Anvil

Anvil is a plugin loader for Europa Universalis IV (Windows, Steam). It lets native plugins improve or extend the game without modifying eu4.exe.

Install guide, plugin catalog and docs for plugin authors: anvil.happydwarf.dev.

Status: Anvil 1.x with plugin API 2 — see Releases and CHANGELOG.md. Supported game build: EU4 1.37.5 (Steam, Windows 64-bit); on other builds only plugins that use no game addresses load. Design: docs/design.md. Plugin API 2: include/anvil/anvil_plugin.h (C) and include/anvil/anvil.hpp (C++20 wrapper); examples: examples/hello-c and examples/hello-cpp.

How it works (in short)

• Anvil ships as a version.dll placed next to eu4.exe. Windows loads it together with the game; it forwards every version.dll call to the system copy and, in addition, loads plugins.
• Plugins live in anvil/plugins/<plugin-id>/ (manifest + DLL). They can also come in EU4 mods, from the Steam Workshop or the local mod folder, as anvil/<plugin-id>/ in the mod. Such a plugin loads only while its mod is enabled in the playset and only after the player approves its exact files in the overlay or in AnvilManager.exe. An update waits for a new approval. Approvals are kept in anvil/trust.toml, and an approved plugin loads from Anvil's own copy in anvil/data/anvil/approved/.
• A plugin that uses game addresses declares them, for one EU4 build, in its symbols.toml; on another build it is skipped. Broken plugins, plugins written for an older plugin API or an empty plugins folder mean the game simply starts as usual. The manifest format is described in docs/design.md.
• Anvil ships the standard plugin anvil-game (anvil/plugins/anvil-game/): game readiness, a frame event, work on the main thread and game sessions (include/anvil/anvil_game.h). Plugins that change the simulation need it: in ironman and multiplayer games Anvil takes their changes out unless the player allows them in anvil/anvil.toml.
• Anvil also ships anvil-overlay (anvil/plugins/anvil-overlay/): in-game notices about plugins that were not loaded, the previous crash and safe mode, and a panel on Ctrl+Shift+F12 with the status, "disable at the next start", the crash report, the log and every plugin's settings. It draws on the game's Direct3D 9 renderer and stays off with OpenGL.
• Each start writes anvil/anvil.log: what was loaded, what was skipped and why.
• A crash writes a report to anvil/crashes/ (the last 10 are kept): where it happened and which plugins were involved, with each plugin's issues link. After two starts in a row that ended before the game was ready, the next start loads only Anvil's standard plugins (safe mode), and the overlay says why.

Install / uninstall

Download from the Releases page (the newest build is always at releases/latest). SHA256SUMS.txt there holds the checksums of the assets.

With Anvil Manager (AnvilManager.exe). Run it, and it finds the game through Steam (or lets you pick the folder that contains eu4.exe). "Install Anvil" copies version.dll, the standard plugins and the Manager into that folder; from then on, start the Manager there.

• It shows which plugins will load and why, and turns plugins on and off.
• It installs a plugin from its release zip after checking it against your eu4.exe, and edits plugin settings.
• On its Mods tab it approves and revokes plugins that come with enabled mods (Anvil 1.3 and later), checking that the mod still has the version shown.
• On its Benchmark tab (Anvil 1.5 and later) it measures how long the game takes to start without a plugin and with it, in a series of starts that quit by themselves, and shows the result with cold starts apart. The report is sent to the maintainers only when you click "Send" after seeing it, or copied; see docs/benchmark-privacy.md and the specification.
• It shows crash reports and the log, and starts the game through Steam.
• "Repair" puts back Anvil's own files.
• "Uninstall Anvil" removes version.dll, the standard plugins and the Manager, and keeps your plugins, their settings and anvil/anvil.toml. Tick "Also remove my plugins…" to remove the anvil folder too.
• To update Anvil, run the Manager of the newer release.
• While the game runs, the Manager only shows. It is not code-signed, so Windows SmartScreen may ask once ("More info" → "Run anyway").

By hand. Extract anvil-windows-x64.zip into the game folder (the archive has its own SHA256SUMS.txt for the extracted files). To uninstall, delete version.dll, AnvilManager.exe and the anvil folder.

eu4.exe is never changed, so Steam updates and "Verify integrity of game files" keep working. Without version.dll the game starts vanilla.

Plugins

The plugin catalog lists released plugins with their install guides:

• Bellows: faster start-up and simulation, without changing game files or game behaviour; also on the Steam Workshop.
• Tongs: lets scripts and agents control a running game through a local pipe, with an MCP server; also on the Steam Workshop (unlisted).

Etch, a preview for EU4 interface mods in Visual Studio Code, is built on Anvil too: its game host runs a private copy of the game with pinned builds of Anvil, anvil-game, Bellows and Etch's own plugin. It is not a catalog plugin. To write a plugin, start from the plugin template and the author docs.

Building

Requirements: Visual Studio 2022 (or Build Tools) with the C++ workload, CMake ≥ 3.25, Git (dependencies are fetched at configure time: toml++ 3.4.0, SafetyHook 0.7.0 with Zydis 4.1.0).

cmake -S . -B build -G "Visual Studio 17 2022" -A x64
cmake --build build --config Release
ctest --test-dir build -C Release --output-on-failure
cmake --install build --config Release --component anvil --prefix dist   # version.dll + anvil/ layout

The build also produces anvil.exe, the command-line tool for plugin authors. It shares the anvil_core library (manifests, symbols.toml and its verification, settings.toml, the game build identity) with version.dll:

anvil gen symbols.toml build\generated            # symbols.gen.h and symbols.gen.hpp
anvil gen settings.toml build\generated           # settings.gen.h and settings.gen.hpp
anvil gen --lang rust symbols.toml out            # symbols.gen.rs (Rust plugins, anvil-sys)
anvil check my-plugin --exe "C:\...\eu4.exe"     # verify against the game, write symbols.lock
anvil check my-plugin --format github             # in CI, without the game: schemas and symbols.lock

The Rust side (sdk/rust/anvil-sys, examples/hello-rust, see §9) is a Cargo workspace at the root; it needs Rust 1.82 or newer and the anvil.exe built above, which the hello's build.rs runs. CI uses Rust 1.99.1, and sdk/rust/regen-bindings.ps1 (bindgen 0.73.2 and libclang) regenerates the committed bindings after a change to the header:

$env:ANVIL = "$PWD\build\Release\anvil.exe"
cargo build --workspace
cargo test --workspace

See docs/design.md §16 for the checks, the instruction-boundary rule and the symbols.lock format.

Contributions, the commit convention and the release process: see CONTRIBUTING.md.

License

MIT — see LICENSE. Anvil is an unofficial community project, not affiliated with or endorsed by Paradox Interactive.