# Code Runner

> Run code snippets in 30+ programming languages including JavaScript, Python, TypeScript, Java, C, C++, Go, Rust, Ruby, PHP, and more. Use when the user wants to execute code, test algorithms, verify output, run scripts, or check code behavior. Supports both interpreted and compiled languages. Use when this capability is needed.

- Skill: `tomevault-io/code-runner` (Agent Skill, multi-file: 2 files)
- Install (CLI): `npx skillmds@latest add tomevault-io/code-runner`
- Raw SKILL.md: https://api.skillmd.com/api/skills/tomevault-io/code-runner/raw
- Safety review: pending (external: skill-scanner PASS, skillspector PASS)
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Coding & Dev Tools
- Author: tomevault-io (https://skillmd.com/u/tomevault-io)
- Updated: 2026-09-17
- Page: https://skillmd.com/skills/tomevault-io/code-runner

---


# Code Runner Skill

This skill enables you to run code snippets in multiple programming languages directly from the command line.

## When to Use This Skill

Use this skill when:
- The user wants to run or execute a code snippet
- Testing algorithm implementations or logic
- Verifying expected output of code
- Running quick scripts or one-liners
- Checking syntax or runtime behavior
- Demonstrating code functionality

## Supported Languages

The following languages are supported (requires the interpreter/compiler to be installed):

| Language | Command | File Extension |
|----------|---------|----------------|
| JavaScript | `node` | `.js` |
| TypeScript | `ts-node` | `.ts` |
| Python | `python` | `.py` |
| Java | `java` (compile & run) | `.java` |
| C | `gcc` (compile & run) | `.c` |
| C++ | `g++` (compile & run) | `.cpp` |
| Go | `go run` | `.go` |
| Rust | `rustc` (compile & run) | `.rs` |
| Ruby | `ruby` | `.rb` |
| PHP | `php` | `.php` |
| Perl | `perl` | `.pl` |
| Lua | `lua` | `.lua` |
| R | `Rscript` | `.r` |
| Swift | `swift` | `.swift` |
| Kotlin | `kotlin` | `.kts` |
| Scala | `scala` | `.scala` |
| Groovy | `groovy` | `.groovy` |
| Dart | `dart` | `.dart` |
| Julia | `julia` | `.jl` |
| Haskell | `runhaskell` | `.hs` |
| Clojure | `clojure` | `.clj` |
| F# | `dotnet fsi` | `.fsx` |
| C# | `dotnet script` | `.csx` |
| PowerShell | `pwsh` | `.ps1` |
| Bash | `bash` | `.sh` |
| Batch | `cmd /c` | `.bat` |
| CoffeeScript | `coffee` | `.coffee` |
| Crystal | `crystal` | `.cr` |
| Elixir | `elixir` | `.exs` |
| Nim | `nim compile --run` | `.nim` |
| OCaml | `ocaml` | `.ml` |
| Racket | `racket` | `.rkt` |
| Scheme | `scheme` | `.scm` |
| Lisp | `sbcl --script` | `.lisp` |

See [references/LANGUAGES.md](references/LANGUAGES.md) for detailed language configuration.

## How to Run Code

### Step 1: Identify the Language

Determine the programming language from:
- User's explicit request (e.g., "run this Python code")
- File extension if provided
- Code syntax patterns

### Step 2: Execute Using the Runner Script

**⚠️ Important for AI Agents**: Use stdin to avoid escaping issues with quotes, backslashes, and special characters.

**Recommended Method (stdin):**
```bash
echo "<code>" | node scripts/run-code.cjs <languageId>
```

**Alternative Method (CLI argument - for simple code only):**
```bash
node scripts/run-code.cjs <languageId> "<code>"
```

**Example - JavaScript:**
```bash
echo "console.log('Hello, World!')" | node scripts/run-code.cjs javascript
```

**Example - Python:**
```bash
echo "print('Hello, World!')" | node scripts/run-code.cjs python
```

**Example - Java (multi-line):**
```bash
echo "public class Test {
    public static void main(String[] args) {
        System.out.println(\"Hello from Java!\");
    }
}" | node scripts/run-code.cjs java
```

**Example - Multi-line code from variable:**
```bash
# In bash
CODE='import math
print("Pi:", math.pi)
print("Result:", math.factorial(5))'
echo "$CODE" | node scripts/run-code.cjs python

# In PowerShell (inline here-string)
@"
import math
print("Pi:", math.pi)
print("Result:", math.factorial(5))
"@ | node scripts/run-code.cjs python
```

### Step 3: Return Results

- Show the output (stdout) to the user
- If there are errors (stderr), explain what went wrong
- Suggest fixes for common errors

## Platform Notes

### Windows
- Use `cmd /c` for batch scripts
- PowerShell scripts require `pwsh` or `powershell`
- Path separators use backslash `\`

### macOS / Linux
- Bash scripts work natively
- Swift available on macOS
- Use `#!/usr/bin/env` shebang for portable scripts

## Error Handling

Common issues and solutions:

1. **Command not found**: The language interpreter is not installed or not in PATH
   - Suggest installing the required runtime
   - Provide installation instructions

2. **Syntax errors**: Code has syntax issues
   - Show the error message
   - Point to the line number if available

3. **Runtime errors**: Code runs but fails during execution
   - Display the stack trace
   - Explain the error type

4. **Timeout**: Code takes too long (default: 30 seconds)
   - Warn about infinite loops
   - Suggest optimizations

## Security Considerations

⚠️ **Important**: Running arbitrary code can be dangerous. Always:

1. Review the code before execution
2. Be cautious with code that:
   - Accesses the file system
   - Makes network requests
   - Executes system commands
   - Modifies environment variables
3. Consider running in a sandboxed environment for untrusted code

## Examples

### Example 1: Run a JavaScript calculation
```bash
echo "console.log(Array.from({length: 10}, (_, i) => i * i))" | node scripts/run-code.cjs javascript
```
Output: `[0, 1, 4, 9, 16, 25, 36, 49, 64, 81]`

### Example 2: Run Python with imports
```bash
echo "import math; print(math.factorial(10))" | node scripts/run-code.cjs python
```
Output: `3628800`

### Example 3: Test a Go function
```bash
echo 'package main; import "fmt"; func main() { fmt.Println("Hello from Go!") }' | node scripts/run-code.cjs go
```
Output: `Hello from Go!`

---
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<!-- tomevault:4.0:skill_md:2026-04-14 -->