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

Annotations already establish readOnly, non-destructive, closed-world behavior, so the description's extra value is the account prerequisite ("Needs a linked Siftivo account") and the mode-dependent return shape. It does not say how far back "recent days" reaches or whether the list is capped, which is the main behavioral gap.

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 the resource and its contents, then the alternate mode, then example intents, then the prerequisite. Every sentence carries information; the only slight unevenness is that the prerequisite is tacked on at the end rather than stated up front.

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 must convey the return shape and it does so in detail for both modes. The remaining gap is quantitative scope (how many recent days / whether results are truncated), which matters for an agent deciding whether it has enough data.

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 both parameters are already documented, including the title-or-workId duality of `book` and the YYYY-MM-DD requirement for `today`. The description reinforces the mode switch but adds little syntactic or semantic detail beyond the schema, so the baseline 3 applies.

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 names a specific resource (the linked reader's reading journal) and itemizes exactly what comes back: current books, tracking mode (pages or audio time), position, totals, and whether today has an entry. It also defines a second mode when `book` is supplied. It is clear against read-oriented siblings like get_my_book, though it never explicitly contrasts itself with any named sibling.

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?

Concrete trigger phrases are given ("what am I reading", "where was I in X", "what did I write about X this week") plus the rule for the optional parameter: supply `book` for one book's days and notes, omit it for everything currently being read. No explicit when-not or named alternative is offered, 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.