Firefly III MCP Server

Create Firefly III Tag

firefly_create_tag

Create tags to label and categorize transactions in Firefly III, enabling organized financial tracking and structured expense management.

Instructions

Create a new tag for labeling transactions.

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": {
      "tag": "<tag>"
    },
    "name": "firefly_create_tag"
  }
}

Input Schema

Name	Required	Description	Default
`tag`	Yes	Tag name
`description`	No	Tag description

Schema Changelog

Changes observed during successful MCP inspections.

First observedv1.0.1Apr 7, 2026

TDQS

B3.2/5.0

Behavior3/5

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

Annotations declare readOnlyHint=false and destructiveHint=false, establishing this as a safe write operation. The description adds valuable context that tags are specifically for 'labeling transactions.' However, it fails to address idempotency behavior (idempotentHint=false implies duplicates may be created) or error conditions.

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?

Single sentence that is front-loaded with the action. Efficient and free of fluff, though perhaps too terse given the lack of usage guidelines or behavioral details.

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?

Adequate for a simple two-parameter creation tool with good schema coverage. Missing guidance on handling duplicate tag creation (given idempotentHint=false) and lacks return value documentation, though no output schema exists to require it.

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% with clear descriptions ('Tag name', 'Tag description'). The description does not add parameter semantics beyond the schema, but with full coverage, no additional compensation is required.

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?

Clearly states the verb (Create), resource (tag), and scope (for labeling transactions). However, it does not explicitly differentiate from sibling tools like firefly_create_category, which also organizes transactions.

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?

Provides no guidance on when to use this tool versus alternatives (e.g., categories vs. tags), prerequisites, or when to use firefly_update_tag instead. Completely silent on usage context.

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