Axiom for Minecraft: what it is and when to use it

What it is

Axiom is a Fabric mod for Java Edition that turns Creative mode into a world editor with real-time previews. Builder Mode adds tools such as clone, stack, extrude and symmetry to normal Creative. Editor Mode, opened with Right Shift, has a camera like 3D software and selection, painting, drawing, heightmap and manipulation tools.

It imports .schem and .schematic files, exports schematics and structure NBT, and saves its own .bp blueprints. On a multiplayer server it needs the Axiom Paper plugin and permission to use it.

A slice of the terrain Axiom is made for: a hill, a cliff and tilted rock layers, shaped and painted by eye.Drawn by BlockLab

What makers use it for

Terraform: sculpt mountains, cliffs and rock, with heightmap tools inspired by World Machine.
Paint and replace blocks over an area, with tool masks to limit what a tool touches.
Import a schematic, such as one exported from VoxelVision or BlockLab's Gradient page, preview it and place it.
Save builds as blueprints with tags and thumbnails, and reuse them in other worlds.

A large tree inside a translucent selection box in the middle of a brick town square, with a small tool bar and the Move tool name at the bottom of the screen. — In Builder Mode you stay in the normal game view and use tools such as Move on a selection, here a tree lifted as one piece.Screenshot: Axiom, from its Modrinth page

When to pick it

You build terrain, organic shapes or large structures by eye and want to see the result as you work.
You build in single player, on a localhost server or on a plot server, without making money from it: no restrictions apply.
You are fine with Fabric.

When another tool fits better

You want typed commands you can repeat or script: WorldEdit.
You use Forge or NeoForge: Axiom is a Fabric mod and Modrinth lists no other loader.
You make money from building (commissions, a monetized server): Axiom asks for a Commercial License. The price is not stated on the pages checked, so ask the developer.
You want to edit on a private multiplayer server without paying: you need a whitelist, requested on the Axiom Discord for a limited time and renewed when it ends.