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Magic MCP UI builder by 21st.dev - A Model Context Protocol server for building and refining React UI components with AI assistance
Four tools with visible schemas and descriptions, but significant quality gaps. Tool names lack action verbs (21st_magic_component_builder vs create_component). Descriptions are verbose (200-300+ chars) and include implementation guidance rather than LLM-optimized selection criteria. Parameter descriptions exist but lack constraints, formats, and validation rules. No output schemas documented. Error handling absent. Schemas use Zod but lack enum constraints and type specificity. No tool annotations (readOnlyHint, destructiveHint). Tools appear to call external APIs (21st.dev) but no error recovery guidance provided.
Use this tool when the user requests a new UI component—e.g., mentions /ui, /21 /21st, or asks for a button, input, dialog, table, form, banner, card, or other React component. This tool ONLY returns the text snippet for that UI component. After calling this tool, you must edit or add files to integrate the snippet into the codebase.
Use this tool when the user wants to see component, get inspiration, or /21st fetch data and previews from 21st.dev. This tool returns the JSON data of matching components without generating new code. This tool ONLY returns the text snippet for that UI component. After calling this tool, you must edit or add files to integrate the snippet into the codebase.
Use this tool when the user requests to re-design/refine/improve current UI component with /ui or /21 commands, or when context is about improving, or refining UI for a React component or molecule (NOT for big pages). This tool improves UI of components and returns redesigned version of the component and instructions on how to implement it.
Search and return logos in specified format (JSX, TSX, SVG). Supports single and multiple logo searches with category filtering. Can return logos in different themes (light/dark) if available. When to use this tool: 1. When user types "/logo" command (e.g., "/logo GitHub") 2. When user asks to add a company logo that's not in the local project Example queries: - Single company: ["discord"] - Multiple companies: ["discord", "github", "slack"] - Specific brand: ["microsoft office"] - Command style: "/logo GitHub" -> ["github"] - Request style: "Add Discord logo to the project" -> ["discord"] Format options: - TSX: Returns TypeScript React component - JSX: Returns JavaScript React component - SVG: Returns raw SVG markup Each result includes: - Component name (e.g., DiscordIcon) - Component code - Import instructions
Tool names lack action verbs. '21st_magic_component_builder', '21st_magic_component_inspiration', '21st_magic_component_refiner' do not start with clear verbs (create_, fetch_, refine_). LLMs cannot infer intent from names alone.
No output schemas documented. Tools return text snippets or JSON but LLMs cannot plan downstream calls or extract structured data. Responses lack field definitions.
Parameter descriptions lack constraints. 'searchQuery' has no length limit, format, or example. 'absolutePathToCurrentFile' has no validation rules. LLMs will pass invalid values.
| Scored | Grade | Overall | Spec posture | Rubric |
|---|---|---|---|---|
| 2026-09-23 | F | 48 | 2026-07-28+ | v2 |
No error handling or recovery guidance. Tools call external APIs (21st.dev) but no documentation of failure modes, timeouts, or what LLM should do if API is unavailable.
Tool descriptions are implementation-focused, not LLM-selection-focused. They explain what the tool does AFTER calling it ('After calling this tool, you must edit or add files') rather than WHEN to call it. Descriptions exceed 200 chars baseline.