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

Annotations already declare readOnly/idempotent/non-destructive, so the description's job is to add context — and it does: the ~200 item cap, category grouping, and the returned field set. It does not discuss whether results are cached or how the cap is enforced, 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?

Two compact sentences with zero filler, and the scoping/alternative information is front-loaded ahead of the filter note. Nothing is repeated needlessly.

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 zero-required-parameter filter tool with full annotation coverage and no output schema, the description is nearly sufficient — it names the returned fields and the result cap. Minor gap: it doesn't address how `id` (site id) interacts with the read, which the schema alone carries.

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 the baseline is 3. The line about `categories` / `styles` arrays OR-matching largely restates the schema's own "OR-filter by several" descriptions, adding emphasis rather than new semantics; the singular-vs-plural merge behavior is also already documented 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?

States a specific verb and resource (list library blocks), the scope (~200 items, grouped by category), and the fields returned (slug, name, tags). It also names the sibling it differs from, search_blocks, so an agent can distinguish the two without opening schemas.

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?

"A broad menu; search_blocks ranks and filters" gives an explicit alternative plus the condition that selects it. It stops short of an explicit when-not statement (e.g., avoid when you already know the target block), but the routing signal is clear.

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