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

Beyond the readOnly/destructive/openWorld annotations, it discloses two non-obvious behavioral facts: the operation cannot mutate funds, and it cannot read another account's balance. It also states a real authorization constraint — linked agents are refused, person-only — which is not derivable from the annotations or schema.

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?

Four short sentences, each doing distinct work: purpose, parameter behavior, sibling routing, then authority limits. The core action is front-loaded in the first clause with no filler.

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 an output schema present, return shape need not be explained, and with a single enum parameter plus annotations, the remaining burden is authority and scope — both addressed by the person-only refusal and the cannot-move-funds statement. Nothing needed to call it correctly is missing.

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 0% and the enum values carry no descriptions, so the description must carry the load; it explains "activity" (latest 50 transactions, no paging) well. It never states what "summary" returns or which value is the default when view is omitted, leaving one documented gap for the only parameter.

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?

"Read your purchased Credits balance" gives a specific verb (read) plus a precisely scoped resource (purchased Credits balance), and the very next clause contrasts it against the included-coverage balance. An agent can distinguish this from account_get_usage without opening either schema.

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 description names the sibling account_get_usage and states exactly what that tool covers ("weekly included coverage and spending"), which routes the agent correctly. It also gives the condition for the parameter choice: use view="activity" when the last 50 transactions are wanted, with the caveat that there is no paging.

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