colorsReturn the complete list of LEGO colors from Rebrickable with color id, name, RGB hex code, and is_trans flag. Use to get valid color_id values for filtering parts.
| Name | Required | Description | Default |
|---|---|---|---|
No arguments | |||
| Name | Required | Description | Default |
|---|---|---|---|
| next | No | URL to next page | |
| count | No | Total number of colors | |
| results | No | Array of color objects | |
| previous | No | URL to previous page |
Changes observed during successful MCP inspections.
Input schema / examplesAdded value: +[
+ {}
+]Output schema / (root)Previous value: -nullNew value: +{
+ "properties": {
+ "count": {
+ "description": "Total number of colors",
+ "type": "number"
+ },
+ "next": {
+ "description": "URL to next page",
+ "type": [
+ "string",
+ "null"
+ ]
+ },
+ "previous": {
+ "description": "URL to previous page",
+ "type": [
+ "string",
+ "null"
+ ]
+ },
+ "results": {
+ "description": "Array of color objects",
+ "items": {
+ "properties": {
+ "id": {
+ "description": "Color ID",
+ "type": "number"
+ },
+ "is_trans": {
+ "description": "Whether color is transparent",
+ "type": "boolean"
+ },
+ "name": {
+ "description": "Color name",
+ "type": "string"
+ },
+ "rgb": {
+ "description": "RGB hex code",
+ "type": [
+ "string",
+ "null"
+ ]
+ }
+ },
+ "type": "object"
+ },
+ "type": "array"
+ }
+ },
+ "type": "object"
+}Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare readOnlyHint and idempotentHint, so the tool is safe. The description adds that it returns a list with specific fields, which is helpful but not critical 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.
Is the description appropriately sized, front-loaded, and free of redundancy?
Two sentences, no waste. Front-loads the action and output, then states the use case.
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?
Given no parameters and an output schema present, the description is complete. It tells what the tool returns and why to use it, meeting all needs for a simple list tool.
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?
The tool has no parameters, so the description adds meaning by explaining what the output contains. The schema provides no details, so the description fully compensates.
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 it returns a complete list of LEGO colors with specific fields (color id, name, RGB hex, is_trans). It also explains the purpose: to get valid color_id values for filtering parts, distinguishing it from sibling tools like 'parts'.
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 description explicitly says 'Use to get valid color_id values for filtering `parts`,' providing clear context for when to use it. It does not mention when not to use, but the intended use is unambiguous.
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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