# FModel: an Unreal Engine archive explorer for reading UE4 and UE5 packages > FModel is a C# desktop tool that opens Unreal Engine .pak archives and previews the assets inside them. It depends on CUE4Parse for parsing, ships under GPL-3.0, and needs a mapping file or AES key before encrypted games will open. **4sval/FModel** — Unreal Engine Archives Explorer - Repository: https://github.com/4sval/FModel - Website: https://fmodel.app - Stars: 3,193 · Forks: 472 - Language: C# - License: GPL-3.0 - Published: 2026-09-24 · Updated: 2026-09-24 · Language: en - Canonical page: https://hysenlabs.com/projects/4sval-fmodel ## What FModel is for, and who actually needs it Unreal Engine ships games as archives: .pak files holding the cooked assets, plus index structures that describe what is inside. Nothing in the engine's public tooling opens those archives for inspection outside the editor. FModel exists to fill that gap. It is a desktop explorer that reads the archive, lists the packages, and renders previews of what it finds, with conversion to usable formats as the follow-up step. The audience is narrow and specific. Modders who need a mesh, a texture, or a sound out of a shipped build. People documenting how a game is put together. Engineers who want to see the shape of UE4 or UE5 packaging in a real title rather than in documentation. The topics attached to the repository name the games people reach for it with: Fortnite, the GTA trilogy, PUBG, Valorant, MultiVersus, Stray, Palworld. That list is a description of user interest, not a guarantee that any particular title opens cleanly. If you are building a game, this is not your tool. If you are shipping one and want to inspect your own cooked output, the editor already does that. FModel's value is entirely in the case where you have archives and no editor to open them with. ## How FModel reads an archive: CUE4Parse underneath FModel is a front end. The parsing work is delegated to CUE4Parse, a separate library by FabianFG that is pulled into the repository as a submodule (the CUE4Parse entry sits alongside FModel/ at the top level, and .gitmodules is present). The README states plainly that FModel uses CUE4Parse as its core parsing library and that this provides support for the latest UE4 and UE5 archive formats. That split matters when something goes wrong. If a game's archive format is not understood, the failure surfaces in the parsing library, not in the UI. The release cadence reflects this: FModel publishes dated releases such as aug-2026 and dec-2025, and the parser underneath moves on its own schedule. A format added to CUE4Parse is only usable in FModel once the submodule is bumped and a build is cut. The data flow is conventional for this class of tool. You point FModel at a directory of archives, it builds a tree of the packages inside, and selecting a node asks the parser to deserialize that package. Previews are rendered from the deserialized data, and export writes it back out in a different format. The repository topics list OpenGL among them, which is consistent with the preview layer being GPU-backed rather than a set of static thumbnails. ## Installing FModel and opening your first archive The README does not carry install steps inline. It points to a wiki page, Installing FModel, and the release badge links to fmodel.app/download. That is the authoritative path: take the build from the download page or the GitHub release, not from a mirror. The wiki page is where the platform-specific instructions live, and it is the page to read before anything else. Once installed, the first real task is registering a game. In the UI you add an archive directory, and FModel scans it. The directory you want is the one holding the .pak files, typically under the game's Content/Paks folder. After the scan completes, the directory appears in the explorer and its packages can be browsed. The two blockers new users hit are both configuration, not installation. The first is the mapping file. Unreal Engine builds can strip the names that describe the structure of objects inside a package, leaving the data readable but unlabelled. FModel accepts a mapping file to restore those names, and the related searches show people looking for exactly that ("fmodel mapping file"). The second is encryption. Some titles encrypt their archives, and FModel needs the AES key for them. Without the key, the archive opens as ciphertext and nothing useful comes out. If a game is not encrypted and not name-stripped, adding the directory is the whole setup. If it is either, you supply the mapping file or the AES key before the tree is useful. The README does not document a rollback path for a bad mapping file; removing it and rescanning is the obvious move, but that is inference rather than a documented procedure. ## The mapping file and the AES key are where most setups stall These two inputs deserve their own treatment because they are the difference between a working session and a directory of unreadable blobs, and neither is bundled. A mapping file is a separate artifact describing the internal names of objects in a build. It is produced outside FModel, usually by tooling that runs against the game. FModel consumes it. The practical consequence is that mapping files are version-specific: a mapping generated for one build of a game will not necessarily describe another, and a mismatched mapping produces wrong names rather than an error. If the tree looks plausible but the names are nonsense, the mapping is the first thing to check. An AES key is a single secret, and it is per-title. FModel uses it to decrypt archives that the developer encrypted at packaging time. The related searches ("fmodel aes key") show this is a common entry point, and it is also the point where the tool's documentation is thinnest: the README does not explain how to obtain a key, and it should not, because that is not something the project can supply. You either have the key or the title does not open. Both inputs are configuration you carry between sessions. Neither is something FModel derives for you. ## What FModel will not do for you The most honest limitation is legal and practical rather than technical. Extracting and redistributing assets from a commercial game is governed by that game's terms, not by FModel's licence. The GPL-3.0 on the tool says nothing about the content you pull out of a title with it. Nothing in the README addresses this, and it is the single most common misunderstanding around tools of this kind. The second limitation is coverage. FModel supports the archive formats that CUE4Parse supports. A title using a format the parser has not caught up with, or a heavily customised build, will not open. The topics list names specific games, which can read as a compatibility guarantee; it is not one. It is a list of what users talk about. The third is that this is a viewer, not a pipeline. There is no headless batch mode described in the README, no documented scripting interface, and no mention of a CLI. If your workflow is "extract forty thousand textures overnight and feed them into a build step", FModel is the wrong shape of tool, and you would be better served by driving CUE4Parse directly in C#, which is the same library without the UI wrapped around it. Finally, the preview layer is a viewer. Whether a given asset type renders correctly depends on the format and the version, and the README makes no claim about which types preview well. ## FModel against driving CUE4Parse yourself The real alternative is not another GUI. It is CUE4Parse, the same library FModel is built on, used directly from C#. The difference is the layer you own. FModel gives you a finished application: archive registration, a package tree, previews, and export, all wired together, with the cost that you work at the speed of its release cycle and inside its UI. CUE4Parse gives you the parsing primitives and nothing else. You write the traversal, decide the output format, and can run it unattended. You also take on the maintenance of tracking format changes yourself. The choice follows from volume and repetition. Opening a handful of packages to look at something is a GUI job, and FModel is the shorter path. Processing an entire game's archive set on a schedule is a library job. FModel's own architecture makes this the natural comparison, since the submodule boundary is exactly where the split falls. If you find yourself wanting to automate what you are doing in FModel, that is the signal to move down a layer rather than to look for a second GUI tool. ## Licence, release cadence, and what upgrades cost FModel is licensed under GPL-3. The README links the licence file and a separate NOTICE file listing the licences of third-party libraries used. That NOTICE file is worth reading before you build anything on top of the project, because the dependency set includes the parsing library and the rendering stack, and their terms are not the same as FModel's. This is a description of what the repository contains, not legal advice; if GPL-3.0 obligations matter to your distribution, that is a question for someone qualified to answer it. On cadence: the last push to the repository was on 2026-09-23, and the most recent release is aug-2026, published on 2026-08-02. Before that, dec-2025 on 2025-12-19, and 4.4.4.0 on 2024-10-20. The gap between the 2024 and 2025 releases and the tighter spacing since is visible in the release list. The upgrade cost is mostly the mapping file. A new FModel build may parse a game's archives differently, and if the game has also been updated, the mapping you were using may no longer describe it. Budget for re-obtaining mappings alongside tool upgrades rather than treating them as independent. The default branch is dev, so the stable artifact is the tagged release, not a build from the branch head. ## Conclusion FModel is for people who need to look inside Unreal Engine packages: modders, asset rippers, and engineers studying how a shipped UE4 or UE5 title is assembled. It is not for anyone who wants a redistributable asset pipeline, because GPL-3.0 applies to the tool and its derivatives, and third-party library terms are listed separately in NOTICE. Before relying on it for a specific game, verify three things: that the game's archives open at all, that you have the mapping file or AES key the encrypted case needs, and that the export format you need exists in the version you installed. The dev branch is where work lands; the August 2026 release is the stable artifact to start from. ## FAQ ### What is FModel used for? FModel is an archive explorer for Unreal Engine games. It opens UE4 and UE5 .pak archives, lets you browse the packages inside, previews their contents, and converts them to other formats. ### Is FModel free to use? Yes. FModel is licensed under GPL-3, and the repository includes a NOTICE file listing the licences of the third-party libraries it uses. The project also accepts sponsorship through a donate link on fmodel.app. ### Is the FModel app safe? The README does not make a safety claim. The reliable check is provenance: take builds from the fmodel.app download page or the GitHub release rather than a mirror, since those are the sources the repository itself links to. ### How do I install FModel? The README does not list install steps inline. It points to the Installing FModel page on the project wiki, and the release badge links to fmodel.app/download. ### How do I use FModel? You add the directory holding the game's .pak files to FModel, let it scan, then browse the resulting package tree. Encrypted or name-stripped titles need an AES key or a mapping file before the tree is useful. ### What is FModel? It is an Unreal Engine archives explorer written in C#, using CUE4Parse as its core parsing library for UE4 and UE5 archive formats. It is licensed under GPL-3. ## Sources - [4sval/FModel on GitHub](https://github.com/4sval/FModel) - [License: GPL-3.0](https://github.com/4sval/FModel/blob/dev/LICENSE) - [Project website](https://fmodel.app) - [README](https://github.com/4sval/FModel/blob/dev/README.md) - [Releases](https://github.com/4sval/FModel/releases) --- Hysen Labs editorial analysis, written from the project's own repository and release notes. Cite the canonical page: https://hysenlabs.com/projects/4sval-fmodel