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justmytwospence

ynab-mcp

Create Category Group

create_category_group

Create a new category group in a YNAB budget to organize spending categories for better financial management.

Instructions

[1 API call] Create a new category group in a budget

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
budget_idNoBudget ID or 'last-used'last-used
nameYesCategory group name (max 50 characters)

Implementation Reference

  • Registration and handler implementation for the create_category_group tool.
    server.registerTool("create_category_group", {
      title: "Create Category Group",
      description: "[1 API call] Create a new category group in a budget",
      inputSchema: {
        budget_id: z.string().default("last-used").describe("Budget ID or 'last-used'"),
        name: z.string().max(50).describe("Category group name (max 50 characters)"),
      },
      annotations: { readOnlyHint: false },
    }, async ({ budget_id, name }) => {
      try {
        const response = await getClient().categories.createCategoryGroup(budget_id, {
          category_group: { name },
        });
        const g = response.data.category_group;
        return textResult(`Created category group "${g.name}"\nID: ${g.id}`);
      } catch (e: any) {
        return errorResult(e.message);
      }
    });
Behavior3/5

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

The annotation 'readOnlyHint: false' already indicates this is a write operation, which the description confirms with 'Create'. The description adds minimal behavioral context with '[1 API call]', hinting at a single network request, but doesn't disclose permissions, side effects, error conditions, or response format. It doesn't contradict annotations but adds limited value beyond them.

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?

The description is extremely concise—two brief phrases with zero wasted words. It front-loads the key information ('Create a new category group') and includes a useful technical note ('[1 API call]'). Every element serves a purpose without redundancy.

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

Completeness3/5

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

For a creation tool with no output schema and minimal annotations, the description is incomplete. It lacks details on what the tool returns (e.g., the created category group object), error handling, or dependencies. However, the simple parameter set (2 params) and clear purpose partially compensate, making it minimally viable but with gaps.

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?

With 100% schema description coverage, the input schema fully documents both parameters (budget_id and name). The description adds no parameter-specific information beyond what's in the schema, such as examples or constraints. The baseline score of 3 reflects adequate coverage via the schema alone.

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 clearly states the specific action ('Create a new category group') and specifies the resource context ('in a budget'), which distinguishes it from sibling tools like 'create_category' or 'update_category_group'. It uses a precise verb+resource combination that leaves no ambiguity about the tool's function.

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

Usage Guidelines2/5

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

The description provides no guidance on when to use this tool versus alternatives like 'update_category_group' or 'merge_category'. It doesn't mention prerequisites (e.g., needing an existing budget), exclusions, or typical use cases. The agent must infer usage from the tool name alone.

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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