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

With no annotations, the description must carry the full burden, and it does well: it discloses the execution model (fetches the URL or parses raw JSON, runs checks server-side, no browser needed) and enumerates what is actually checked. It does not mention auth, rate limits, or failure modes on an unreachable URL, so it stops short of 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?

Front-loads the core purpose and return shape, which is good, but it spends several sentences on positioning ('fills this gap', 'the only validator that checks both') and DTCG background that inform the agent less than the operational facts. It is longer than it needs to be for a two-parameter validator.

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?

Although no output schema exists, the description supplies the return structure ({ checks[{id, name, status, detail}], valid, score }), the check count/range, and the input mode selection. Combined with the usage guidance, an agent has everything needed to invoke it 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?

Schema coverage is 100%, so baseline is 3, but the description adds a genuine constraint beyond the schema: the mutual exclusivity of url and lottie_file ('Provide exactly one'). That resolves an ambiguity the schema alone leaves open.

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 (validate) and resource (Lottie animation file) with concrete scope (Lottie spec v1.0.1 plus Designesy §16 Motion Standards, returning checks m01-m10). It explicitly differentiates itself from the sibling designesy_score by naming it in the 'When NOT to use' clause.

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?

Provides an explicit when-to-use case ('verify a motion/animation asset is well-formed AND accessible') and a when-NOT-to-use case that names the alternative tool ('for full-site motion scoring ... use designesy_score'). This is exactly the routing guidance an agent needs.

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