username_to_uuid_atResolve a Minecraft username to the UUID it was assigned at a given Unix epoch timestamp (seconds); useful for historical name lookups.
| Name | Required | Description | Default |
|---|---|---|---|
| username | Yes | ||
| timestamp | No |
| Name | Required | Description | Default |
|---|---|---|---|
| id | Yes | UUID of the player at the given timestamp | |
| name | Yes | Username of the player at the given timestamp |
Changes observed during successful MCP inspections.
Input schema / examplesAdded value: +[
+ {
+ "timestamp": 1609459200,
+ "username": "Notch"
+ },
+ {
+ "username": "steve"
+ }
+]Output schema / (root)Previous value: -nullNew value: +{
+ "properties": {
+ "id": {
+ "description": "UUID of the player at the given timestamp",
+ "type": "string"
+ },
+ "name": {
+ "description": "Username of the player at the given timestamp",
+ "type": "string"
+ }
+ },
+ "required": [
+ "id",
+ "name"
+ ],
+ "type": "object"
+}Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare readOnlyHint, idempotentHint, and non-destructive behavior, lowering the burden. The description adds the unit of timestamp (seconds) and the historical aspect, but it does not disclose behaviors like error handling or what happens if the username is unknown. This is acceptable given the strong annotations but not rich behavioral detail.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.
Is the description appropriately sized, front-loaded, and free of redundancy?
The description is a single, front-loaded sentence that conveys the essential action and use case without any redundant wording or fluff.
Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.
Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?
As a simple read-only lookup with two parameters and an output schema, the description is largely sufficient. It covers the core 'at timestamp' nuance and the historical use case. It could be more complete by explicitly referencing the sibling tool for current UUIDs, but this is minor given the low complexity.
Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.
Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?
Schema coverage is 0%, so the description must add meaning to the parameters. It explains that 'username' is a Minecraft username and 'timestamp' is in Unix epoch seconds, which is helpful. However, it does not clarify that timestamp is optional (per schema) or what default behavior occurs without it, leaving a gap for the 0%-coverage schema.
Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.
Does the description clearly state what the tool does and how it differs from similar tools?
The description clearly states the tool resolves a Minecraft username to a UUID 'at a given Unix epoch timestamp', which is a specific verb+resource+scope. It distinguishes itself from the sibling 'username_to_uuid' (which likely returns the current UUID) by emphasizing historical lookups.
Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.
Does the description explain when to use this tool, when not to, or what alternatives exist?
The phrase 'useful for historical name lookups' implies when to use this tool, but it does not explicitly name any alternative or when not to use it. Clear context is provided, but exclusions are missing, making it slightly less explicit than the ideal.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.