diff --git a/README.md b/README.md
index c24e00f..55393fe 100644
--- a/README.md
+++ b/README.md
@@ -27,18 +27,18 @@ e.g. After cloning do:
 
 Extensions | Tools
 ---------- | -----
-.py | python_syntax • python_unittests • pydoc • [mypy](http://www.mypy-lang.org/) • [python_coverage](http://nedbatchelder.com/code/coverage/) • python_profile • [pycodestyle](https://pypi.python.org/pypi/pycodestyle) • [pyflakes](https://launchpad.net/pyflakes) • [pylint](http://www.pylint.org/) • python_gut • python_modulefinder • [python_mccabe](https://github.com/flintwork/mccabe) • [bandit](https://wiki.openstack.org/wiki/Security/Projects/Bandit)
-.pyc | disassemble_pyc
-.pl .pm .t | perl_syntax • perldoc • perltidy
-.pod .pod6 | perldoc
+.py | [python_syntax](https://en.wikipedia.org/wiki/Python_syntax_and_semantics) • [python_unittests](https://docs.python.org/3/library/unittest.html) • [pydoc](https://docs.python.org/3/library/pydoc.html) • [mypy](http://www.mypy-lang.org/) • [python_coverage](http://nedbatchelder.com/code/coverage/) • [python_profile](https://docs.python.org/3/library/profile.html) • [pycodestyle](https://pypi.python.org/pypi/pycodestyle) • [pyflakes](https://launchpad.net/pyflakes) • [pylint](http://www.pylint.org/) • [python_gut](https://github.com/ahamilton/vigil/blob/master/gut.py) • [python_modulefinder](https://docs.python.org/3/library/modulefinder.html) • [python_mccabe](https://github.com/flintwork/mccabe) • [bandit](https://wiki.openstack.org/wiki/Security/Projects/Bandit)
+.pyc | [disassemble_pyc](https://docs.python.org/3/library/dis.html)
+.pl .pm .t | [perl_syntax](https://en.wikipedia.org/wiki/Perl) • [perldoc](http://perldoc.perl.org/) • [perltidy](http://perltidy.sourceforge.net/)
+.pod .pod6 | [perldoc](http://perldoc.perl.org/)
 .java | [uncrustify](http://uncrustify.sourceforge.net/)
 .c .h | [splint](http://www.splint.org/) • [uncrustify](http://uncrustify.sourceforge.net/)
-.o | objdump_headers • objdump_disassemble • readelf
+.o | [objdump_headers](https://en.wikipedia.org/wiki/Objdump) • [objdump_disassemble](https://en.wikipedia.org/wiki/Objdump) • [readelf](https://en.wikipedia.org/wiki/Objdump)
 .cpp | bcpp • [uncrustify](http://uncrustify.sourceforge.net/)
 .pdf | [pdf2txt](http://www.unixuser.org/~euske/python/pdfminer/)
 .html | [html_syntax](http://www.html-tidy.org/) • [tidy](http://www.html-tidy.org/) • [html2text](http://www.mbayer.de/html2text/)
-.php | php5_syntax
+.php | [php5_syntax](https://en.wikipedia.org/wiki/PHP)
 .zip | [unzip](http://www.info-zip.org/UnZip.html)
-.tar.gz .tgz | tar_gz
-.tar.bz2 | tar_bz2
-.a .so | nm
+.tar.gz .tgz | [tar_gz](http://www.gnu.org/software/tar/manual/tar.html)
+.tar.bz2 | [tar_bz2](http://www.gnu.org/software/tar/manual/tar.html)
+.a .so | [nm](https://linux.die.net/man/1/nm)
diff --git a/tools.py b/tools.py
index 0a6f314..46c5bb3 100644
--- a/tools.py
+++ b/tools.py
@@ -296,6 +296,7 @@ def python_syntax(path):
     python_version = _python_version(path)
     return _run_command([python_version, "-m", "py_compile", path])
 python_syntax.dependencies = {"python", "python3"}
+python_syntax.url = "https://en.wikipedia.org/wiki/Python_syntax_and_semantics"
 
 
 def _has_shebang_line(path):
@@ -318,6 +319,7 @@ def python_unittests(path):
     else:
         return Status.not_applicable, fill3.Text("No tests.")
 python_unittests.dependencies = {"python", "python3"}
+python_unittests.url = "https://docs.python.org/3/library/unittest.html"
 
 
 def pydoc(path):
@@ -332,6 +334,7 @@ def pydoc(path):
         status = Status.not_applicable
     return status, fill3.Text(output)
 pydoc.dependencies = {"python", "python3"}
+pydoc.url = "https://docs.python.org/3/library/pydoc.html"
 
 
 def mypy(path):
@@ -379,6 +382,7 @@ def python_profile(path):
                                  "--sort=cumulative", path], timeout=TIMEOUT)
     return Status.normal, fill3.Text(stdout)
 python_profile.dependencies = {"python", "python3"}
+python_profile.url = "https://docs.python.org/3/library/profile.html"
 
 
 def pycodestyle(path):
@@ -408,12 +412,14 @@ def python_gut(path):
     source_widget = _syntax_highlight_using_path(_fix_input(output), path)
     return Status.normal, source_widget
 python_gut.dependencies = set()
+python_gut.url = "https://github.com/ahamilton/vigil/blob/master/gut.py"
 
 
 def python_modulefinder(path):
     return _run_command([_python_version(path), "-m", "modulefinder", path],
                         Status.normal)
 python_modulefinder.dependencies = {"python", "python3"}
+python_modulefinder.url = "https://docs.python.org/3/library/modulefinder.html"
 
 
 def _get_mccabe_line_score(line, python_version):
@@ -454,6 +460,7 @@ def disassemble_pyc(path):
     stringio.seek(0)
     return Status.normal, fill3.Text(stringio.read())
 disassemble_pyc.dependencies = set()
+disassemble_pyc.url = "https://docs.python.org/3/library/dis.html"
 
 
 def bandit(path):
@@ -479,6 +486,7 @@ def perl_syntax(path):
     return _run_command([_perl_version(path), "-c", path])
 # perl_syntax.dependencies = {"perl", "rakudo"}
 perl_syntax.dependencies = {"perl"}
+perl_syntax.url = "https://en.wikipedia.org/wiki/Perl"
 
 
 def perldoc(path):
@@ -486,12 +494,14 @@ def perldoc(path):
     return ((Status.normal, fill3.Text(stdout)) if returncode == 0
             else (Status.not_applicable, fill3.Text(stderr)))
 perldoc.dependencies = {"perl-doc"}
+perldoc.url = "http://perldoc.perl.org/"
 
 
 def perltidy(path):
     stdout, *rest = _do_command(["perltidy", "-st", path])
     return Status.normal, _syntax_highlight_using_path(stdout, path)
 perltidy.dependencies = {"perltidy"}
+perltidy.url = "http://perltidy.sourceforge.net/"
 
 
 # def perl6_syntax(path):
@@ -507,9 +517,13 @@ splint.dependencies = {"splint"}
 splint.url = "splint"
 
 
+_OBJDUMP_URL = "https://en.wikipedia.org/wiki/Objdump"
+
+
 def objdump_headers(path):
     return _run_command(["objdump", "--all-headers", path], Status.normal)
 objdump_headers.dependencies = {"binutils"}
+objdump_headers.url = _OBJDUMP_URL
 
 
 def objdump_disassemble(path):
@@ -517,11 +531,13 @@ def objdump_disassemble(path):
         ["objdump", "--disassemble", "--reloc", "--dynamic-reloc", path],
         Status.normal)
 objdump_disassemble.dependencies = {"binutils"}
+objdump_disassemble.url = _OBJDUMP_URL
 
 
 def readelf(path):
     return _run_command(["readelf", "--all", path], Status.normal)
 readelf.dependencies = {"binutils"}
+readelf.url = _OBJDUMP_URL
 
 
 def unzip(path):
@@ -530,19 +546,25 @@ unzip.dependencies = {"unzip"}
 unzip.url = "unzip"
 
 
+_TAR_URL = "http://www.gnu.org/software/tar/manual/tar.html"
+
+
 def tar_gz(path):
     return _run_command(["tar", "ztvf", path], Status.normal)
 tar_gz.dependencies = {"tar"}
+tar_gz.url = _TAR_URL
 
 
 def tar_bz2(path):
     return _run_command(["tar", "jtvf", path], Status.normal)
 tar_bz2.dependencies = {"tar"}
+tar_bz2.url = _TAR_URL
 
 
 def nm(path):
     return _run_command(["nm", "--demangle", path], Status.normal)
 nm.dependencies = {"binutils"}
+nm.url = "https://linux.die.net/man/1/nm"
 
 
 def pdf2txt(path):
@@ -597,6 +619,7 @@ uncrustify.url = "uncrustify"
 def php5_syntax(path):
     return _run_command(["php", "--syntax-check", path])
 php5_syntax.dependencies = {"php"}
+php5_syntax.url = "https://en.wikipedia.org/wiki/PHP"
 
 
 #############################