bethkit

⚠️ Beta — APIs may change before the first stable release.

A fast, zero-copy Rust library for reading and writing Bethesda game plugin and archive files. Callable from any language via a stable C ABI (bethkit-ffi).

What it does

• Zero-copy plugin parsing — plugins are memory-mapped; records borrow bytes directly from the mapping without extra allocations
• Record schema — SchemaRegistry::sse() covers all 126 SSE record types; SchemaRegistry::fo4() covers all 137 FO4 types. RecordView decodes subrecords into typed FieldValue variants: integers, floats, FormIDs, enums with resolved names, bit-flags, structs, and arrays. All schema data is &'static — zero heap allocation at runtime. Placement records (REFR, ACHR) are not schema-covered; complex multi-variant fields fall back to a raw byte slice.
• BSA / BA2 archives — read and extract all major formats (BSA TES3/TES4/FO3/SSE, BA2 GNRL/DX10); write new archives with parallel compression
• Streaming record replace — PluginPatcher rewrites arbitrary records in-place; cost is O(edits), not O(plugin size)
• Writer — build new plugins from scratch; eslify existing plugins; set the LOCALIZED flag
• Localized strings — read, edit, and write .STRINGS / .DLSTRINGS / .ILSTRINGS files; apply translation patches without touching the plugin binary
• Load-order utilities — LoadOrder, GlobalFormId, PluginCache for winning-override lookups and EditorID search across multiple plugins
• C ABI — bethkit-ffi exposes ~110 extern "C" functions with a pre-generated bethkit.h included in the repository

Crates

• bethkit-io — memory-mapped I/O, SliceCursor, zlib/LZ4 decompression
• bethkit-core — ESP/ESL/ESM parser, writer, patcher, string tables, record schema
• bethkit-bsa — BSA and BA2 archive reader and writer
• bethkit-ffi — C ABI wrapper and bethkit.h header

Supported games

The parser, writer, and patcher work for all TES4-era games. The current focus is completing full schema coverage for Skyrim SE (126 types) and Fallout 4 (137 types). Schemas for other games (Oblivion, Fallout 3/NV, Starfield, Morrowind) are planned for later milestones.

Documentation

• Quick Start
• Reading Plugins
• Writing & Patching Plugins
• BSA / BA2 Archives
• Record Schema
• Localized Strings
• Load Order & FormID Resolution
• C ABI / Language Bindings
• Architecture

Compared to alternatives

	bethkit	sse-plugin-interface	xEdit	Mutagen
Language	Rust + C ABI	Python	Delphi	C#
License	Apache-2.0	MIT	MPL 2.0	GPL-3.0
Embeddable library	✅	✅	❌ GUI/CLI	✅
Schema-typed record access	✅ runtime	❌	✅ full	✅ compile-time
BSA / BA2 write	✅	❌	✅	read only
Streaming record replace	✅	❌	✅	❌
Conflict detection	❌	❌	✅	❌
C ABI for cross-language use	✅	❌	❌	❌

bethkit's niche is a fast, embeddable, language-agnostic library for direct binary access. xEdit is the authoritative reference tool with full conflict detection, a GUI, and schema definitions for every field across every game. Mutagen offers compile-time-typed record schemas for C# patcher authors, with the Synthesis framework on top; its GPL-3.0 licence restricts embedding in proprietary tools. sse-plugin-interface is minimal by design — purpose-built for SSE-Auto-Translator.

Status

Milestone	Status
Parser + writer + tests (SSE)	✅
String tables	✅
Streaming rewrite (PluginPatcher)	✅
BSA / BA2 reader + writer	✅
PluginCache (winning override, EditorID lookup)	✅
Record schema — SSE (126 types registered, deep coverage WIP)	⚠️ WIP
Record schema — FO4 (137 types registered, deep coverage WIP)	⚠️ WIP
C ABI (bethkit-ffi)	✅
Python bindings — bethkit.py	✅
Record schema — other games	🗓️ Planned

License

Apache-2.0