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

Annotations flag destructiveHint=true and idempotentHint=true, and the description earns its keep by disclosing the blast radius — "Every demo that uses the kit renders with the change, published ones included" — which is exactly the cascade an agent must warn about. It adds two side effects not in any structured field: font files are self-hosted on save, and null colors re-derive from accent/contrast.

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 verb and the field inventory, and every clause carries information (partial-update rule, cascade warning, plan gating, scopes). It is densely compressed into one paragraph with nested parentheticals, which is efficient but slightly harder to scan than separated prerequisite and effect statements.

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 12-parameter mutation with a nested colors object, no output schema, and a destructive cascade, the description supplies permissions, plan gating, partial-update behavior, null semantics, and downstream render impact. The only omission is the return value, which is acceptable absent an output schema.

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?

At 75% schema coverage the schema already explains accent, tooltip, radius, themeId, fonts, and ctaLabel. The description still adds real meaning the schema lacks: null color values re-derive from accent and contrast, and headingFont null falls back to the body font. It doesn't cover the remaining nested color keys or makeDefault's const constraint beyond naming it.

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?

Opens with a specific verb+resource ("Changes a brand kit") then enumerates the exact editable surfaces: name, accent, colors, tooltip surface, fonts, radius, brand name, header button, default flag. This clearly separates it from get_brand_kit / list_brand_kits in the sibling set, which are read operations on the same resource.

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?

"Fields you leave out stay" establishes partial-update semantics, and "Pro and Team (Free can only rename)" plus the required scopes tell the agent when the call is even permitted. It stops short of naming a sibling alternative (e.g. create vs. edit, or bulk vs. single-field paths), so there's no explicit when-not guidance.

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