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

Annotations already cover the safety profile (readOnly=false, destructive=false, openWorld=true, idempotent=false), so the bar is lower, and the description still adds real behavior: a 100-entry batch cap and the requirement that `image_url` be a public https link. It does not address duplicate handling despite idempotentHint=false being the notable risk here, which keeps it from a 5.

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?

Three tight sentences with the single/batch distinction front-loaded and no filler. The phrasing 'title and the rest at the top level' is slightly compressed to the point of ambiguity but still readable at a glance.

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 14-parameter, zero-required tool with a nested `entries` object and no output schema, the description omits important call-shape details: that the schema carries a flat top-level variant of every field that mirrors the per-entry keys, and that `shelf` and `shelf_id` are alternatives to one another. An agent must open the schema to assemble a valid call.

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 86%, so the baseline is 3, but the description adds meaning the schema does not: `status` has no description or enum in the schema, and the description enumerates the accepted values plus the open-ended case of the shelf's own custom word. The single-vs-batch structural guidance and the https constraint on `image_url` go beyond the schema as well.

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 verb and resource ('Add one entry ... to one of their shelves') and splits the two modes of operation (single entry via top-level fields vs. many via `entries`), which an agent could not infer from the name alone. It stops short of differentiating itself from close siblings such as `add_item`, `add_to_list`, and `bulk_add_items`, so a 4 rather than a 5.

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?

It implicitly tells the agent when to use the batch form ('one entry ... or many, up to 100'), which is useful routing guidance. However, there is no explicit statement of when to prefer this over `add_item` or `bulk_add_items`, and no mention of prerequisites such as whether the shelf must already exist or what happens on duplicates for this non-idempotent tool.

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