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

Annotations already declare readOnlyHint, openWorldHint, idempotentHint, and destructiveHint=false, so the description goes beyond by explaining subtle behaviors: null maxMapsPerProject means unlimited, Admin accounts receive Studio capacity without a subscription, Free is fixed at 720×480, and saved larger maps remain editable/exportable but not resizable. This is rich context the annotations cannot 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?

The description is long but every sentence carries operational value: return format, mapLimits interpretation, plan differences, admin exception, free-tier behavior, and error routing. It is front-loaded with the core purpose and only slightly verbose in the mapLimits explanation.

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 must carry the full burden of explaining return values, and it does thoroughly — enumerating userId, username, keyId, keyName, scopes, and mapLimits, then detailing each mapLimits subfield and its edge cases (null limits, side limits vs area limits, resizing rules). Nothing an agent needs to interpret the response 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?

The tool has 0 parameters with 100% schema coverage, so there is nothing for the description to add on parameters. The baseline of 4 applies — the description instead productively explains return-value semantics, which is the relevant information for a no-argument tool.

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 states a specific verb and resource ('Verify the API key and report which powers it has') and enumerates the return fields. This clearly differentiates it from the 60+ sibling tools, none of which deal with authentication or key introspection.

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?

Explicit guidance is given: 'Call this first when a tool fails with a scope error — the scopes array tells you what this key can and cannot do.' It also instructs when to read effective limits and saved maps before recommending dimensions, giving the agent a clear decision procedure.

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