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

The description goes well beyond the readOnlyHint annotation by disclosing fail-closed behavior ('returns ok=false with precise errors') and the critical warning semantics that warnings[] can be non-empty while ok=true, tying it to WCAG 2.2.2/reduced-motion. This is genuinely valuable behavioral context that annotations alone do not provide.

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?

The description is dense and efficient: the first sentence states the core action, the second explains fail-closed and returns, and the third highlights the critical accessibility nuance. Every sentence earns its place with no redundant or filler wording.

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?

Despite having no output schema, the description explicitly enumerates the return shape ({ok, errors, warnings, deprecations, catalogVersion}) and explains the non-obvious semantics (warnings non-empty with ok=true). Combined with the single well-documented parameter and clear annotations, this gives an agent everything needed to invoke and interpret the tool correctly.

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?

The input schema already has 100% coverage for the single 'spec' parameter with a description, so the baseline is 3. The tool description adds high-level validation context (what is checked) but does not add specific parameter syntax or formatting details beyond the schema, so no score above the baseline is warranted.

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 uses a specific verb ('Checks') and clearly identifies the resource being validated (a MotionSpec), listing the exact validation dimensions: schema, primitive allow-list, parameter bounds, and injection rules. This also distinguishes it from the sibling motion_catalog by making clear this is a validation/trust-boundary tool, not a catalog lookup.

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?

The description provides explicit guidance on when to use the tool: 'Use to pre-check a spec before compiling.' This gives clear context and a practical usage trigger. It does not explicitly name alternatives or state when not to use it, but the guidance is strong enough for an agent to select it appropriately.

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