Biblioteca

Turn a dimension's vertical space into a loop.

"La biblioteca es ilimitada y periódica." — Jorge Luis Borges, Ficciones (1944)

Travel past the top of the world and continue from the bottom, or fall through the bottom and arrive at the top. Biblioteca makes the two sides neighbours, with continuous movement and a repeating view of the world above and below you.

The place where the top and bottom meet is the boundary. In a normal Overworld, it joins y = 320 to y = -64.

Looping is optional for each dimension and works with existing worlds. The mod keeps normal world generation and adds no blocks, items or world types. Existing terrain, including bedrock, stays in place, so solid blocks can still obstruct a passage through the boundary.

What you can do

• Enable looping independently for the Overworld, Nether, End or a modded dimension.
• Build and interact across the boundary, with block and entity collisions in the right places.
• Use fluids, redstone, pistons and supported plant growth across the top and bottom.
• Decorate and spawn across the boundary: paintings and item frames hang across the seam at any height, and a spawn egg puts the mob on the block you clicked instead of inside it.
• See repeated terrain, nearby entities and block entities, periodic beacon beams and clouds.
• Fight mobs and trade with villagers on the other side: they see you, path to you, hit you and cross the boundary without a visible jump.
• See rain and snow across the boundary, with rain splashes, hot-surface smoke and impact sounds.
• Hear positional sounds and see effects from the other side, with matching sound subtitles.
• Track your crossings with Seam crossings in the vanilla statistics screen.

Requirements and installation

• Minecraft 26.3, using Fabric Loader 0.19.5 or newer.
• Fabric API for Minecraft 26.3.
• Java 25 or newer.

Install Fabric API and the normal Biblioteca JAR in the client's mods folder. Multiplayer servers also need Biblioteca and Fabric API; use matching Biblioteca versions on both sides.

Dedicated servers can use the -norender JAR. Clients need the normal JAR to see the looping world. Install only one Biblioteca JAR in each instance: both variants use the same mod ID.

Enable looping

For a new singleplayer world, open Create New World → More → Dimension Attributes. Choose the settings for the Overworld, Nether and End, press Done, and create the world.

For an existing world, a server or a modded dimension, use commands. Cheats or operator permission level 2 are required:

/biblioteca looping set minecraft:overworld true

Replace minecraft:overworld with the dimension ID you want, such as minecraft:the_nether, minecraft:the_end or an ID added by another mod. To turn looping off again:

/biblioteca looping set minecraft:overworld false

Dimension settings

All four settings default to false. The three additional attributes affect dimensions where Y-axis looping is enabled.

For No void fog and No sky light, false keeps the original effect and true disables it. The world-creation buttons show Keep fog / Disable fog and Keep skylight / Disable skylight to make the result clear. Keeping sky light does not add it to a dimension that normally has none.

Use true or false for <bool>. Run beacon, no_void_fog or no_sky_light without a value to see its current setting. These three commands act on the dimension you are standing in.

For example, to use beacons and hide void fog while keeping sky light:

/biblioteca beacon true
/biblioteca no_void_fog true
/biblioteca no_sky_light false

Settings are saved with the world and synchronized to connected players.

Transparency and performance

Biblioteca supports water, stained glass and other translucent terrain both with and without Improved Transparency, Minecraft's OIT option. The mod does not force that option on.

On newer GPUs that support OIT, we recommend enabling Improved Transparency for better performance. Find it under Options → Video Settings.

If OIT is unavailable, or you turn the option off, Biblioteca uses sorted transparency for the repeated terrain. You can switch it off on an OIT-capable GPU to compare the two paths. Sorting can cost more CPU time, and intersecting translucent faces can still show artifacts that OIT handles more accurately.

A high render distance shows more repeated terrain and increases rendering work. Very short dimensions can be more demanding because many copies fit in view. Reduce render distance if needed.

Seam preload (sections), also in Video Settings, ranges from 0 to 8. Higher values prepare more terrain across the boundary ahead of time and can reduce loading hitches, at the cost of extra work. The default is 0; each step adds 16 blocks of preload slack.

Existing worlds and upgrading

You can enable or disable looping in an existing world. It uses the dimension's existing height; it does not generate extra vertical terrain or duplicate your blocks and entities. Ordinary entities and block entities are shown at the copy nearest you.

In 0.67.0, the old void_fog and sky_light settings were renamed and inverted. To preserve their previous effects, use the opposite boolean with no_void_fog and no_sky_light. For example, keeping the old defaults requires setting both new attributes to true in each looping dimension. See the manual migration instructions for the complete command table.

Compatibility and feedback

Biblioteca changes Minecraft's world and renderer internals. Mods that replace the same systems may need compatibility work. Shader packs have not been comprehensively tested. The no-render variant is intended for servers and does not provide the visual loop on a client.

For a bug report, include your Minecraft/mod versions, other installed mods, the log and steps to reproduce it. For a rendering problem, also include your GPU, render distance, dimension height and whether Improved Transparency is enabled.

Source and developer documentation · Report an issue · Release history

Author: FrogBishop. Inspired by Jorge Luis Borges' The Library of Babel. Bug fixes and rendering work: DeepSeek-v4.1-flash, GPT-6-Astra. Licensed under GPLv3.