vendor_balances

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

With no annotations, the description carries the full burden and does disclose a non-obvious behavioral rule: payments are matched only in the vendor's own currency, so a mismatched-currency payment surfaces as an open balance. This is exactly the kind of semantic caveat structured fields cannot convey, though it does not state read-only nature or any rate/latency characteristics.

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?

Two tight sentences with the core output front-loaded and the caveat second; no filler, and the exception cross-reference to reconcile_ledger is placed where it is most useful.

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 formatting is covered elsewhere, and the description supplies the key semantic gotcha an agent needs. Only the read-only nature and the precise meaning of the currency filter remain 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?

Schema coverage is 0% and the single currency parameter's enum is nested inside an anyOf, so the schema adds little prose. The description says the filter is optional, implying null means all currencies, but does not clarify what the filter actually constrains (vendor rows vs payments) given the currency-matching rule above.

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 states the resource (vendor) and the exact measures returned (billed, paid, open balance), which is specific enough to distinguish it from a generic query tool. It does not, however, explicitly differentiate itself from run_sql, the closest sibling for ad-hoc queries.

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?

'Optionally filtered by currency' and the note about wrong-currency payments imply the reconciliation use case, but there is no explicit statement of when to choose this over run_sql or reconcile_ledger. Usage is inferable but not spelled out.

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