Mojang

Username To Uuid

username_to_uuid

Read-onlyIdempotent

Resolve a Minecraft username to its current Mojang UUID; returns the canonical UUID string used to identify the account.

Example tool call

This call uses example arguments supplied in the tool’s input schema.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {
      "username": "Notch"
    },
    "name": "username_to_uuid"
  }
}

Input Schema

Name	Required	Description	Default
`username`	Yes

Output Schema

Name	Required	Description	Default
`id`	Yes	UUID of the player
`name`	Yes	Current username of the player

Schema Changelog

Changes observed during successful MCP inspections.

Changed2 schema fields changedJun 7, 2026

addedInput schema / examples

Added value: +[
+  {
+    "username": "Notch"
+  },
+  {
+    "username": "steve"
+  }
+]

changedOutput schema / (root)

Previous value: -nullNew value: +{
+  "properties": {
+    "id": {
+      "description": "UUID of the player",
+      "type": "string"
+    },
+    "name": {
+      "description": "Current username of the player",
+      "type": "string"
+    }
+  },
+  "required": [
+    "id",
+    "name"
+  ],
+  "type": "object"
+}

First observedMay 20, 2026

TDQS

A4.1/5.0

Behavior4/5

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

Annotations already declare read-only, open-world, idempotent, and non-destructive behavior. The description adds valuable behavioral context by specifying the result is the 'current' and 'canonical' UUID string, which goes beyond the annotations.

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 a single, front-loaded sentence that immediately states the action and result. The second clause adds useful return semantics without unnecessary filler.

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 single-parameter read-only tool with an output schema, the description is largely complete. It omits edge cases like unknown usernames or case sensitivity, but given the low complexity and strong annotations, it is sufficient.

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

Parameters2/5

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

With a single 'username' parameter and 0% schema description coverage, the description only reiterates that it is a Minecraft username. It does not add format, case-sensitivity, or validation details, so it fails to compensate for the schema's lack of information.

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 uses a specific verb ('Resolve') with a clear resource ('Minecraft username') and result ('current Mojang UUID'), making the tool's purpose immediately obvious. The word 'current' differentiates it from sibling tools like username_to_uuid_at.

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 implies usage for resolving the current UUID, which provides clear context and distinguishes it from historical lookups. However, it does not explicitly name alternatives or state when not to use this tool.

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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