diff --git a/core/cli.zsh b/core/cli.zsh
new file mode 100644
index 000000000..8c0fabb82
--- /dev/null
+++ b/core/cli.zsh
@@ -0,0 +1,195 @@
+#!/usr/bin/env zsh
+
+function omz {
+    [[ $# -gt 0 ]] || {
+        _omz::help
+        return 1
+    }
+
+    local command="$1"
+    shift
+
+    # Subcommand functions start with _ so that they don't
+    # appear as completion entries when looking for `omz`
+    (( $+functions[_omz::$command] )) || {
+        _omz::help
+        return 1
+    }
+
+    _omz::$command "$@"
+}
+
+function _omz {
+    local -a cmds subcmds
+    cmds=(
+        'help:Usage information'
+        'pr:Commands for Oh My Zsh Pull Requests'
+    )
+
+    if (( CURRENT == 2 )); then
+        _describe 'command' cmds
+    elif (( CURRENT == 3 )); then
+        case "$words[2]" in
+            pr) subcmds=( 'test:Test a Pull Request' 'clean:Delete all Pull Request branches' )
+                _describe 'command' subcmds ;;
+        esac
+    fi
+
+    return 0
+}
+
+compdef _omz omz
+
+
+function _omz::help {
+    cat <<EOF
+Usage: omz <command> [options]
+
+Available commands:
+
+    help                Print this help message
+    pr <command>        Commands for Oh My Zsh Pull Requests
+
+EOF
+}
+
+function _omz::log {
+    # if promptsubst is set, a message with `` or $()
+    # will be run even if quoted due to `print -P`
+    setopt localoptions nopromptsubst
+
+    # $1 = info|warn|error|debug
+    # $@ = text
+
+    local logtype=$1
+    local logname=${${functrace[1]#_}%:*}
+    shift
+
+    # Don't print anything if debug is not active
+    if [[ $logtype = debug && -z $_OMZ_DEBUG ]]; then
+        return
+    fi
+
+    # Choose coloring based on log type
+    case "$logtype" in
+        prompt) print -Pn "%S%F{blue}$logname%f%s: $@" ;;
+        debug) print -P "%F{white}$logname%f: $@" ;;
+        info) print -P "%F{green}$logname%f: $@" ;;
+        warn) print -P "%S%F{yellow}$logname%f%s: $@" ;;
+        error) print -P "%S%F{red}$logname%f%s: $@" ;;
+    esac >&2
+}
+
+function _omz::pr {
+    (( $# > 0 && $+functions[_omz::pr::$1] )) || {
+        cat <<EOF
+Usage: omz pr <command> [options]
+
+Available commands:
+
+    clean                       Delete all PR branches (ohmyzsh/pull-*)
+    test <PR_number_or_URL>     Fetch PR #NUMBER and rebase against master
+
+EOF
+        return 1
+    }
+
+    local command="$1"
+    shift
+
+    _omz::pr::$command "$@"
+}
+
+function _omz::pr::clean {
+    (
+        set -e
+        cd -q "$ZSH"
+
+        _omz::log info "removing all Oh My Zsh Pull Request branches..."
+        command git branch --list 'ohmyzsh/pull-*' | while read branch; do
+            command git branch -D "$branch"
+        done
+    )
+}
+
+function _omz::pr::test {
+    # Allow $1 to be a URL to the pull request
+    if [[ "$1" = https://* ]]; then
+        1="${1:t}"
+    fi
+
+    # Check the input
+    if ! [[ -n "$1" && "$1" =~ ^[[:digit:]]+$ ]]; then
+        echo >&2 "Usage: omz pr test <PR_NUMBER_or_URL>"
+        return 1
+    fi
+
+    # Save current git HEAD
+    local branch
+    branch=$(cd -q "$ZSH"; git symbolic-ref --short HEAD) || {
+        _omz::log error "error when getting the current git branch. Aborting..."
+        return 1
+    }
+
+
+    # Fetch PR onto ohmyzsh/pull-<PR_NUMBER> branch and rebase against master
+    # If any of these operations fail, undo the changes made
+    (
+        set -e
+        cd -q "$ZSH"
+
+        # Get the ohmyzsh git remote
+        command git remote -v | while read remote url _; do
+            case "$url" in
+            https://github.com/ohmyzsh/ohmyzsh(|.git)) found=1; break ;;
+            git@github.com:ohmyzsh/ohmyzsh(|.git)) found=1; break ;;
+            esac
+        done
+
+        (( $found )) || {
+            _omz::log error "could not found the ohmyzsh git remote. Aborting..."
+            return 1
+        }
+
+        # Fetch pull request head
+        _omz::log info "fetching PR #$1 to ohmyzsh/pull-$1..."
+        command git fetch -f "$remote" refs/pull/$1/head:ohmyzsh/pull-$1 || {
+            _omz::log error "error when trying to fetch PR #$1."
+            return 1
+        }
+
+        # Rebase pull request branch against the current master
+        _omz::log info "rebasing PR #$1..."
+        command git rebase master ohmyzsh/pull-$1 || {
+            command git rebase --abort &>/dev/null
+            _omz::log warn "could not rebase PR #$1 on top of master."
+            _omz::log warn "you might not see the latest stable changes."
+            _omz::log info "run \`zsh\` to test the changes."
+            return 1
+        }
+
+        _omz::log info "fetch of PR #${1} successful."
+    )
+
+    # If there was an error, abort running zsh to test the PR
+    [[ $? -eq 0 ]] || return 1
+
+    # Run zsh to test the changes
+    _omz::log info "running \`zsh\` to test the changes. Run \`exit\` to go back."
+    command zsh -l
+
+    # After testing, go back to the previous HEAD if the user wants
+    _omz::log prompt "do you want to go back to the previous branch? [Y/n] "
+    read -r -k 1
+    [[ "$REPLY" = [nN] ]] && return
+
+    (
+        set -e
+        cd -q "$ZSH"
+
+        command git checkout "$branch" -- || {
+            _omz::log error "could not go back to the previous branch ('$branch')."
+            return 1
+        }
+    )
+}
diff --git a/oh-my-zsh.sh b/oh-my-zsh.sh
index 30259372c..bfb538423 100644
--- a/oh-my-zsh.sh
+++ b/oh-my-zsh.sh
@@ -73,6 +73,11 @@ else
 fi
 
 
+# Load core files
+for core_file ($ZSH/core/*.zsh); do
+  source "$core_file"
+done
+
 # Load all of the config files in ~/oh-my-zsh that end in .zsh
 # TIP: Add files you don't want in git to .gitignore
 for config_file ($ZSH/lib/*.zsh); do