What is the ESP file format?
.esp files are plugin files used across Bethesda's Elder Scrolls and Fallout series, covering games from Morrowind and Oblivion through Skyrim, Fallout 3, Fallout: New Vegas, and Fallout 4 built on the Creation Engine.
.esp files are used for storing mods for the original game, which can include:
- custom dialog lines,
- custom and/or new items,
- custom gameplay configs,
- new engine settings,
- additional locations.
Files with the .esp extension contain plugin data that depends on one or more master .esm files loaded before them. Mods are created by fans as a means of expanding or customizing gameplay, updating original designs, or adding additional elements enriching user experience, for example adding new questlines or references to earlier titles in the series.
Bethesda Softworks made authoring tools available to the public. Fallout 3 and Fallout: New Vegas include a program called G.E.C.K. (Garden of Eden Creation Kit), while Elder Scrolls and later Fallout titles use the Creation Kit. By using these programs users can create and edit .esp game files and alter their contents. When loaded by the game, .esp plugins override or add to data already defined in the master .esm files; this layering mechanism allows custom settings to be applied on top of the vanilla game without permanently altering it. Community tools such as xEdit (also known as SSEEdit or FO4Edit) let modders inspect and resolve conflicts between multiple plugins. For smaller mods, a lighter variant called .esl can be used instead; it uses the same underlying format but is flagged to occupy a shared load-order slot, bypassing the 255-plugin limit.
Security & safety
RISK: MEDIUMAn .esp is data, not an executable, so it can't run code by itself - but mods are community-made and can break saves, cause crashes, or be bundled with malicious loose files/scripts. Download only from reputable sources (Nexus Mods, Bethesda.net), keep a clean load order, sort with LOOT, and clean dirty edits in xEdit. Beware archives that include unexpected executables alongside the .esp, and never trust an '.esp' that is actually .esp.exe.
Format details
in a nutshell- Adobe Photoshop EPS (Encapsulated PostScript) - Some pipelines write .esp for EPS vector/raster artwork; unrelated to game mods (see the .eps format).
- Email Service Provider / Eclipse project files - Various apps have used .esp for config or project data; niche and unrelated to Bethesda plugins.
Programs that open ESP files
Windows5 apps
Creation Kit
Free Load the .esp as the active plugin to author/edit game content (per-game official editor).
Vortex (Nexus mod manager)
Free Install the mod; Vortex deploys the .esp and manages load order so the game loads it.
Mod Organizer 2
Open-source Install/enable the plugin in a virtual file system; sort load order with LOOT inside MO2.
xEdit (SSEEdit / FO4Edit / TES5Edit)
Open-source Open the .esp to inspect/edit records, clean dirty edits, resolve conflicts, or flag it as .esl.
Fallout (legacy game)
Paid The plugin is loaded by the Bethesda game it targets at launch, not opened standalone. 
Linux1 app
Mod Organizer 2 / Vortex (via Proton/Steam)
Open-source Run the Windows mod manager under Proton to manage .esp plugins for the game's Linux/Steam Deck install. Technical details
deep spec| Format type | Binary record/subrecord plugin (Creation Engine) |
| Byte order | Little-endian |
| File signature | `TES4` at offset 0 (Oblivion and later); `TES3` for Morrowind-era `.esp` files |
| String encoding | Null-terminated Windows-1252 in early games (Oblivion, Fallout 3/NV); null-terminated UTF-8 from Skyrim Special Edition onwards |
| Compression | Optional per-record zlib compression applied to individual game-object records (Skyrim and later) |
| Typical file size | 1 KB to 250 MB (single-item tweaks to large total-conversion mods) |
| Structure | TES4 header record followed by typed GRUP record groups; each group contains typed game-object records and subrecords |
| FormID space | 24-bit object ID per record; the high byte encodes the plugin's load-order index (0x00-0xFE for full plugins) |
| Load-order cap | 255 full plugins (`.esp` + `.esm`) per game session; light `.esl` plugins share a separate extended pool of up to 4096 slots |
| Form version | Integer in the TES4 header distinguishes game target (43 for Skyrim LE, 44 for Skyrim SE, separate values for Fallout 4) |
| Master dependency | Plugin lists required `.esm` master files in its TES4 header; the engine enforces load order and will refuse to load without them |
| Plugin vs. master flag | A single flag in the TES4 record header distinguishes `.esp` (plugin) from `.esm` (master); the binary layout is otherwise identical |
| Platform support | Windows (primary); Xbox and PlayStation via Bethesda.net console mod support |
| Associated asset archives | Meshes, textures, and sounds are stored separately in [`.bsa`](/format/bsa) or [`.ba2`](/format/ba2) archives, not inside the `.esp` |
| Toolchain | Official Creation Kit (Skyrim, Fallout 4) and G.E.C.K. (Fallout 3/New Vegas); community tools include xEdit (SSEEdit, FO4Edit) and Mod Organizer 2 |
| Released | 2002 (The Elder Scrolls III: Morrowind, NetImmerse/Gamebryo TES3 record format) |
| Latest version | Creation Engine TES4/TES5/FO4 plugin format (Starfield, 2023) |
| Specification | en.uesp.net |
ESP conversions
Community Q&A
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