diff --git a/php/.tool-versions b/php/.tool-versions
new file mode 100644
index 0000000..13bc26d
--- /dev/null
+++ b/php/.tool-versions
@@ -0,0 +1 @@
+php 8
diff --git a/php/README.md b/php/README.md
index b467e11..b083d0d 100644
--- a/php/README.md
+++ b/php/README.md
@@ -1,23 +1,34 @@
 # PHP
 
-Skeleton project for PHP with PHPUnit for testing.
+Skeleton project for PHP.
 
-## Usage (on MacOS or Linux)
-- `./script/setup` to install dependencies using brew
-    - If this doesn't work install PHP CLI and [Composer](https://getcomposer.org/) manually
-- `./script/test` to run the tests
-- `./script/start` to run the code
+## Prerequisites
+
+The toolchain this project needs is declared in [`.tool-versions`](./.tool-versions):
+
+```
+php 8
+```
 
-*Note: You need [brew](https://brew.sh/) installed for the setup script to work. If you haven't installed brew before it will require at least 5gb of space. Downloading these packages will take a long time, so please ensure you do so well in advance of the interview.*
+Install those however you prefer, as long as they end up on your `PATH`. The quickest route is
+[mise](https://mise.jdx.dev/), which reads the file for you:
 
-## Usage (on Windows)
-- `PowerShell.exe -ExecutionPolicy UnRestricted -File .\script\setup.ps1` to download temp install of php and composer dependencies
-    - If this doesn't work install [PHP](https://www.php.net/manual/en/install.windows.php) and [Composer](https://getcomposer.org/) manually
-- `php composer.phar test` to run the tests
-- `php composer.phar start` to run the code
+```sh
+mise install
+```
+
+Note that mise compiles PHP from source, so it needs some system libraries to build against.
+If `mise install` fails, run [`./script/system-packages`](./script/system-packages) to install
+them and try again. You can skip this if you install PHP from a package manager instead
+(`apt install php`, `brew install php`), as that comes pre-built.
+
+## Usage
+- `./script/setup` to fetch dependencies
+- `./script/test` to run the tests
+- `./script/start` to run the app
 
 ## Structure
 - Code located in [`code.php`](./code.php)
-- Tests located in [`tests.php`](./tests.php)
+- Tests located in [`Tests.php`](./Tests.php)
 
-However, you're free to organise your code as you like. 
+However, you're free to organise your code as you like.
diff --git a/php/composer.json b/php/composer.json
index 594c44d..1c8f665 100644
--- a/php/composer.json
+++ b/php/composer.json
@@ -4,6 +4,7 @@
     },
     "scripts": {
         "start": "php code.php",
-        "test": "phpunit Tests.php"
+        "test": "vendor/bin/phpunit Tests.php"
     }
 }
+
diff --git a/php/script/setup b/php/script/setup
index 296efed..069d192 100755
--- a/php/script/setup
+++ b/php/script/setup
@@ -1,7 +1,21 @@
 #!/usr/bin/env bash
 
-set -e
+set -euo pipefail
 
-brew install php
-brew install phpunit
-brew install composer
+cd "$(dirname "${BASH_SOURCE[0]}")/.."
+
+# Bootstrap composer locally if not present
+if [[ ! -f composer.phar ]]; then
+  EXPECTED_SIG="$(curl -fsSL https://composer.github.io/installer.sig)"
+  php -r "copy('https://getcomposer.org/installer', 'composer-setup.php');"
+  ACTUAL_SIG="$(php -r "echo hash_file('sha384', 'composer-setup.php');")"
+  if [[ "$EXPECTED_SIG" != "$ACTUAL_SIG" ]]; then
+    echo "Composer installer signature verification failed" >&2
+    rm -f composer-setup.php
+    exit 1
+  fi
+  php composer-setup.php
+  rm -f composer-setup.php
+fi
+
+php composer.phar install
diff --git a/php/script/setup.ps1 b/php/script/setup.ps1
deleted file mode 100644
index 4a2973e..0000000
--- a/php/script/setup.ps1
+++ /dev/null
@@ -1,27 +0,0 @@
-$phpZipUrl = "https://windows.php.net/downloads/releases/php-8.1.10-nts-Win32-vs16-x64.zip"
-$phpZipFilename = "php-8.1.10-nts-Win32-vs16-x64.zip"
-$localPhp = "./php"
-
-# Download PHP zip
-Import-Module BitsTransfer
-Start-BitsTransfer -Source $phpZipUrl -Destination $phpZipFilename
-
-# Extract PHP zip
-Expand-Archive -Force -LiteralPath ./$phpZipFilename -DestinationPath $localPhp
-
-# Add downloaded php to path
-$phpPath = (Convert-Path $localPhp)
-$env:PATH = $env:PATH + ";" + $phpPath
-
-php --version
-
-# Copy php config to local install
-cp ./php.ini $localPhp
-
-# Download Composer install php script
-php -r "copy('https://getcomposer.org/installer', 'composer-setup.php');"
-php -r "if (hash_file('sha384', 'composer-setup.php') === '55ce33d7678c5a611085589f1f3ddf8b3c52d662cd01d4ba75c0ee0459970c2200a51f492d557530c71c15d8dba01eae') { echo 'Installer verified'; } else { echo 'Installer corrupt'; unlink('composer-setup.php'); } echo PHP_EOL;"
-php composer-setup.php
-php -r "unlink('composer-setup.php');"
-
-php composer.phar install
\ No newline at end of file
diff --git a/php/script/start b/php/script/start
index 50ebaf2..ee7f767 100755
--- a/php/script/start
+++ b/php/script/start
@@ -1,5 +1,7 @@
 #!/usr/bin/env bash
 
-set -e
+set -euo pipefail
 
-composer run-script start
+cd "$(dirname "${BASH_SOURCE[0]}")/.."
+
+php composer.phar run-script start
diff --git a/php/script/system-packages b/php/script/system-packages
new file mode 100755
index 0000000..ded5c34
--- /dev/null
+++ b/php/script/system-packages
@@ -0,0 +1,92 @@
+#!/usr/bin/env bash
+
+# Installs the system libraries PHP is compiled against.
+#
+# You only need this if you are *building* PHP from source, which is what mise does.
+# If you install PHP from a package manager (apt install php, brew install php) the
+# packaging has already taken care of this and you can skip it.
+#
+# This is separate from `script/setup` because it has to run *before* the toolchain is
+# built. By the time `setup` runs, PHP is already compiled and on your PATH.
+
+set -euo pipefail
+
+# Debian/Ubuntu package names, used by the CI runner and most devcontainers.
+APT_PACKAGES=(
+  autoconf
+  bison
+  build-essential
+  libbz2-dev
+  libcurl4-openssl-dev
+  libfreetype6-dev
+  libgd-dev
+  libgmp-dev
+  libicu-dev
+  libjpeg-dev
+  libonig-dev
+  libpng-dev
+  libpq-dev
+  libreadline-dev
+  libsodium-dev
+  libsqlite3-dev
+  libssl-dev
+  libwebp-dev
+  libxml2-dev
+  libxslt1-dev
+  libzip-dev
+  pkg-config
+  re2c
+  zlib1g-dev
+)
+
+# macOS equivalents. Xcode Command Line Tools provide the compiler toolchain itself.
+BREW_PACKAGES=(
+  autoconf
+  bison
+  freetype
+  gd
+  gettext
+  gmp
+  icu4c
+  jpeg
+  libiconv
+  libpng
+  libsodium
+  libxml2
+  libzip
+  oniguruma
+  pkg-config
+  re2c
+  webp
+)
+
+if command -v apt-get >/dev/null 2>&1; then
+  # Containers often run as root, without sudo installed.
+  if [[ "$(id -u)" -eq 0 ]]; then
+    sudo=()
+  elif command -v sudo >/dev/null 2>&1; then
+    sudo=(sudo)
+  else
+    echo "This script needs root to install packages, but sudo is not available." >&2
+    echo "Re-run it as root, or install these packages yourself:" >&2
+    printf '  %s\n' "${APT_PACKAGES[*]}" >&2
+    exit 1
+  fi
+
+  "${sudo[@]}" apt-get update --quiet
+  "${sudo[@]}" apt-get install --yes --no-install-recommends "${APT_PACKAGES[@]}"
+
+elif command -v brew >/dev/null 2>&1; then
+  brew install "${BREW_PACKAGES[@]}"
+
+else
+  echo "Could not find apt-get or brew, so this script cannot install packages for you." >&2
+  echo "" >&2
+  echo "PHP is compiled from source, and needs the development headers for roughly:" >&2
+  echo "  autoconf bison libcurl libgd libicu libjpeg libpng libsodium libsqlite3" >&2
+  echo "  libssl libxml2 libzip oniguruma pkg-config re2c zlib" >&2
+  echo "" >&2
+  echo "Install the equivalents for your system, or install PHP from your package" >&2
+  echo "manager instead of building it - see .tool-versions for the version needed." >&2
+  exit 1
+fi
diff --git a/php/script/test b/php/script/test
index c69c1ce..6ffdaec 100755
--- a/php/script/test
+++ b/php/script/test
@@ -1,5 +1,7 @@
 #!/usr/bin/env bash
 
-set -e
+set -euo pipefail
 
-composer run-script test
+cd "$(dirname "${BASH_SOURCE[0]}")/.."
+
+php composer.phar run-script test