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

Goes well beyond the readOnly/idempotent annotations: free, no key, no quota, and no call consumed. It also discloses concrete behavioral outcomes — reports engineEnabled, warns on parts whose bounding box fits no stock sheet, and for engine "max" returns 400/503 or an async warning matching the optimize path exactly.

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 key framing and the sibling pointer, but the "free / no key / no quota / no solve" idea is restated three times in the opening lines. The engine-max error-code detail earns its place; the repetition does not.

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 deeply nested 5-parameter request with an output schema, the description supplies the validation semantics, the response highlights (engineEnabled, fit warnings), and engine-specific failure modes. The remaining gap is that field-level meaning is outsourced to optimize_nest rather than restated.

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 0%, so the schema itself documents nothing, and the description defers parameter meaning to optimize_nest ("field descriptions there"). That cross-reference is genuinely useful and the only param-specific note (engine "max") is accurate, but an agent still has to fetch another tool's schema to learn what parts/stock/options require.

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 — schema-validates a nesting request without solving it — and immediately anchors it to the sibling it shadows ("Same arguments as optimize_nest"). An agent can distinguish it from optimize_nest and validate_2d/validate_1d 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?

Makes the selection condition clear: use this to check a request without spending a solve call or quota, and it explicitly points to optimize_nest as the solving counterpart. It does not spell out a "when not to use" case or contrast against the other validate_* siblings, so it stops just 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.