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

Annotations only declare readOnlyHint=true; the description adds the non-obvious behavioral fact that this tool is gated behind an account-level authentication step and cannot be reached through start_login. That is meaningful context the annotation does not carry. It still says nothing about behavior when unauthenticated or about caching, so it is not a 5.

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 short blocks, each earning its place: the first states what is returned, the second states the access constraint before the agent wastes a call. Front-loaded and waste-free.

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 and no parameters, the description must carry the whole load, and it does list the returned fields plus the auth gate. The only soft spot is the absence of any note about what happens on an unauthenticated call, which an agent would need to recover correctly.

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 per the rubric the baseline is 4. The description cannot and need not document parameter semantics; the enumerated return fields belong to purpose/scope rather than 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?

States a specific verb+resource ('Get the current subscription details') and enumerates the payload (plan, status, billing period, usage limits), so an agent knows exactly what comes back. It does not differentiate itself from adjacent siblings like get_usage, get_platform_summary, or get_settings, which is the only thing keeping it from a 5.

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 ACCESS block gives a real prerequisite (needs a Proof account, client must authenticate via /mcp) and explicitly rules out the obvious alternative by stating 'start_login does NOT open this tool.' That is genuine when-to-use and when-not-to-use guidance, though it stops short of telling the agent what to do if authentication fails.

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