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

Annotations already cover readOnly/idempotent/non-destructive, yet the description still adds real behavioral context: dashboard_locked is disclosed as a UI prompt that does not stop tracking, and the site parameter is tied to an ownership-based visibility restriction. 'Read only.' duplicates the annotation rather than adding value, and the price list's shape is left unexplained.

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?

A single dense sentence front-loads the purpose and then enumerates the returned facts, which is the right order for an agent skimming definitions. The enumeration of status values is load-bearing given there is no output schema; only the trailing 'Read only.' is wasted because annotations already say so.

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 return-value burden and does it reasonably well by listing plan status values, trial end, cycle events, limits, dashboard_locked, and price list. It is nearly complete for a one-parameter read tool; the main residual gap is that non-owner behavior and the price list contents are only hinted at.

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?

Schema coverage is 100%, so the schema already documents accepted formats (domain, id, tb_ public id) and the optional conditions. The description still earns credit by explaining the semantic effect of the parameter — it resolves which account the billing data belongs to — and by tying it to the owner-only visibility rule, which the schema does not state.

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 clear verb+resource framing and enumerates the concrete contents of the billing payload: plan status with its value set, trial end, cycle events, site/people limits, dashboard_locked, and the price list. It is specific enough to distinguish this from generic reporting siblings, though it never names or contrasts with get_usage, which the agent might reasonably confuse it with.

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?

Usage is implied rather than stated: the agent can infer this is the roster of plan/limit facts, and 'With site, the account that owns that site; only the owner sees the details' gives an access context. But there is no explicit when-to-use guidance versus get_usage or the report tools, and no note on what happens when the viewer is not the owner beyond 'only the owner sees the details'.

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