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

Annotations already declare readOnlyHint=true and openWorldHint=false, but the description adds substantive context the annotations cannot: the writeLock field is present only when writing is blocked, and unlocking requires a human using 'Unlock writing' in the project. That is exactly the kind of absent-field convention an agent would otherwise misread.

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 return payload is front-loaded in sentence one, with scope and caveats after it, so the highest-value information lands first. The parenthetical on plan limits and the writeLock sentence are dense but each earns its place; the paragraph is slightly overstuffed for a zero-parameter tool.

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 carries the burden of explaining return values, and it does: user fields, bound project, server time, and the conditional writeLock field. Nothing an agent needs in order to call this 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?

The tool takes no meaningful parameters (the single `_unused` entry has full schema coverage), so there is no parameter semantics to explain and the schema baseline applies. The description correctly spends no words on parameters.

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 first sentence names a specific verb ('Returns') plus three concrete resources (authenticated user with id/email/plan, session-bound project, server time), so an agent knows exactly what it gets. The mention of the X-Project-Id/active_project_id resolution mechanism further pins down the resource.

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 description gives a clear use case — verifying which API key resolved to which account and plan — which is enough for an agent to know when to reach for it. It stops short of naming alternatives such as get_active_project or get_config, so nothing explicitly excludes nearby tools.

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