diff --git a/Library/Homebrew/dev-cmd/linkage.rb b/Library/Homebrew/dev-cmd/linkage.rb
new file mode 100644
index 0000000000..e4da827f24
--- /dev/null
+++ b/Library/Homebrew/dev-cmd/linkage.rb
@@ -0,0 +1,32 @@
+#:  * `linkage` [`--test`] [`--reverse`]  <formula>:
+#:    Checks the library links of an installed formula.
+#:
+#:    Only works on installed formulae. An error is raised if it is run on
+#:    uninstalled formulae.
+#:
+#:    If `--test` is passed, only display missing libraries and exit with a
+#:    non-zero exit code if any missing libraries were found.
+#:
+#:    If `--reverse` is passed, print the dylib followed by the binaries
+#:    which link to it for each library the keg references.
+
+require "os/mac/linkage_checker"
+
+module Homebrew
+  module_function
+
+  def linkage
+    ARGV.kegs.each do |keg|
+      ohai "Checking #{keg.name} linkage" if ARGV.kegs.size > 1
+      result = LinkageChecker.new(keg)
+      if ARGV.include?("--test")
+        result.display_test_output
+        Homebrew.failed = true if result.broken_dylibs?
+      elsif ARGV.include?("--reverse")
+        result.display_reverse_output
+      else
+        result.display_normal_output
+      end
+    end
+  end
+end
diff --git a/Library/Homebrew/os/mac/linkage_checker.rb b/Library/Homebrew/os/mac/linkage_checker.rb
new file mode 100644
index 0000000000..c758602049
--- /dev/null
+++ b/Library/Homebrew/os/mac/linkage_checker.rb
@@ -0,0 +1,142 @@
+require "set"
+require "keg"
+require "formula"
+
+class LinkageChecker
+  attr_reader :keg, :formula
+  attr_reader :brewed_dylibs, :system_dylibs, :broken_dylibs, :variable_dylibs
+  attr_reader :undeclared_deps, :reverse_links
+
+  def initialize(keg, formula = nil)
+    @keg = keg
+    @formula = formula || resolve_formula(keg)
+    @brewed_dylibs = Hash.new { |h, k| h[k] = Set.new }
+    @system_dylibs = Set.new
+    @broken_dylibs = Set.new
+    @variable_dylibs = Set.new
+    @undeclared_deps = []
+    @reverse_links = Hash.new { |h, k| h[k] = Set.new }
+    check_dylibs
+  end
+
+  def check_dylibs
+    @keg.find do |file|
+      next if file.symlink? || file.directory?
+      next unless file.dylib? || file.mach_o_executable? || file.mach_o_bundle?
+
+      # weakly loaded dylibs may not actually exist on disk, so skip them
+      # when checking for broken linkage
+      file.dynamically_linked_libraries.each do |dylib|
+        @reverse_links[dylib] << file
+        if dylib.start_with? "@"
+          @variable_dylibs << dylib
+        else
+          begin
+            owner = Keg.for Pathname.new(dylib)
+          rescue NotAKegError
+            @system_dylibs << dylib
+          rescue Errno::ENOENT
+            @broken_dylibs << dylib
+          else
+            tap = Tab.for_keg(owner).tap
+            f = if tap.nil? || tap.core_tap?
+              owner.name
+            else
+              "#{tap}/#{owner.name}"
+            end
+            @brewed_dylibs[f] << dylib
+          end
+        end
+      end
+    end
+
+    @undeclared_deps = check_undeclared_deps if formula
+  end
+
+  def check_undeclared_deps
+    filter_out = proc do |dep|
+      next true if dep.build?
+      next false unless dep.optional? || dep.recommended?
+      formula.build.without?(dep)
+    end
+    declared_deps = formula.deps.reject { |dep| filter_out.call(dep) }.map(&:name)
+    declared_requirement_deps = formula.requirements.reject { |req| filter_out.call(req) }.map(&:default_formula).compact
+    declared_dep_names = (declared_deps + declared_requirement_deps).map { |dep| dep.split("/").last }
+    undeclared_deps = @brewed_dylibs.keys.select do |full_name|
+      name = full_name.split("/").last
+      next false if name == formula.name
+      !declared_dep_names.include?(name)
+    end
+    undeclared_deps.sort do |a, b|
+      if a.include?("/") && !b.include?("/")
+        1
+      elsif !a.include?("/") && b.include?("/")
+        -1
+      else
+        a <=> b
+      end
+    end
+  end
+
+  def display_normal_output
+    display_items "System libraries", @system_dylibs
+    display_items "Homebrew libraries", @brewed_dylibs
+    display_items "Variable-referenced libraries", @variable_dylibs
+    display_items "Missing libraries", @broken_dylibs
+    display_items "Possible undeclared dependencies", @undeclared_deps
+  end
+
+  def display_reverse_output
+    return if @reverse_links.empty?
+    sorted = @reverse_links.sort
+    sorted.each do |dylib, files|
+      puts dylib
+      files.each do |f|
+        unprefixed = f.to_s.strip_prefix "#{@keg}/"
+        puts "  #{unprefixed}"
+      end
+      puts unless dylib == sorted.last[0]
+    end
+  end
+
+  def display_test_output
+    display_items "Missing libraries", @broken_dylibs
+    puts "No broken dylib links" if @broken_dylibs.empty?
+  end
+
+  def broken_dylibs?
+    !@broken_dylibs.empty?
+  end
+
+  def undeclared_deps?
+    !@undeclared_deps.empty?
+  end
+
+  private
+
+  # Display a list of things.
+  # Things may either be an array, or a hash of (label -> array)
+  def display_items(label, things)
+    return if things.empty?
+    puts "#{label}:"
+    if things.is_a? Hash
+      things.sort.each do |list_label, list|
+        list.sort.each do |item|
+          puts "  #{item} (#{list_label})"
+        end
+      end
+    else
+      things.sort.each do |item|
+        puts "  #{item}"
+      end
+    end
+  end
+
+  def resolve_formula(keg)
+    f = Formulary.from_rack(keg.rack)
+    f.build = Tab.for_keg(keg)
+    f
+  rescue FormulaUnavailableError
+    opoo "Formula unavailable: #{keg.name}"
+  end
+end