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

Annotations already declare the tool read-only and idempotent. The description adds important behavioral context beyond that: it reads from the optional `key` argument or the same `Authorization` header used by gated tools, and reports month-to-date usage. This clarifies the tool's data source without contradicting any annotation.

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 sentences, front-loaded with the core purpose, and every clause adds information: what is reported, how the key is resolved, and what question the tool answers. No redundant wording.

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 simple read-only tool with one optional parameter, the description covers the operation, the inputs, and the kind of output. There is no output schema, so a bit more detail about the exact response shape would help, but the stated scope is clear enough for an agent to invoke it 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 schema already describes the `key` parameter at 100% coverage, so the baseline is 3. The description adds value by explaining that the key is optional and can be omitted when the client sends the key as a request header, which clarifies when and how the parameter should be used.

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 uses a specific verb and resource: 'Report the tiers of this MCP server' and the calling key's 'tier, status and month-to-date usage.' It also frames itself as 'the authoritative answer' to connection and entitlement questions, making its role unmistakable even among unrelated sibling tools.

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 to call this tool: whenever the agent needs to determine 'am I connected, and what do I have.' It does not explicitly name alternatives or exclusions, but no sibling tool serves the same subscription-status purpose, so the guidance is sufficient.

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