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

Annotations already declare readOnlyHint, idempotentHint and destructiveHint=false, so the safety profile is covered. The description adds genuine operational context beyond that: reusing the same chart hits the shared cache, and the scope matches the rendering route. It does not say what certification produces or how failures surface, so it is only a moderate add.

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 sentences, front-loaded with the action, which is good. But the second sentence loops back to 'the route' in a way that adds words without adding information, and the third sentence mixes the cache note with the fallback pointer, blurring the structure.

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?

The description correctly delegates the enormous chart schema to viz_render's contract, which is sensible. However, on a no-annotations-output tool it never states the return value or the kind of artifact certification yields, and 'certifies the resulting normalized spec' is undefined. Adequate but incomplete for a tool whose whole purpose is producing a certification.

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 schema already documents the single 'chart' parameter exhaustively. The description adds the one useful pointer, that 'chart' is the viz_render input shape, which is not obvious from the schema alone. Otherwise it repeats schema territory, so baseline 3.

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 the verb 'certify' and the object 'a chart' and the route ('the same route'), but pivots immediately to referring to itself in the third person ('the route draws it and certifies the resulting normalized spec in the same scope'), which is confusing. It never plainly says what certification means or what the tool returns, and it does not clearly differentiate from viz_render, the tool whose input it consumes.

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?

Gives one clear routing rule: for arbitrary normalized specs, use local stdio instead. That is an explicit alternative with a condition. But it does not explain when to certify at all versus when to just call viz_render, so the primary use case is left implied.

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