Postings: add free posting

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

Annotations already declare idempotentHint=false, and the description reinforces this: 'Not idempotent: calling twice may create duplicates.' and 'Not idempotent, so a repeated call books the amount twice.' It adds context about attaching a receipt later via `postings_assign_receipt_to_free`, which is useful lifecycle information. No contradiction with annotations. The description provides practical behavioral implications beyond what annotations state.

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?

The description is well-structured with a clear warning header, then a purpose statement, usage guidance, and batch/non-idempotency notes. It is somewhat long but every sentence adds useful information—no filler. The most critical warnings (write, non-idempotent) are front-loaded, which is good for agent attention.

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?

The tool has an output schema, so return format is defined. The description covers what the tool does, when to use it, batch behavior, non-idempotency, and related tools for attaching receipts. It does not mention potential errors or authentication, but those are not expected given the output schema and annotations. Overall it is complete enough for an agent to call it correctly.

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 100% with each parameter described in the schema, so the description doesn't need to restate them. It does add meaning by explaining the concept of a 'free' posting (you name both sides yourself via `postingaccount_debit` and `postingaccount_credit`) and clarifies that the `free_postings` parameter is an array even for a single posting. This adds semantic value beyond the schema's basic field definitions.

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 clearly states that this tool adds free postings (debit/credit pairs not tied to a receipt or bank transaction) and explicitly distinguishes it from `postings_create_for_receipt` and `postings_create_for_transaction`. The verb 'add' plus the resource 'free posting' is specific, and it disambiguates against sibling tools.

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 explicit guidance on when to use it: 'Use to book a debit/credit pair that is not tied to an existing receipt or bank transaction, such as a manual accrual or a correction.' It also states alternatives: 'If the booking documents a receipt, use postings_create_for_receipt. If it settles a bank transaction, use postings_create_for_transaction.' This fully covers when and when-not, and names the alternative tools.

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