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

Annotations already declare readOnlyHint=true, so safety is covered; the description still adds value with per-theme default behavior, a permission/execution note ('runs straight away'), and the return shape including the null post_id case. It does not specify pagination/auth details, but those are less relevant for a read of this scope.

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?

Dense and front-loaded with the primary purpose first, then param default, return shape, and alternatives. Every clause carries information, though the trailing 'Through Royally' note is slightly bolted-on.

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 no output schema, the description fully supplies the return shape ({ stylesheet, active, css, post_id }), default semantics, alternatives, and execution note — nothing an agent needs to invoke 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 both parameters are already documented, including the stylesheet default. The description restates the default and adds the useful note that each theme keeps its own CSS, but that addition is marginal against a fully documented schema — baseline 3.

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 ('Reads a theme's Additional CSS'), locates it in the WP UI, and distinguishes the resource from two closely related siblings by naming them directly (wp_update_custom_css, wp_get_global_styles).

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 routes the agent: use wp_update_custom_css to change it and wp_get_global_styles for block-theme global styles. The when-not conditions are named rather than implied.

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