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

Annotations only flag destructiveHint/idempotentHint/readOnlyHint=false; the description explains the actual risk: 'Each field given replaces what the reader had there before', so callers must not resend a rating or note unless it should change. It also discloses the auth prerequisite ('Needs a linked Siftivo account') and the no-op semantics of omitting readingStatus, all beyond structured data.

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 core action and shelf values, then routing, then replace semantics. It is dense and the worked example phrases slightly overlap with the usage sentence, but nearly every sentence carries distinct information and none is filler.

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 5-parameter mutation with no output schema, the description covers the operation, prerequisites, defaults, and overwrite behavior well. It does not say what happens on an unknown workId or a failed write, which is the only notable gap.

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 already 80% (notes, rating, progress, readingStatus all documented), so the baseline is 3. The description adds genuine meaning on top: workId provenance (search_books), the combined readingStatus+rating pattern with a worked 4.5 example, and the replace-not-merge semantics of each field.

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 and resource (add/log reading on the reader's shelves) and enumerates the exact operations: shelving to NOT_STARTED/READING/FINISHED/DNF, rating, progress. It is clearly separable from siblings like remove_from_library and get_my_library without opening any schema.

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 concrete user phrasings that should route here ('add X to my list', 'I just finished X, four stars', 'I'm halfway through X') and names search_books as the source of workId, so the agent knows the prerequisite call. It also states the default behavior when readingStatus is omitted, removing the main ambiguity about when a minimal call is appropriate.

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