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

Annotations already declare readOnlyHint=true, so the description's 'Read-only' simply restates structured data. It does add one genuinely useful behavioral fact: total debits equal total credits when the books balance, which tells the agent what a balanced result looks like. No mention of permissions, pagination, or basis behavior, but with annotations covering safety this is adequate.

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 plus 'Read-only.' Front-loaded with the core purpose and no wasted words. The trailing 'Read-only' is redundant against annotations but costs little.

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?

An output schema exists, so return values need not be re-explained. For a read-only report tool with one required parameter, the description is minimally complete, but the five under-documented parameters and unfiltered sibling landscape leave real gaps.

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 only 20%, so the description carries a heavier burden, yet it adds no parameter meaning. 'For a period' vaguely implies startDate/endDate but does not clarify the enum basis values, the required companyId UUID wrapper, or currency code semantics. It fails to compensate for the coverage gap.

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: returns every account's debit and credit totals for a period. This is clear and distinct from a general ledger or balance sheet at a conceptual level, though it never explicitly contrasts itself with those siblings. Clear purpose without sibling differentiation.

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 guidance on when to choose a trial balance over the many sibling report tools (balance_sheet, profit_and_loss, general_ledger). No prerequisites, no exclusions, no alternatives named. The agent must infer usage from the name alone.

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