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

The description adds substantial behavioral context beyond the readOnlyHint annotation: 'plan, seat and top-up changes are not available through MCP by design — a human does those in the web app.' This discloses limitations and redirects the agent appropriately, making the tool's behavior fully transparent.

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?

Three sentences, each earning its place: the first states the purpose and output, the second differentiates from siblings and notes permissions, the third discloses read-only design and web-app fallback. No redundancy or fluff; the key information is front-loaded.

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 no-parameter, read-only tool with no output schema, the description covers all necessary context: what is returned, what permissions are needed, what context is required, and what actions are intentionally unavailable. An agent has everything needed to call and interpret the tool.

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 zero parameters, so the description correctly does not attempt to explain any. Per the rubric, 0 params warrants a baseline of 4; the description adds no unnecessary parameter detail, and the baseline is appropriate.

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 clearly states the resource (the organization's trial) and enumerates the specific information returned: tier, running status, expiry, and days left. It is distinct from sibling tools by explicitly contrasting with 'other billing tools' and specifying the permission difference.

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?

Provides explicit guidance on when to use this tool vs alternatives: 'Unlike the other billing tools this one only needs organization membership, not billing:read.' It also states the prerequisite 'Requires organization context.' This fully informs an agent on selection and prerequisites.

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