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a1athrop

YNAB MCP Server

by a1athrop

create_transaction

Add a new transaction to your YNAB budget by specifying account, date, amount, payee, category, and optional details like memo or split transactions.

Instructions

Create a new transaction.

Args: account_id: The account UUID to create the transaction in. date: Transaction date in YYYY-MM-DD format. amount: Amount in milliunits (negative for outflows, positive for inflows). Example: -50000 = -$50.00 outflow, 150000 = $150.00 inflow. payee_name: Name of payee (creates new payee if doesn't exist). Use this OR payee_id. payee_id: UUID of existing payee. Use this OR payee_name. category_id: UUID of the budget category. Omit when using subtransactions (each sub has its own). memo: Transaction memo. cleared: Cleared status: "cleared", "uncleared", or "reconciled". Defaults to "cleared". approved: Whether the transaction is approved. Defaults to True. flag_color: Optional flag: red, orange, yellow, green, blue, purple. subtransactions: Array of subtransaction objects for split transactions. Each item: {"amount": int, "category_id": "uuid", "memo": "text", "payee_id": "uuid", "payee_name": "text"}. Only amount and category_id are required per sub. The sub amounts must sum to the parent amount. When using subtransactions, omit category_id on the parent (it becomes a split). budget_id: Budget ID (uses default if omitted).

Returns: Created transaction details with id, date, amount, payee, category, and subtransactions.

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
account_idYes
dateYes
amountYes
payee_nameNo
payee_idNo
category_idNo
memoNo
clearedNocleared
approvedNo
flag_colorNo
subtransactionsNo
budget_idNo

Output Schema

TableJSON Schema
NameRequiredDescriptionDefault
resultYes
Behavior4/5

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

With no annotations provided, the description carries the full burden of behavioral disclosure. It effectively describes key behaviors: it's a creation tool (implying mutation), specifies default values (e.g., cleared defaults to 'cleared', approved defaults to True), explains conditional logic (payee_name vs. payee_id, category_id omission with subtransactions), and details constraints (subtransactions amounts must sum to parent amount). It could improve by mentioning authentication needs or error handling, but it's quite comprehensive.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness4/5

Is the description appropriately sized, front-loaded, and free of redundancy?

The description is well-structured with clear sections (Args, Returns) and uses bullet-like formatting for readability. Most sentences earn their place by providing essential information, but it could be more front-loaded—the detailed parameter explanations are lengthy, though necessary given the 0% schema coverage. A brief summary upfront might enhance conciseness.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness5/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

Given the complexity (12 parameters, no annotations, 0% schema coverage) and the presence of an output schema (implied by 'Returns' section), the description is highly complete. It thoroughly explains all input parameters, their interactions, defaults, and constraints, and summarizes the return values. This provides enough context for an agent to use the tool effectively without relying on structured fields.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters5/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is 0%, so the description must fully compensate. It excels by providing detailed semantics for all 12 parameters: explains formats (e.g., date in YYYY-MM-DD, amount in milliunits with sign conventions), clarifies usage (e.g., payee_name creates new payee if missing, payee_id for existing), defines enums (e.g., cleared status options, flag colors), describes complex structures (subtransactions array with required fields and summation rule), and notes defaults and optionality. This adds significant value beyond the bare schema.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

The description starts with a clear, specific verb ('Create') and resource ('a new transaction'), immediately stating what the tool does. It distinguishes from siblings like 'create_transactions_bulk' (single vs. bulk creation), 'delete_transaction' (creation vs. deletion), and 'update_transaction' (creation vs. modification), making the purpose unambiguous.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines4/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

The description provides clear context for usage through parameter explanations (e.g., 'Use this OR payee_id' for payee_name, 'Omit when using subtransactions' for category_id, 'uses default if omitted' for budget_id). However, it lacks explicit guidance on when to choose this tool over alternatives like 'create_transactions_bulk' or 'update_transaction', which would be needed for a perfect score.

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

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