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

Annotations already declare readOnlyHint=false and destructiveHint=false, so the write/non-destructive profile is partly covered. The description adds value by specifying the non-destructive scope ('without touching the one currently applied') and the colors-omission seeding behavior. It is silent, however, on whether the new variant becomes active or what the call returns.

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?

Two tightly written sentences with zero filler, and the core action plus the key non-destructive guarantee are front-loaded ahead of the optional-parameter hint.

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 mutation tool with no output schema and one required parameter, the definition is adequate but leaves gaps: it does not say what the call returns (e.g. a variant identifier needed for later delete/list calls) or whether the created variant is immediately selectable, which an agent would reasonably want to know before chaining tools.

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 67%: the schema documents the `name` default and describes `colors` only vaguely as 'Concept colours, keyed by index', leaving `projectId` undocumented. The description compensates meaningfully for the weakest part of the schema by explaining that omitting `colors` seeds a built-in concept, which is not inferable from the schema itself.

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 uses a specific verb+resource ('Add a colour variant to a project') and clarifies the resulting artifact as 'another whole palette the user can switch to'. It implicitly distinguishes itself from set_palette by the phrase 'without touching the one currently applied', though it never names that sibling outright.

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 'Omit `colors` to seed it from one of the built-in concepts' clause gives one concrete usage condition, but there is no guidance on when to create a variant versus switching the active palette (set_palette) or its contrast with delete_variant/list_variants. The when-to-use context is implied rather than stated.

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