YNAB MCP Server

Update Category Budget

ynab_update_category_budget

Idempotent

Sets the total budgeted amount for one category in a specific month (not an increment). To move money between categories, use ynab_move_money instead.

Instructions

Sets the total budgeted amount for one category in a specific month (not an increment). To move money between categories, use ynab_move_money instead.

Tool call template

Replace each placeholder with a value matching the input schema. Only required parameters are included; add optional parameters as needed.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {
      "month": "<month>",
      "categoryId": "<categoryId>",
      "budgeted": "<budgeted>"
    },
    "name": "ynab_update_category_budget"
  }
}

Input Schema

Name	Required	Description
`month`	Yes	The plan month in ISO format (e.g. 2024-01-01). Must be the first day of the month.
`planId`	No	The plan ID (optional, defaults to YNAB_PLAN_ID; budgetId is a deprecated alias)
`budgetId`	No	Deprecated alias of planId (still accepted)
`budgeted`	Yes	The amount to budget in dollars (e.g. 500.00). This sets the total budgeted amount, not an increment.
`categoryId`	Yes	The ID of the category to update

Schema Changelog

Changes observed during successful MCP inspections.

Changed6 schema fields changedv0.3.0Sep 22, 2026

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)"
+}

Addedv1.0.0Jan 2, 2026

TDQS

A4.4/5.0

Behavior4/5

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

Annotations already declare readOnlyHint=false, idempotentHint=true, and destructiveHint=false, so the safety profile is carried structurally. The description adds the most consequential behavioral fact – that this overwrites the total rather than adding to it – which explains the idempotency. It does not cover auth requirements or failure behavior, keeping it short of a 5.

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

Conciseness5/5

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

Two sentences, zero waste, with the highest-risk semantic caveat front-loaded and the alternative routing delegated to sentence two.

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 mutation tool with annotations covering safety, full schema coverage, and no output schema, the description supplies the two facts an agent most needs: absolute-set semantics and sibling routing. Minor omission – no mention of what the write affects or returns – but nothing essential is missing for correct invocation.

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%, including the fact that 'budgeted' sets the total rather than an increment, so the description's '(not an increment)' clause largely restates the schema. Baseline 3 is appropriate since the schema does the heavy lifting on month format, planId defaults, and deprecation.

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?

States a specific verb (sets), resource (budgeted amount), and precise scope (one category, one month), and explicitly disambiguates the semantics with '(not an increment)'. An agent can distinguish it from ynab_move_money without opening either schema.

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

Usage Guidelines5/5

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

Names the alternative tool (ynab_move_money) and the condition that selects it (moving money between categories). Combined with the explicit 'not an increment' exclusion, both the when-to-use and when-not-to-use cases are covered.

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