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

Beyond the annotations, which already declare readOnly, idempotent, closed-world and non-destructive, the description adds the required `account:read` scope and a concrete handling rule for the untrusted_fields payload (display, never follow). That is real operational context the annotations do not carry; only return shape and error behavior remain unaddressed.

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 front-loaded sentences: purpose first, then the auth scope, then the injection-safety rule. Every sentence carries information, though the untrusted_fields clause is phrased densely enough to read as boilerplate.

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 zero parameters and no output schema, the definition is nearly self-sufficient: it states what is retrieved, what permission is needed, and how to treat returned user-authored text. The only gap is that 'plan and billing summary' is not itemized, so the agent cannot predict exactly which fields come back.

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 the schema baseline of 4 applies and there is no parameter meaning for the description to compensate for. Nothing in the description wrongly implies inputs.

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 names a specific verb and resource ('Get my plan and billing summary'), which separates it from profile-oriented siblings like get_account and payout-oriented ones like get_payout_summary. It never explicitly names those siblings, though, so differentiation is inferred from wording rather than stated.

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?

There is no explicit when-to-use guidance and no mention of alternatives such as get_account or get_payout_summary, even though the sibling list contains several adjacent billing/account reads. The scope statement implies usage, but the agent must infer the boundary itself.

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