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The Flags Generator creates optimized startup scripts for your Minecraft server with carefully tuned JVM arguments. Access it at birdflop.com/resources/flags.

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Features

  • Support for multiple flag collections (Aikar’s, MeowIce’s, Benchmarked, and more)
  • Cross-platform script generation (Linux, Windows, macOS, Pterodactyl)
  • Multiple server types (Paper, Purpur, Velocity, Waterfall)
  • Automatic memory overhead calculation
  • Environment variables support
  • Auto-restart configuration
  • GUI disable option
  • GraalVM optimization flags

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Getting Started

1

Configure Basic Settings

  1. Enter your server JAR filename (e.g., paper.jar, purpur.jar)
  2. Select your operating system/environment
  3. Choose your server software type
  4. Set the amount of RAM to allocate
2

Choose Flag Collection

Select a flag set based on your needs:
  • Aikar’s Flags: Proven, widely-used flags
  • MeowIce’s Flags: Modern optimization flags
  • Benchmarked: Scientifically tested flags
  • hilltty’s Flags: Alternative optimization approach
  • Obydux’s Flags: GraalVM-specific optimizations
  • Etil’s Flags: Balanced performance flags
3

Configure Options

Enable optional features:
  • No GUI mode (recommended for servers)
  • Use variables for easier editing
  • Auto-restart on crash
  • Calculate overhead (recommended)
4

Copy and Use

Copy the generated script from the output box and save it as:
  • Linux/macOS: start.sh
  • Windows: start.bat
  • Pterodactyl: Paste into startup command field

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Configuration Options

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File Name

The name of your server JAR file. Common examples:
  • paper.jar
  • purpur.jar
  • velocity.jar
  • server.jar
The generator automatically appends .jar if you forget it.

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Environment

Choose your server’s operating system:

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Linux

Generates a bash script (start.sh) for Linux servers. Most common for dedicated servers and VPS.

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Windows

Generates a batch script (start.bat) for Windows servers.

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macOS

Generates a bash script optimized for macOS systems.

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Pterodactyl

Generates a command suitable for the Pterodactyl panel’s startup field.

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Command

Generates a raw Java command without script wrapper.

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Software

Select your server software:
  • Paper: Most popular performance-focused server
  • Purpur: Paper fork with additional features
  • Velocity: Modern proxy server
  • Waterfall: Paper-based BungeeCord fork
Some options (like GUI disable) are automatically hidden for software that doesn’t support them.

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Memory Allocation

Amount of RAM to allocate to your server (in GiB):
  • Minimum: 1 GB (only for test/development servers)
  • Recommended: 4-8 GB for small-medium servers
  • Large Servers: 12-16+ GB for many players
Don’t allocate all available RAM. Leave at least 1-2 GB for the operating system.

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Calculate Overhead

Enables automatic memory overhead calculation to prevent out-of-memory errors. Formula: (11x ÷ 12) - 1200MB where x is allocated RAM Example: With 6GB allocated, the JVM receives ~4.3GB, leaving room for overhead.
Always enable this option unless you have a specific reason not to. It prevents crashes from memory issues.

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Flag Collections Explained

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Aikar’s Flags

Aikar’s Flags are the most widely-used JVM flags in the Minecraft community. Best for: General use, proven stability, wide compatibility Key optimizations:
  • G1GC garbage collector tuning
  • Optimized heap sizing
  • Reduced GC pause times
  • Memory allocation efficiency

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MeowIce’s Flags

MeowIce’s Flags provide modern optimizations for current Java versions. Best for: Modern servers, Java 17+ Key optimizations:
  • Updated GC tuning for Java 17+
  • Reduced memory overhead
  • Improved throughput
  • Lower latency

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Benchmarked Flags

Benchmarked flags are scientifically tested through extensive benchmarks. Best for: Maximum performance, willing to test Key optimizations:
  • Empirically tested settings
  • Multiple configurations for different scenarios
  • Regular updates based on new tests

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hilltty’s Flags

hilltty’s Flags offer an alternative optimization approach. Best for: Alternative to mainstream flags

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Obydux’s Flags

Obydux’s Flags are specifically designed for GraalVM. Best for: Servers running GraalVM JDK Requirements: Must use GraalVM, not standard OpenJDK

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Etil’s Flags

Balanced performance flags suitable for most servers. Best for: General use, balanced approach

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Advanced Options

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No GUI

Disables the default server GUI window. Benefits:
  • Slightly reduced memory usage
  • Better for headless servers
  • Required for some server environments
When to use: Always enable for production servers

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Use Variables

Uses environment variables for memory, filename, and other settings. Benefits:
  • Easier to modify settings
  • More maintainable scripts
  • Better for version control
Example output: 
MEMORY=6G
FILE=paper.jar
java -Xms$MEMORY -Xmx$MEMORY -jar $FILE

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Auto-restart

Automatically restarts the server if it stops or crashes. Benefits:
  • Automatic recovery from crashes
  • Continuous uptime
  • Useful for automatic updates
When to use: Production servers, unattended servers
Make sure you can manually stop the auto-restart loop (usually Ctrl+C).

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Extra Flags

Platform-specific optimizations that appear based on your selections:

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Modern Vectors

Enables SIMD operations for optimized map rendering on Pufferfish and forks. Requirements: Pufferfish-based server (Purpur, etc.)

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Benchmarked (GraalVM)

Additional flags for Benchmarked collection on GraalVM. Requirements: GraalVM JDK + Benchmarked flags selected

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MeowIce’s Flags (GraalVM)

GraalVM-specific optimizations for MeowIce’s flags. Requirements: GraalVM JDK + MeowIce’s flags selected

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Platform-Specific Instructions

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Linux

  1. Save the generated script as start.sh
  2. Make it executable: 
    chmod +x start.sh
  3. Run the script: 
    ./start.sh

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Windows

  1. Save the generated script as start.bat
  2. Double-click to run, or use command prompt: 
    start.bat

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macOS

  1. Save the generated script as start.sh
  2. Make it executable: 
    chmod +x start.sh
  3. Run the script: 
    ./start.sh

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Pterodactyl

  1. Copy the generated command
  2. In your Pterodactyl panel, go to Startup
  3. Paste into the Startup Command field
  4. Restart your server

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Optimization Tips

Start Conservative: Begin with Aikar’s flags, then experiment with others if needed.
Monitor Performance: Use Spark or Timings to measure impact.
Match RAM to Players: ~1GB per 10 players is a rough guideline, but varies by plugins and world size.

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Testing Different Flags

To compare flag collections:
  1. Generate a baseline profile with current flags
  2. Switch to new flags and restart
  3. Generate another profile under similar conditions
  4. Compare TPS, MSPT, and GC activity

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When to Change Flags

  • Server TPS consistently below 20
  • High garbage collection pause times
  • Out of memory errors
  • Upgrading Java versions
  • Changing server software

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Common Issues

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Out of Memory Errors

Solution: Enable “Calculate Overhead” or allocate more RAM

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Server Won’t Start

Check:
  • Java version compatibility (Java 17+ required for modern servers)
  • Correct JAR filename
  • Sufficient RAM available
  • File permissions (Linux/macOS)

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Poor Performance Despite Flags

Remember: Flags help, but can’t fix:
  • Inefficient plugins
  • World issues (excessive entities, etc.)
  • Insufficient hardware
  • Poor server configuration
Use the Spark Analyzer to identify the actual bottleneck.

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Java Version Recommendations

Minecraft VersionRecommended Java
1.20.5+Java 21
1.18 - 1.20.4Java 17
1.17Java 16
1.16 and belowJava 11
Flags are optimized for these Java versions. Using older or newer Java may reduce effectiveness.

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GraalVM Benefits

GraalVM is an alternative JDK that can provide better performance: Pros:
  • Potentially higher TPS
  • Better JIT compilation
  • Lower latency
  • Specialized optimizations
Cons:
  • Less tested in production
  • May have compatibility issues
  • Requires specific flags
When to use: Experimental servers, performance testing, specific compatibility needs

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