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

Annotations already provide destructiveHint=true and idempotentHint=true, so the description does not need to restate those. It adds the Scale plan requirement and clarifies that this is a partial update, which is useful behavioral context beyond the annotations. No contradiction exists.

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 a single sentence that front-loads the action and scope, then adds the plan requirement. There is no filler or redundant repetition of schema information.

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?

Given the rich schema, output schema, and annotations, the description is complete enough for an agent to invoke the tool correctly. It includes the plan requirement, and the schema covers parameter semantics and replacement behavior. The only missing element, explicit alternatives, is already evident from sibling tool names.

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%, and the schema thoroughly documents id, tokens replacement semantics, and customFonts replacement. The description adds no parameter-level detail beyond 'by id', so the baseline of 3 applies.

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 states a specific verb ('updates'), a resource ('theme'), and a scope ('by id', 'partially'), which clearly distinguishes it from create_theme, delete_theme, get_theme, and list_themes. The plan requirement adds useful context without obscuring the core purpose.

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 phrase 'partially updates a theme by id' makes clear this is for modifying an existing theme, not creating, deleting, or reading one. It does not explicitly name alternatives or exclusions, but the context 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.