record_payment

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

With no annotations, the description carries the full burden and does substantial work: it discloses that this mutates local state (principal reduction), that no external money movement occurs, and that retries should reuse an idempotency key. It leaves gaps on permissions and whether an entry can be reversed or corrected afterward.

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 tight sentences with no filler, and the core behavior plus the safety-relevant scope limit are front-loaded. The interest clause is dense and slightly opaque without domain context, but 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?

An output schema exists, so return values need not be explained. For a six-parameter mutation tool with zero annotation coverage, the description covers the key surprises (no external transfer, idempotency, interest semantics) but omits edge behavior such as overpayment, validation failures, and reversibility.

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 0% across six parameters, so the description must compensate. It adds real meaning for the two least-obvious ones (interest as a replacement for estimated newly assessed finance charges, and idempotency_key for retries) but says nothing about date, note, amount, or debt_id semantics.

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 ('Write an actual payment journal entry') plus the resulting effect ('reduce local principal'), and immediately delimits scope with 'No external money transfer'. That scoping clause separates it cleanly from sibling tools like simulate_plan and compare_strategies without needing to name them.

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?

Usage context is implied by the contrast between 'actual' payment and the simulate/compare siblings, and the retry instruction ('reuse an idempotency key on retries') is actionable. However, it never explicitly says when to prefer this over simulate_plan or what preconditions must hold (e.g. debt must exist locally).

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