# Mojang/DataFixerUpper

A set of utilities designed for incremental building, merging and optimization of data transformations.

Repository: https://github.com/Mojang/DataFixerUpper
Canonical: https://ross.abutalabs.com/products/datafixerupper
Language: Java
License: MIT
License Family: permissive
Topics: mojang-active
Last push: 2026-05-05T09:20:32+00:00

## Health v2 (maintenance only)
Score: 59/100 (v2, computed 2026-09-02T17:46:02.011165+00:00)
- activity 80, release rhythm 8, longevity 100
- inputs: {"age_days": 2988, "days_push": 120, "days_rel": null, "gap_med": null, "n_releases_24m": 0}
- flags: none
- formula: round(0.45*activity + 0.35*rhythm + 0.20*longevity); archived -> min(score, 10)

## Adoption (not part of the score)
Stars 1309, forks 152 (observed 2026-08-28T04:04:19.382542+00:00)

## What it is
DataFixerUpper is a Java library from Mojang for incrementally building, merging, and optimizing data transformations between schema versions. It was created to convert Minecraft: Java Edition game data between game versions.

## Use cases
- migrate saved game data between schema versions
- build incremental data transformation pipelines
- upgrade JSON or NBT structures when a schema changes
- compose and optimize chains of rewrite rules on typed data
- define versioned schemas and fixes for evolving data formats

## When to choose
- you need to migrate structured data across many successive schema versions
- you want composable, optimizable rewrite rules rather than ad-hoc migration scripts
- you are working in the JVM ecosystem, e.g. modding or tooling for Minecraft

## When to avoid
- you only need a one-off simple data conversion
- you are not on the JVM and cannot use a Java library
- you need ETL across external systems rather than in-process data structure upgrades

## Facets
- artifact type: library
- maturity: active
- function: serialization, etl, developer-tools
- domain: gaming-tools, developer-tools
- platform: jvm
- tags: data-migration, schema-evolution, datafix, minecraft, version-upgrade, data-engineering

## Member repositories
- Mojang/DataFixerUpper (main) score 59

## Provenance
- Observed fields: from GitHub, fetched 2026-08-28T04:04:19.382542+00:00.
- Health v2: computed from the inputs above; adoption is never an input.
- Inferred fields (summary, facets, guidance): AI-extracted, prompt v1, taxonomy v1, on 2026-08-30T04:49:57.868540+00:00, confidence not recorded.
  - readme: https://github.com/Mojang/DataFixerUpper (fetched 2026-08-28T04:04:19.382542+00:00, sha afac8c3cb9c8)
- Data as of 2026-08-30T08:39:29.467469+00:00.