themesReturn the complete list of LEGO themes from Rebrickable (e.g. Star Wars, Technic, City). Returns theme id, name, and parent_id. Use to get valid theme_id values for filtering sets.
| Name | Required | Description | Default |
|---|---|---|---|
No arguments | |||
| Name | Required | Description | Default |
|---|---|---|---|
| next | No | URL to next page | |
| count | No | Total number of themes | |
| results | No | Array of theme 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 themes",
+ "type": "number"
+ },
+ "next": {
+ "description": "URL to next page",
+ "type": [
+ "string",
+ "null"
+ ]
+ },
+ "previous": {
+ "description": "URL to previous page",
+ "type": [
+ "string",
+ "null"
+ ]
+ },
+ "results": {
+ "description": "Array of theme objects",
+ "items": {
+ "properties": {
+ "id": {
+ "description": "Theme ID",
+ "type": "number"
+ },
+ "name": {
+ "description": "Theme name",
+ "type": "string"
+ },
+ "parent_id": {
+ "description": "Parent theme ID",
+ "type": [
+ "number",
+ "null"
+ ]
+ }
+ },
+ "type": "object"
+ },
+ "type": "array"
+ }
+ },
+ "type": "object"
+}Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already provide readOnlyHint, idempotentHint, and destructiveHint, so the description adds minimal new behavioral info beyond stating it returns the complete list. No contradictions.
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, front-loaded with the main action, and no extraneous information.
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?
For a zero-parameter tool with annotations and a described output, the description is complete. It explains the purpose, return fields, and usage context.
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?
There are zero parameters and 100% schema coverage, so baseline is 4. The description does not need to add parameter semantics.
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 uses specific verbs ('Return') and resource ('complete list of LEGO themes'). It provides examples and states the return fields (id, name, parent_id). It distinguishes from sibling tools like 'sets' by explaining its use for filtering.
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 states when to use the tool: 'Use to get valid theme_id values for filtering `sets`.' This gives clear context, though it could explicitly mention when not to use it or alternatives.
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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