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

No annotations are provided, so the description carries the full burden. 'Get' implies a safe read, but the description says nothing about granularity of the returned series, pagination, result caps, or auth requirements. It usefully discloses the per-account vs. aggregate branching, but for a no-annotation tool that is only partial coverage.

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 short sentences with the core purpose front-loaded and no filler. The branching clause is placed logically after the purpose statement, though it slightly restates what the schema's accountId description already says.

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 3-parameter, zero-required, read-only query with a fully documented schema and no output schema, the description covers what is queried and the aggregate-vs-single behavior. The main omission is any hint about the shape or granularity of the returned history, which matters slightly without an output schema.

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 description coverage is 100% — startDate, endDate and accountId all carry their own descriptions including defaults and the 'omit for combined' rule. The description restates the accountId semantics but adds no new syntax, format, or constraint information, so the baseline 3 applies.

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?

States a specific verb and resource ('Get account balance over time') and clarifies the branching behavior: per-account history when accountId is supplied, combined balance otherwise. It is clear on its own, but it never names the adjacent tools (get_cash_flow, get_portfolio_balances) that an agent might 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?

The description gives conditional usage for its own parameter ('If accountId is provided... Otherwise...'), which is genuinely helpful. However it offers no guidance on when to prefer this tool over get_cash_flow or get_portfolio_balances, so routing among balance-related siblings is left to inference.

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