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

Annotations already declare destructiveHint=true and readOnlyHint=false, so the write/replace nature is partly covered; the description corroborates this by saying it 'replaces the look Marsell would otherwise read from the site,' adding real context about what is being overwritten. It does not say whether the previous look is recoverable, whether a second call fully replaces versus merges with existing values, or whether a prior setup state is required, which are the remaining behavioral gaps for a destructive write.

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 core purpose and the fill_setup dependency are front-loaded in the first clause, followed by the field enumeration. It is a single dense sentence that occasionally runs on (the mid-sentence field list could be trimmed since the schema repeats it), but nothing important is buried and there is no filler prose.

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?

With seven parameters, full schema coverage, and no output schema, the definition covers what the tool is, what it accepts, and where the adjacent colours/fonts live — enough to invoke it correctly. What it omits is replace-versus-merge semantics on repeat calls and any setup prerequisite, which matter given the destructive annotation but are a moderate rather than disqualifying gap.

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 every one of the seven parameters is already documented in the schema itself. The description enumerates the same content types (summary, aesthetics, design rules, motifs, typography, photography, what would break it) and marks some as optional, but adds no format, length, or example guidance beyond what the schema properties already provide. Baseline 3 applies when the schema carries the explanatory load.

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 opens with a specific verb and resource ('Sets the brand's look, the design language') and immediately scopes its influence ('every picture and film Marsell makes stays inside'), which tells an agent exactly what downstream behavior this governs. It also separates itself from the sibling fill_setup by stating 'The colours and fonts come from fill_setup,' so the boundary between the two brand-configuration tools is legible without opening either 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?

Usage is implied rather than stated: 'It replaces the look Marsell would otherwise read from the site' signals this is an override of a site-derived default, which is genuinely useful context for choosing it. However, there is no explicit when-to-use/when-not language, no prerequisite ordering (e.g. must fill_setup run first), and no mention of related siblings like update_brand or add_guide that an agent might otherwise reach for.

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