Performance Smell Detection

This helps you spot Java performance smells like regex compilation in loops, string concatenation inefficiencies, and boxing overhead, but it's opinionated about modern Java realities. The author correctly notes that string concatenation with + is fine in Java 9+ for simple cases thanks to invokedynamic, and that streams are often acceptable except in tight loops with huge datasets. The guidance on regex pre-compilation and StringBuilder in loops remains valid. What I appreciate is the "measure first" philosophy throughout, acknowledging that readability often trumps micro-optimizations and that JVMs have gotten really good at optimization. It explicitly scopes itself to code-level issues and punts JPA/database problems to the jpa-patterns skill, which is the right call.

skills.sh installs: 341
GitHub stars: 771
last updated: Feb 8, 2026

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Install

$ npx -y skills add decebals/claude-code-java --skill performance-smell-detection --agent claude-code

Installs into .claude/skills of the current project.

Files

Performance Smell Detection Skill

Identify potential code-level performance issues in Java code.

Philosophy

"Premature optimization is the root of all evil" - Donald Knuth

This skill helps you notice potential performance smells, not blindly "fix" them. Modern JVMs (Java 21/25) are highly optimized. Always:

Measure first - Use JMH, profilers, or production metrics
Focus on hot paths - 90% of time spent in 10% of code
Consider readability - Clear code often matters more than micro-optimizations

When to Use

Reviewing performance-critical code paths
Investigating measured performance issues
Learning about Java performance patterns
Code review with performance awareness

Scope

This skill: Code-level performance (streams, collections, objects) For database: Use jpa-patterns skill (N+1, lazy loading, pagination) For architecture: Use architecture-review skill