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YNAB MCP Server

by calebl
OverviewSchemaSourceRelated ServersDiscussionsAdmin
TypeScript
Remote

Update Category Budget

ynab_update_category_budget
Idempotent

Update a category's budgeted amount for any month, enabling fund allocation or transfers between categories.

Instructions

Updates the budgeted amount for a category in a specific month. Use this to allocate funds to categories or move money between categories.

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
monthYesThe plan month in ISO format (e.g. 2024-01-01). Must be the first day of the month.
planIdNoThe plan ID (optional, defaults to YNAB_PLAN_ID; budgetId is a deprecated alias)
budgetIdNoDeprecated alias of planId (still accepted)
budgetedYesThe amount to budget in dollars (e.g. 500.00). This sets the total budgeted amount, not an increment.
categoryIdYesThe ID of the category to update

Schema Changelog

Changes observed during successful MCP inspections.

  1. Changed6 schema fields changedv0.3.0
    • removedInput schema / additionalProperties
      Removed value: -false
    • addedInput schema / properties / budgetId / anyOf
      Added value: +[
+  {
+    "description": "Deprecated alias of planId (still accepted)",
+    "type": "string"
+  },
+  {
+    "type": "null"
+  }
+]
    • changedInput schema / properties / budgetId / description
      Previous value: -"The ID of the budget (optional, defaults to YNAB_BUDGET_ID environment variable)"New value: +"Deprecated alias of planId (still accepted)"
    • removedInput schema / properties / budgetId / type
      Removed value: -"string"
    • changedInput schema / properties / month / description
      Previous value: -"The budget month in ISO format (e.g. 2024-01-01). Must be the first day of the month."New value: +"The plan month in ISO format (e.g. 2024-01-01). Must be the first day of the month."
    • addedInput schema / properties / planId
      Added value: +{
+  "anyOf": [
+    {
+      "description": "The plan ID (optional, defaults to YNAB_PLAN_ID; budgetId is a deprecated alias)",
+      "type": "string"
+    },
+    {
+      "type": "null"
+    }
+  ],
+  "description": "The plan ID (optional, defaults to YNAB_PLAN_ID; budgetId is a deprecated alias)"
+}
  2. Addedv1.0.0

TDQS

A3.5/5.0
Behavior3/5

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

The description states that the tool mutates budgeted amounts, which is consistent with readOnlyHint=false and idempotentHint=true and does not contradict the annotations. It adds little beyond the core operation, such as effects on available amounts, permissions, or return behavior, but the annotations already cover the basic safety profile.

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 only two sentences and front-loads the core operation. It is concise and easy to scan, though the second sentence's overlap with ynab_move_money makes it slightly less crisp than it could be.

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

Completeness4/5

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

For a simple update operation with fully documented parameters and informative annotations, the description is sufficiently complete for an agent to select and invoke the tool. The main missing element is explicit guidance about when to prefer ynab_move_money, but this is a minor gap given the straightforward purpose.

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

Parameters3/5

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

Schema description coverage is 100%, so all five parameters are already well documented, including the critical fact that budgeted sets the total amount rather than an increment. The tool description adds no parameter-specific meaning beyond the general allocation/move-money framing, so the baseline of 3 applies.

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

Purpose4/5

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

The description names a specific verb and object: it updates the budgeted amount for a category in a specific month. It is clear about the core operation, but it does not explicitly distinguish itself from sibling tools like ynab_move_money, and the phrase 'move money between categories' blurs that boundary.

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

Usage Guidelines3/5

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

The description gives a direct use case: 'Use this to allocate funds to categories or move money between categories.' However, it does not mention alternatives or exclusions, which matters because ynab_move_money exists as a sibling and may be the more appropriate tool for cross-category moves.

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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