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

readOnlyHint=true already tells the agent this is a safe read, so the description's job is to disclose what comes back, and it does: field-by-field contents, the ISO8601 format of defaultDueNext, and the null case for quietHours when the feature is off. It doesn't say whether account fields themselves can be null (e.g. trialStartedAt for non-trial users), which is the one behavioral gap.

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 listing the return payload, followed by a short imperative on when to call it. The return-value clause is packed but well ordered, and the operational instruction is placed last where it reads as the takeaway; nothing is redundant.

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 must carry the entire return contract, and it does so thoroughly for a no-parameter read tool: all fields, the date/weekday computation basis (the account's timezone), the ISO8601 format, and the quietHours null case. Only the nullability of the account fields themselves is left unstated.

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?

There are zero parameters, so the baseline is 4 and there is nothing for the description to disambiguate. The description correctly spends its space on return semantics instead of inventing parameter detail.

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 operation and enumerates exactly what is returned: the Account record fields (trialStartedAt / subscribedUntil / timeZone / defaultTime), today's date and weekday in that timezone, defaultDueNext in ISO8601, and quietHours with a null case. That level of enumeration makes it unmistakable against the todo-CRUD siblings.

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 an explicit trigger condition: call this before handling dates, which is exactly the prerequisite an agent needs to know. It stops short of naming alternatives or stating when-not-to-call, but the sibling set (todo operations) is far enough away that no routing ambiguity remains.

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