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

Annotations already cover readOnly/idempotent/non-destructive, but the description adds real behavior: an auth requirement (Owner or Admin) and a result-shaping exclusion (Owner, Admin, Billing are omitted because the rule changes nothing for them). These are details an agent cannot get from the annotations or schema alone.

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 dense sentences, front-loaded with what is returned and that nothing is written, then grounding and the exclusion rule. 'Nothing is written' partly echoes readOnlyHint but is short and clarifying; overall there is little wasted text.

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 read-only preview with full schema coverage and no output schema, the description explains the return conceptually (matching projects and people) and notes a non-obvious output caveat (excluded roles). Nothing needed to invoke or interpret 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 description coverage is 100%, so the schema already documents match, tags, userIds, and groupIds (including cross-references to list_members and list_access_groups). The description adds no per-parameter syntax or constraints beyond the schema, so the baseline 3 holds.

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 defines the operation concretely: it returns which live projects and people a rule would match, and clarifies nothing is saved. Combined with the read-only nature, an agent can distinguish it from create_access_rule/update_access_rule. It opens with a noun clause rather than a verb+resource, so it leans on the title, but the intent is unambiguous.

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?

It gives clear context for when this applies: a pre-save check ('if it were saved as described') that mirrors the New rule drawer, and states the prerequisite (needs Owner or Admin). It does not explicitly name create_access_rule as the follow-on, so the alternative routing is implied rather than spelled out.

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