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

Annotations already carry readOnly, idempotent, non-destructive and closed-world hints, so the safety profile is covered. The description adds real behavioral context beyond them: page size (60 items), newest-page-first paging, and the meaning of each marker kind (morning_after, between_dates, matched, date_agreed).

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 dense sentences, front-loaded with the resource and its contents, with cursor usage last. Every clause carries information, though the near-adjacent 'oldest first' and 'Newest page first' phrasing forces the reader to parse which axis of ordering is meant.

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 carries the return-shape burden and does so well: it explains the item kinds, the ordering, and paging. The only gap is the slight ordering ambiguity ('oldest first' vs 'newest page first') that an agent may need to resolve empirically.

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 coverage is 100%, so baseline is 3, but the description adds genuine meaning to the cursors — before: returns the page before, after: takes the newest id you've seen to fetch only new items — which is not spelled out in 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?

The description states a specific verb and resource: reading the full text thread between one of YOUR characters and someone it has dated. It clarifies scope (couple threads, message kinds, ordering) so an agent can distinguish it from send_text, but it never explicitly names or routes against a sibling tool.

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 implied by the resource rather than stated: read a thread. It does give practical guidance for the pagination parameters (when to pass before: vs after:), but offers no explicit when-to-use/when-not or alternatives.

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