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

Annotations already declare readOnlyHint=true, openWorldHint=true, destructiveHint=false, covering the safety profile. The description adds genuinely new context by enumerating the returned fields (location rules, REST visibility, field count), which matters because there is no output schema. It does not mention pagination or scale limits.

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 tight sentences with zero filler: the first front-loads what is returned, the second supplies the use case. Nothing could be removed without losing 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?

With no output schema, the return-field enumeration is what makes this definition callable and interpretable, and annotations cover safety. Only minor gaps remain (ordering, whether inactive groups are included, large-site behavior).

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?

One optional parameter with 100% schema description coverage, so the schema already documents site_id fully. The description adds no format, default, or multi-site behavior detail beyond the schema; 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 (list) and resource (ACF field groups) and enumerates exactly what each entry contains: key, title, active status, location rules, field count, REST visibility. It distinguishes itself from acf_get_field_group by implication only (list-all vs. fetch-one), so it is clear but does not explicitly name the singular sibling.

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?

"Use this to discover what custom fields are configured on the site" gives a clear context for invocation. It does not name alternatives or exclusions (e.g., use acf_get_field_group when you already know the key), so it falls short of full routing guidance.

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