What is World Trimming in Minecraft? All You Need to Know.

World trimming is the process of deleting unused or unexplored chunks from your world to reduce file size and improve performance. Over time, as players explore your server, Minecraft generates thousands of chunks, many of which are barely visited and contain nothing but generated terrain.

By trimming these unused chunks, you can shrink a 120 GB world down to 30 GB or even smaller, reducing lag, speeding up backups, and freeing up valuable storage space.

Why World Trimming Matters

File Size Reduction

Minecraft worlds grow exponentially as players explore:​

• Each chunk (16×16 blocks) takes up storage space, even if players never return​
• A well-explored survival server can easily reach 50-150 GB after months of activity​
• Pre-generated worlds can bloat to hundreds of GB before players even join​

World trimming can reduce file sizes by 80-99% depending on how much of your world is actually used.​

Real-world example: A server with 134 GB across 29,861 files was trimmed down to 27 GB and 9,734 files, which is a 79.7% reduction.​

Performance Improvement

Smaller worlds perform better:​

• Faster backups: Less data to compress and upload​
• Quicker world loading: Server startup times drop significantly​
• Reduced RAM usage: Fewer chunks to track in memory​
• Better chunk loading: Less disk I/O when players explore​

Trimming is especially valuable before major Minecraft updates as you can delete distant, unused chunks and regenerate them with new biomes and features when the update drops.

Easier World Management

A trimmed world is easier to work with:​

• Faster downloads: Transfer your world to local editing tools in minutes instead of hours​
• More frequent backups: Smaller worlds back up faster, allowing more frequent safety snapshots​
• Lower storage costs: If your hosting plan charges per GB, trimming saves money

How World Trimming Works

World trimming identifies and deletes chunks based on criteria like:

Unexplored Chunks

Chunks that were generated but never visited by players. These contain only terrain generation with no player-placed blocks or modifications.​

Low-Activity Chunks

Chunks visited briefly but containing minimal player activity. No builds, no chests, no signs. These are often corridors players ran through once and never returned to.​

Invalid Chunks

Corrupted or incomplete chunks that failed to generate properly. These serve no purpose and can be safely deleted.​

After deletion, if players venture into trimmed areas again, Minecraft will regenerate fresh chunks using the current world seed.​

Tools for World Trimming

MCASelector (Recommended)

MCASelector is the most popular graphical tool for world trimming:​

• Visual chunk map showing inhabited time (how long players spent in each chunk)​
• Select and delete specific regions or mass-delete by criteria
• Works offline on downloaded worlds​
• Supports all three dimensions (Overworld, Nether, End)

How to use:

1. Download MCA Selector from mcaselector.​
2. Open your world folder in the tool
3. Use filters to highlight unused chunks (e.g., inhabited time < 1 minute)
4. Select and delete unwanted regions
5. Save and re-upload your trimmed world​

For large worlds (100+ GB), you may need to download the world in sections or use MCA Selector's headless mode on the server directly.​

WorldBorder Plugin

WorldBorder is a server-side plugin that can trim chunks beyond a specified border:​

/wb set 5000    # Set a 5000-block radius border
/wb trim        # Delete all chunks outside the border

Advantages:

• No need to download the world as it trims directly on the server​
• Perfect for setting permanent world boundaries​

Disadvantages:

• Can only trim by radius, not by chunk activity​
• Takes a long time on large worlds (hours to days)​

Minecraft World Trimmer (Command-Line)

A newer command-line tool for advanced users:​

minecraft_world_trimmer write ~/.minecraft/saves/MyWorld

Features:

• Parallel processing using all CPU threads for speed​
• Deletes unexplored and invalid chunks automatically​
• Improves compression on remaining chunks​
• Works on Linux servers without GUI​

Performance: Achieved 98.9% size reduction on a pre-generated world with minimal exploration.​

Amulet Editor

Amulet is another graphical world editor that supports chunk deletion:

• Select chunks manually or by filters
• Delete selected or unselected chunks
• Works on both Java and Bedrock worlds

Best Practices for World Trimming

Always Backup First

World trimming is destructive and irreversible. If you delete the wrong chunks, your only option is restoring from backup.

Backup checklist:

• Create a full world backup before trimming
• Test the backup by loading it to confirm it works​
• Store the backup separately from your server​

Trim Before Major Updates

Deleting distant chunks before updates like 1.21 Tricky Trials lets you regenerate them with new features:​

• Trim chunks 5,000+ blocks from spawn
• When the update releases, players exploring those areas will find new biomes, structures, and blocks

Set World Borders First

Before trimming, set a world border to prevent chunks from regenerating outside your desired play area:​

/worldborder set 10000

This keeps your world size manageable long-term​

Trim Dimensions Separately

Don't forget to trim the Nether and the End:

• Nether highways often extend thousands of blocks with minimal activity in between
• The End is frequently abandoned after the dragon fight. You can reset it entirely

Resetting the End is especially popular on servers to let players fight the dragon multiple times.​

When Not to Trim

Avoid trimming if:

• Players have hidden bases in distant chunks that look "unexplored"
• Your server advertises infinite exploration​
• You're running an anarchy server where preserving history matters

World trimming is essential maintenance for long-running Minecraft servers. By deleting unused and unexplored chunks, you can reduce world size by 80%+ while improving performance, speeding up backups, and preparing for major updates.

Tools like MCA Selector, WorldBorder, and Minecraft World Trimmer make the process straightforward, just remember to back up first and double-check your selections before deleting.