diff --git a/cabal.project b/cabal.project
new file mode 100644
index 0000000..fdadb42
--- /dev/null
+++ b/cabal.project
@@ -0,0 +1,5 @@
+packages:
+  *.cabal
+
+package *
+  ghc-options: -fwrite-ide-info
diff --git a/default.nix b/default.nix
index 989da98..e9283d7 100644
--- a/default.nix
+++ b/default.nix
@@ -65,25 +65,12 @@ let
   ## SHELL ##
   ###########
 
-  dev-test-build = pkgs.writeShellScriptBin "dev-test-build" ''
-    #!/usr/bin/env bash
-
-    ## Fail on any error:
-    set -e
-
-    ## Show commands executed:
-    set -x
-
-    hpack
-    fourmolu --mode check app/ src/ test/
-    prettier --check .
-    find . -iname "*.nix" -not -path "*/nix/sources.nix" -print0 | xargs --null nixpkgs-fmt --check &&
-    hlint app/ src/ test/
-    cabal build -O0
-    cabal run -O0 opsops -- --version
-    cabal v1-test
-    cabal haddock -O0
-  '';
+  ## Prepare dev-test-build script:
+  dev-test-build = pkgs.writeShellApplication {
+    name = "dev-test-build";
+    text = builtins.readFile ./nix/dev-test-build.sh;
+    runtimeInputs = [ pkgs.bash pkgs.bc pkgs.moreutils ];
+  };
 
   ## Prepare Nix shell:
   thisShell = thisHaskell.shellFor {
@@ -104,6 +91,7 @@ let
       thisHaskell.haskell-language-server
       thisHaskell.hlint
       thisHaskell.hpack
+      thisHaskell.weeder
 
       ## Other build inputs for various development requirements:
       pkgs.docker-client
diff --git a/nix/dev-test-build.sh b/nix/dev-test-build.sh
new file mode 100644
index 0000000..421a275
--- /dev/null
+++ b/nix/dev-test-build.sh
@@ -0,0 +1,174 @@
+#!/usr/bin/env bash
+
+## Purpose: This script is used to run all the necessary checks and
+## tests for the project.
+
+## Fail on any error:
+set -e
+
+## Declare default styles:
+_sty_bold=""
+_sty_underline=""
+_sty_standout=""
+_sty_normal=""
+_sty_black=""
+_sty_red=""
+_sty_green=""
+_sty_yellow=""
+_sty_blue=""
+_sty_magenta=""
+_sty_cyan=""
+_sty_white=""
+
+## Set styles if we are on terminal:
+if test -t 1; then
+    ## Check if the terminal supports colors:
+    ncolors=$(tput colors)
+
+    ## Defines styles:
+    if test -n "$ncolors" && test "${ncolors}" -ge 8; then
+        _sty_bold="$(tput bold)"
+        _sty_underline="$(tput smul)"
+        _sty_standout="$(tput smso)"
+        _sty_normal="$(tput sgr0)"
+        _sty_black="$(tput setaf 0)"
+        _sty_red="$(tput setaf 1)"
+        _sty_green="$(tput setaf 2)"
+        _sty_yellow="$(tput setaf 3)"
+        _sty_blue="$(tput setaf 4)"
+        _sty_magenta="$(tput setaf 5)"
+        _sty_cyan="$(tput setaf 6)"
+        _sty_white="$(tput setaf 7)"
+    fi
+fi
+
+_clean=""
+
+while getopts ":c" opt; do
+    case ${opt} in
+        c)
+            _clean="true"
+            ;;
+        ?)
+            echo "Invalid option: -${OPTARG}."
+            exit 1
+            ;;
+    esac
+done
+
+_get_now() {
+    t=${EPOCHREALTIME} # remove the decimal separator (s → µs)
+    t=${t%???}         # remove the last three digits (µs → ms)
+    echo "${t}"
+}
+
+_get_diff() {
+    printf "scale=3; %s - %s\n" "${2}" "${1}" | bc
+}
+
+_print_header() {
+    printf "${_sty_bold}${_sty_blue}🔵 Running %s${_sty_normal}" "${1}"
+}
+
+_print_success() {
+    _start="${1}"
+    _until="${2}"
+    _elapsed=$(_get_diff "${_start}" "${_until}")
+    printf "${_sty_bold}${_sty_green} ✅ %ss${_sty_normal}\n" "${_elapsed}"
+}
+
+_clean() {
+    _print_header "clean"
+    _start=$(_get_now)
+    chronic -- cabal clean && chronic -- cabal v1-clean
+    _print_success "${_start}" "$(_get_now)"
+}
+
+_hpack() {
+    _print_header "hpack (v$(hpack --numeric-version))"
+    _start=$(_get_now)
+    chronic -- hpack
+    _print_success "${_start}" "$(_get_now)"
+}
+
+_fourmolu() {
+    _print_header "fourmolu (v$(fourmolu --version | head -n1 | cut -d' ' -f2))"
+    _start=$(_get_now)
+    chronic -- fourmolu --quiet --mode check app/ src/ test/
+    _print_success "${_start}" "$(_get_now)"
+}
+
+_prettier() {
+    _print_header "prettier (v$(prettier --version))"
+    _start=$(_get_now)
+    chronic -- prettier --check .
+    _print_success "${_start}" "$(_get_now)"
+}
+
+_nixpkgs_fmt() {
+    _print_header "nixpkgs-fmt (v$(nixpkgs-fmt --version 2>&1 | cut -d' ' -f2))"
+    _start=$(_get_now)
+    chronic -- find . -iname "*.nix" -not -path "*/nix/sources.nix" -and -not -path "*/website/node_modules/*.nix" -exec nixpkgs-fmt --check {} \;
+    _print_success "${_start}" "$(_get_now)"
+}
+
+_hlint() {
+    _print_header "hlint (v$(hlint --numeric-version))"
+    _start=$(_get_now)
+    chronic -- hlint app/ src/ test/
+    _print_success "${_start}" "$(_get_now)"
+}
+
+_cabal_build() {
+    _print_header "cabal build (v$(cabal --numeric-version))"
+    _start=$(_get_now)
+    chronic -- cabal build -O0
+    _print_success "${_start}" "$(_get_now)"
+}
+
+_cabal_run() {
+    _print_header "cabal run (v$(cabal --numeric-version))"
+    _start=$(_get_now)
+    chronic -- cabal run -O0 opsops -- --version
+    _print_success "${_start}" "$(_get_now)"
+}
+
+_cabal_test() {
+    _print_header "cabal test (v$(cabal --numeric-version))"
+    _start=$(_get_now)
+    chronic -- cabal v1-test
+    _print_success "${_start}" "$(_get_now)"
+}
+
+_weeder() {
+    _print_header "weeder (v$(weeder --version | head -n1 | cut -d' ' -f3))"
+    _start=$(_get_now)
+    chronic -- weeder
+    _print_success "${_start}" "$(_get_now)"
+}
+
+_cabal_haddock() {
+    _print_header "cabal haddock (v$(cabal --numeric-version))"
+    _start=$(_get_now)
+    chronic -- cabal haddock -O0 \
+        --haddock-quickjump \
+        --haddock-hyperlink-source \
+        --haddock-html-location="https://hackage.haskell.org/package/\$pkg-\$version/docs"
+    _print_success "${_start}" "$(_get_now)"
+}
+
+_scr_start=$(_get_now)
+if [ -n "${_clean}" ]; then
+    _clean
+fi
+_hpack
+_fourmolu
+_prettier
+_nixpkgs_fmt
+_hlint
+_cabal_build
+_cabal_run
+_cabal_test
+_weeder
+_cabal_haddock
+printf "Finished all in %ss\n" "$(_get_diff "${_scr_start}" "$(_get_now)")"
diff --git a/weeder.toml b/weeder.toml
new file mode 100644
index 0000000..9256657
--- /dev/null
+++ b/weeder.toml
@@ -0,0 +1,11 @@
+roots = [
+  ## Definitions we always need:
+  "^Main.main$",
+  "^Opsops.Cli.*$",
+  "^Paths_opsops.*",
+
+  ## Temporary suspensions:
+  "^Zamazingo.*",
+  "^Opsops.Spec._testJsonRoundtrip$"
+]
+type-class-roots = true