema.

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?

Specific verb + resource + scope: 'Read a located paragraph with nearby paragraphs for the signed-in member.' An agent can distinguish it from search_in_book (which produces locators) and from summary-oriented siblings. It stops short of naming an alternative explicitly, and the title merely restates the name.

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: 'located paragraph' plus the schema's note that locator comes from search_in_book suggests this is a follow-up call, but the description never states when to prefer it over get_chapter_summary, get_book_outline, or a fresh search_in_book. No exclusions or prerequisites are given in the description text itself.

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