diff --git a/.config/hakari.toml b/.config/hakari.toml
new file mode 100644
index 0000000..e7d47f1
--- /dev/null
+++ b/.config/hakari.toml
@@ -0,0 +1,27 @@
+# This file contains settings for `cargo hakari`.
+# See https://docs.rs/cargo-hakari/latest/cargo_hakari/config for a full list of options.
+
+hakari-package = "advent-hack"
+
+# Format version for hakari's output. Version 4 requires cargo-hakari 0.9.22 or above.
+dep-format-version = "4"
+
+# Setting workspace.resolver = "2" or higher in the root Cargo.toml is HIGHLY recommended.
+# Hakari works much better with the v2 resolver. (The v2 and v3 resolvers are identical from
+# hakari's perspective, so you're welcome to set either.)
+#
+# For more about the new feature resolver, see:
+# https://blog.rust-lang.org/2021/03/25/Rust-1.51.0.html#cargos-new-feature-resolver
+resolver = "2"
+
+# Add triples corresponding to platforms commonly used by developers here.
+# https://doc.rust-lang.org/rustc/platform-support.html
+platforms = [
+  "x86_64-unknown-linux-gnu",
+  # "x86_64-apple-darwin",
+  # "aarch64-apple-darwin",
+  # "x86_64-pc-windows-msvc",
+]
+
+# Write out exact versions rather than a semver range. (Defaults to false.)
+# exact-versions = true
diff --git a/Cargo.lock b/Cargo.lock
index 57c7f83..115827a 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -6,16 +6,22 @@ version = 4
 name = "advent"
 version = "0.1.0"
 dependencies = [
+ "advent-hack",
  "advent_core",
  "macros",
  "y_2024",
  "y_2025",
 ]
 
+[[package]]
+name = "advent-hack"
+version = "0.1.0"
+
 [[package]]
 name = "advent_core"
 version = "0.1.0"
 dependencies = [
+ "advent-hack",
  "indicatif",
  "regex",
 ]
@@ -106,9 +112,9 @@ dependencies = [
 
 [[package]]
 name = "js-sys"
-version = "0.3.82"
+version = "0.3.83"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "b011eec8cc36da2aab2d5cff675ec18454fad408585853910a202391cf9f8e65"
+checksum = "464a3709c7f55f1f721e5389aa6ea4e3bc6aba669353300af094b29ffbdde1d8"
 dependencies = [
  "once_cell",
  "wasm-bindgen",
@@ -116,14 +122,15 @@ dependencies = [
 
 [[package]]
 name = "libc"
-version = "0.2.177"
+version = "0.2.178"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "2874a2af47a2325c2001a6e6fad9b16a53b802102b528163885171cf92b15976"
+checksum = "37c93d8daa9d8a012fd8ab92f088405fb202ea0b6ab73ee2482ae66af4f42091"
 
 [[package]]
 name = "macros"
 version = "0.1.0"
 dependencies = [
+ "advent-hack",
  "advent_core",
 ]
 
@@ -250,12 +257,15 @@ checksum = "81e544489bf3d8ef66c953931f56617f423cd4b5494be343d9b9d3dda037b9a3"
 [[package]]
 name = "utils"
 version = "0.1.0"
+dependencies = [
+ "advent-hack",
+]
 
 [[package]]
 name = "wasm-bindgen"
-version = "0.2.105"
+version = "0.2.106"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "da95793dfc411fbbd93f5be7715b0578ec61fe87cb1a42b12eb625caa5c5ea60"
+checksum = "0d759f433fa64a2d763d1340820e46e111a7a5ab75f993d1852d70b03dbb80fd"
 dependencies = [
  "cfg-if",
  "once_cell",
@@ -266,9 +276,9 @@ dependencies = [
 
 [[package]]
 name = "wasm-bindgen-macro"
-version = "0.2.105"
+version = "0.2.106"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "04264334509e04a7bf8690f2384ef5265f05143a4bff3889ab7a3269adab59c2"
+checksum = "48cb0d2638f8baedbc542ed444afc0644a29166f1595371af4fecf8ce1e7eeb3"
 dependencies = [
  "quote",
  "wasm-bindgen-macro-support",
@@ -276,9 +286,9 @@ dependencies = [
 
 [[package]]
 name = "wasm-bindgen-macro-support"
-version = "0.2.105"
+version = "0.2.106"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "420bc339d9f322e562942d52e115d57e950d12d88983a14c79b86859ee6c7ebc"
+checksum = "cefb59d5cd5f92d9dcf80e4683949f15ca4b511f4ac0a6e14d4e1ac60c6ecd40"
 dependencies = [
  "bumpalo",
  "proc-macro2",
@@ -289,9 +299,9 @@ dependencies = [
 
 [[package]]
 name = "wasm-bindgen-shared"
-version = "0.2.105"
+version = "0.2.106"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "76f218a38c84bcb33c25ec7059b07847d465ce0e0a76b995e134a45adcb6af76"
+checksum = "cbc538057e648b67f72a982e708d485b2efa771e1ac05fec311f9f63e5800db4"
 dependencies = [
  "unicode-ident",
 ]
@@ -325,6 +335,7 @@ dependencies = [
 name = "y_2024"
 version = "0.1.0"
 dependencies = [
+ "advent-hack",
  "advent_core",
  "macros",
  "rayon",
@@ -336,6 +347,7 @@ dependencies = [
 name = "y_2025"
 version = "0.1.0"
 dependencies = [
+ "advent-hack",
  "advent_core",
  "macros",
  "rayon",
diff --git a/Cargo.toml b/Cargo.toml
index 489214e..f7796c9 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -4,8 +4,8 @@ version = "0.1.0"
 edition = "2021"
 
 [workspace]
-
-members = ["advent_core", "macros", "utils", "years/*"]
+resolver = "3"
+members = ["advent-hack", "advent_core", "macros", "utils", "years/*"]
 
 # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
 
@@ -14,6 +14,7 @@ y_2025 = { path = "years/2025" }
 y_2024 = { path = "years/2024" }
 advent_core = { path = "advent_core" }
 macros = { path = "macros" }
+advent-hack = { version = "0.1", path = "advent-hack" }
 
 [[bin]]
 name = "advent"
diff --git a/advent-hack/.gitattributes b/advent-hack/.gitattributes
new file mode 100644
index 0000000..3e9dba4
--- /dev/null
+++ b/advent-hack/.gitattributes
@@ -0,0 +1,4 @@
+# Avoid putting conflict markers in the generated Cargo.toml file, since their presence breaks
+# Cargo.
+# Also do not check out the file as CRLF on Windows, as that's what hakari needs.
+Cargo.toml merge=binary -crlf
diff --git a/advent-hack/Cargo.toml b/advent-hack/Cargo.toml
new file mode 100644
index 0000000..ead0ab5
--- /dev/null
+++ b/advent-hack/Cargo.toml
@@ -0,0 +1,17 @@
+# This file is generated by `cargo hakari`.
+# To regenerate, run:
+#     cargo hakari generate
+
+[package]
+name = "advent-hack"
+version = "0.1.0"
+edition = "2021"
+description = "workspace-hack package, managed by hakari"
+# You can choose to publish this crate: see https://docs.rs/cargo-hakari/latest/cargo_hakari/publishing.
+publish = false
+
+# The parts of the file between the BEGIN HAKARI SECTION and END HAKARI SECTION comments
+# are managed by hakari.
+
+### BEGIN HAKARI SECTION
+### END HAKARI SECTION
diff --git a/advent-hack/build.rs b/advent-hack/build.rs
new file mode 100644
index 0000000..92518ef
--- /dev/null
+++ b/advent-hack/build.rs
@@ -0,0 +1,2 @@
+// A build script is required for cargo to consider build dependencies.
+fn main() {}
diff --git a/advent-hack/src/lib.rs b/advent-hack/src/lib.rs
new file mode 100644
index 0000000..22489f6
--- /dev/null
+++ b/advent-hack/src/lib.rs
@@ -0,0 +1 @@
+// This is a stub lib.rs.
diff --git a/advent_core/Cargo.toml b/advent_core/Cargo.toml
index c41248b..600b526 100644
--- a/advent_core/Cargo.toml
+++ b/advent_core/Cargo.toml
@@ -8,3 +8,4 @@ edition = "2024"
 [dependencies]
 indicatif = "0.18.3"
 regex = "1.12.2"
+advent-hack = { version = "0.1", path = "../advent-hack" }
diff --git a/flake.nix b/flake.nix
index 345107f..22c4612 100644
--- a/flake.nix
+++ b/flake.nix
@@ -22,6 +22,8 @@
       src = lib.fileset.toSource {
         root = rawSrc;
         fileset = lib.fileset.unions [
+          ./.config/hakari.toml
+          ./advent-hack
           ./advent_core
           ./src
           ./macros
@@ -97,7 +99,13 @@
           default = pkgs: (mkCrane pkgs).buildCrate "advent";
         };
       checks = pkgs: let
-        inherit (mkCrane pkgs) commonArgs craneLib cargoArtifacts;
+        inherit
+          (mkCrane pkgs)
+          src
+          commonArgs
+          craneLib
+          cargoArtifacts
+          ;
       in
         forAllCrates (name: {
           name = "clippy-${name}";
@@ -120,10 +128,30 @@
               cargoNextestPartitionsExtraArgs = "--no-tests=pass -p ${name}";
             }
           );
-        });
+        })
+        // {
+          advent-hakari = craneLib.mkCargoDerivation {
+            inherit src;
+            pname = "advent-hakari";
+            cargoArtifacts = null;
+            doInstallCargoArtifacts = false;
+
+            buildPhaseCargoCommand = ''
+              cargo hakari generate --diff  # workspace-hack Cargo.toml is up-to-date
+              cargo hakari manage-deps --dry-run  # all workspace crates depend on workspace-hack
+              cargo hakari verify
+            '';
+
+            nativeBuildInputs = [
+              pkgs.cargo-hakari
+            ];
+          };
+        };
       devShell = pkgs:
         (mkCrane pkgs).craneLib.devShell {
           checks = self.checks.${pkgs.system};
+
+          packages = with pkgs; [cargo-hakari];
         };
     };
 }
diff --git a/macros/Cargo.toml b/macros/Cargo.toml
index 4883d5a..b2644c7 100644
--- a/macros/Cargo.toml
+++ b/macros/Cargo.toml
@@ -10,3 +10,4 @@ proc-macro = true
 
 [dependencies]
 advent_core = { path = "../advent_core" }
+advent-hack = { version = "0.1", path = "../advent-hack" }
diff --git a/utils/Cargo.toml b/utils/Cargo.toml
index bd645df..be84d13 100644
--- a/utils/Cargo.toml
+++ b/utils/Cargo.toml
@@ -2,3 +2,6 @@
 name = "utils"
 version = "0.1.0"
 edition = "2021"
+
+[dependencies]
+advent-hack = { version = "0.1", path = "../advent-hack" }
diff --git a/years/2024/Cargo.toml b/years/2024/Cargo.toml
index bac3e2e..fb3e405 100644
--- a/years/2024/Cargo.toml
+++ b/years/2024/Cargo.toml
@@ -10,3 +10,4 @@ macros = { path = "../../macros" }
 rayon = "1.11.0"
 regex = "1.12.2"
 utils = { path = "../../utils" }
+advent-hack = { version = "0.1", path = "../../advent-hack" }
diff --git a/years/2025/Cargo.toml b/years/2025/Cargo.toml
index e025283..31d4f59 100644
--- a/years/2025/Cargo.toml
+++ b/years/2025/Cargo.toml
@@ -9,3 +9,4 @@ advent_core = { path = "../../advent_core" }
 macros = { path = "../../macros" }
 rayon = "1.11.0"
 utils = { path = "../../utils" }
+advent-hack = { version = "0.1", path = "../../advent-hack" }