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

Annotations only declare it is a destructive, non-read-only write. The description adds the real blast radius ('Every page using it changes too') plus partial-update semantics (omitted keys preserved, null resets) and a preservation guarantee ('Order bump styling... is kept'), all beyond what the structured fields convey.

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 short sentences, each carrying distinct information (scope, side effect, merge semantics, read-only constraint), with the primary constraint and consequence front-loaded. No filler.

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 3-parameter mutation with an output schema and full annotation coverage, the description covers scope, side effects, partial-update behavior, and the read-only fallback. Nothing an agent needs to call it correctly is missing.

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 100%, so the schema already documents themeId, name, and variables. The description restates the merge/null-reset semantics that the variables schema description already spells out, adding no syntax or format detail beyond it; baseline 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?

States a specific verb and resource ('Change a theme') and scopes it ('you created'), which cleanly separates it from create_theme, get_theme, and delete_theme. An agent can identify the operation without opening the 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?

Explicitly states when this tool cannot be used ('Built-in themes are read-only') and names the alternative path for that case ('copy one with create_theme and baseThemeId'). That is a when-not plus a concrete alternative, which is the strongest form of routing guidance.

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