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kern MCP server · D · ToolBench

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kern

github.com/jpoindexter/kern

MCP server — design system enforcement tools and resources for AI coding assistants

2026-07-28+STDIO6 tools

54/100

Definition Quality67

Protocol Readiness42

Supportability40

Spec posture

Inferred effective spec 2026-07-28+·current baseline 2026-07-28

Static source inference · medium confidence

Current-spec patterns detected

Summary

KERN MCP Server presents a domain-specific design system enforcement tool with moderate definition quality. All 6 tools are explicitly registered with descriptions and input schemas. Tool naming follows verb_noun convention (kern_*) and is domain-appropriate. However, descriptions lack LLM-optimized context about WHEN to use each tool relative to others, parameter descriptions are minimal or absent in several tools, and output schemas are not documented. Error handling guidance is absent. The server addresses a focused use case (design system validation for AI coding), which aids clarity, but lacks the depth expected of production-grade MCP servers.

Tools (6)

kern_checkread onlysource verified72/100

Validate code against design system rules. Returns violations with line numbers and auto-fix suggestions. Use to verify your code follows the design system before finishing.

kern_componentread onlysource verified62/100

Get the full spec for a specific component: import path, variants, props, example code, and rules. Use when you need details about how to use a particular component.

kern_patternread onlysource verified62/100

Get a specific UI composition pattern with full code template and layout structure. Use when building a page section and you need the exact code pattern to follow.

kern_suggestread onlysource verified68/100

Search for components and patterns that match a UI task. Use after kern_system to find specific patterns for what you're building. Returns ranked matches with code templates.

kern_systemread onlysource verified60/100

Get the complete design system. Call this FIRST before writing any UI code. Returns all tokens, rules, components, patterns, and usage instructions in one response.

kern_tokensread onlysource verified77/100

Get design tokens for a specific category. Returns valid values, forbidden patterns, and Tailwind class mappings. Use when you need the exact token values for colors, spacing, typography, or sizing.

Issues (6)

CRITICALtool ↗

Output schemas completely undocumented across all 6 tools. LLM cannot anticipate response structure, forcing trial-and-error usage and increasing hallucination risk.

kern_systemkern_suggestkern_componentkern_tokenskern_patternkern_check

HIGHconstrained-input ↗

No enum constraints for discoverable resources (valid component names, pattern names). LLM must guess or call kern_system first, increasing round-trips and context waste.

kern_componentkern_pattern

HIGHrecovery-guide ↗

kern_check lacks error handling guidance. No categorization of validation failures (retryable, user-fixable, fatal). No guidance on what to do when a violation is found.

kern_check

MEDIUMtool-description ↗

Descriptions contain example values (component names, pattern names, query strings) which LLMs tend to reuse literally. Example patterns should be formalized as enums or discoverable via a dedicated tool.

Recommendations

Add explicit output schema documentation for each tool. Document the structure of tokens, rules, components, violations, and suggestions. Include field names, types, and whether lists are paginated or capped.
Convert component and pattern name parameters to enums. If the list is large, add a dedicated 'list_components' or 'list_patterns' tool so LLM can discover valid values before calling kern_component or kern_pattern.
Enhance kern_check to return structured violation objects with: violation type, severity (error|warning), line number, column, rule name, explanation, and suggested fix. Add error handling guidance: 'If code is malformed, return a parse error with character position.'
Remove example values from descriptions and formalize them as enums or discovery tools. Change kern_suggest description from including examples to: 'Query string describing the UI feature (e.g., form layout, data display, navigation).' Move examples to a discoverable list or patterns catalog.
Add cross-tool chaining guidance. In kern_system description, add: 'Returns available components and patterns. Pass component or pattern names to kern_component or kern_pattern for details.' In kern_component/kern_pattern, add: 'Call kern_system first to discover available names.'
Document result limits. If kern_suggest returns a ranked list, specify: 'Returns up to 20 ranked matches. Use pagination if more results needed.' If kern_system returns large payloads, specify: 'Returns complete design system; may be large. Consider using kern_component or kern_tokens for targeted queries.'

Score history

Overall score trend

↓ 6 points across a rubric change (v1 → v2)

54/100

Scored	Grade	Overall	Spec posture	Rubric
2026-09-22	D	54	2026-07-28+	v2
2026-03-09	C	60	-	v1