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

Annotations already declare readOnlyHint=true and destructiveHint=false, so the safety profile is covered. The description adds genuine behavior detail — that it reports access-denial reasons, connected Google services, and a disabled-resource count — but says nothing about cost, freshness, or whether the checks are live versus cached.

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?

A single sentence that front-loads the primary subject (the signed-in user) and then enumerates the rest. The field list is long but each item is a meaningful discovery cue; it does not repeat the title or pad with 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?

With no parameters, an output schema present, and annotations covering safety, the remaining burden is just to tell an agent what the call is for — which it does. The only gap is the absence of any prerequisite or when-to-use framing.

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?

The tool takes zero parameters, so there is nothing for the description to disambiguate and no risk of misuse. Baseline for a no-parameter tool 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?

"Show the signed-in user, their Metrinel plan and tier... whether access is allowed and why not" gives a concrete verb plus a specific set of account-level facts, which clearly separates it from the data-fetching siblings (ads_*, ga4_*, gsc_*). The distinction is inherent in the content rather than stated, so it falls short of explicit sibling differentiation.

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 usage context is only implied: an agent can infer this is the tool to call to check sign-in, plan limits, or whether access is blocked and why. There is no explicit "use this when..." statement, no exclusions, and no mention of prerequisites such as needing to be authenticated first.

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