Rebrickable

Set Parts

set_parts

Idempotent

Fetch the full parts list for a LEGO set by set_num from Rebrickable. Returns each part's part_num, name, color, quantity, and image URL.

Input Schema

Name	Required	Description	Default
`set_num`	Yes

Output Schema

Name	Required	Description
`next`	No	URL to next page
`count`	No	Total number of parts
`results`	No	Array of part objects in set
`previous`	No	URL to previous page

Schema Changelog

Changes observed during successful MCP inspections.

Changed2 schema fields changedMay 22, 2026

addedInput schema / examples

Added value: +[
+  {
+    "set_num": "75368-1"
+  }
+]

changedOutput schema / (root)

Previous value: -nullNew value: +{
+  "properties": {
+    "count": {
+      "description": "Total number of parts",
+      "type": "number"
+    },
+    "next": {
+      "description": "URL to next page",
+      "type": [
+        "string",
+        "null"
+      ]
+    },
+    "previous": {
+      "description": "URL to previous page",
+      "type": [
+        "string",
+        "null"
+      ]
+    },
+    "results": {
+      "description": "Array of part objects in set",
+      "items": {
+        "properties": {
+          "color": {
+            "properties": {
+              "id": {
+                "description": "Color ID",
+                "type": "number"
+              },
+              "name": {
+                "description": "Color name",
+                "type": "string"
+              },
+              "rgb": {
+                "description": "RGB hex code",
+                "type": "string"
+              }
+            },
+            "type": "object"
+          },
+          "id": {
+            "description": "Inventory ID",
+            "type": "number"
+          },
+          "is_spare": {
+            "description": "Whether this is a spare part",
+            "type": "boolean"
+          },
+          "part": {
+            "properties": {
+              "name": {
+                "description": "Part name",
+                "type": "string"
+              },
+              "part_cat_id": {
+                "description": "Part category ID",
+                "type": "number"
+              },
+              "part_num": {
+                "description": "Part number",
+                "type": "string"
+              }
+            },
+            "type": "object"
+          },
+          "quantity": {
+            "description": "Quantity of this part",
+            "type": "number"
+          }
+        },
+        "type": "object"
+      },
+      "type": "array"
+    }
+  },
+  "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 indicate idempotent and non-destructive behavior. The description adds value by specifying the returned fields (part_num, name, color, quantity, image URL), providing useful context beyond 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 clear sentence with no waste, front-loading the key action and resource.

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?

The tool is simple with one parameter and the description adequately explains output fields. With output schema present, the description covers enough for selection and invocation.

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?

Schema coverage is 0% and the description only mentions 'by set_num' without adding format details or examples. The schema has an example '75368-1' but the description does not reference it. Given the single parameter, more guidance would be helpful.

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 it fetches the full parts list for a LEGO set by set_num from Rebrickable, with specific verb and resource. It distinguishes from sibling tools like 'set_minifigs' which focus on minifigs.

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 implicitly guides when to use: when you need parts for a LEGO set. However, it does not explicitly mention alternatives or when not to use.

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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