diff --git a/common/lib/codejail/README b/common/lib/codejail/README
index 75862d69e3..889534a0c3 100644
--- a/common/lib/codejail/README
+++ b/common/lib/codejail/README
@@ -1,40 +1,75 @@
-Choose a place for the virtualenv, call it <SANDENV>.  It will be automatically
-detected and used if you put it right alongside your existing virtualenv, but
-with -sandbox appended.  So if your existing virtualenv is in ~/mitx_all/python,
-make <SANDENV> be ~/mitx_all/python-sandbox (but you'll need to spell out your
-home directory instead of ~).
+CodeJail
+========
+
+CodeJail manages execution of untrusted code in secure sandboxes. It is
+designed primarily for Python execution, but can be used for other languages as
+well.
+
+Security is enforced with AppArmor.  If your operating system doesn't support
+AppArmor, then CodeJail won't protect the execution.
+
+CodeJail is designed to be configurable, and will auto-configure itself for
+Python execution if you install it properly.  The configuration is designed to
+be flexible: it can run in safe more or unsafe mode.  This helps support large
+development groups where only some of the developers are involved enough with
+secure execution to configure AppArmor on their development machines.
+
+If CodeJail is not configured for safe execution, it will execution Python
+using the same API, but will not guard against malicious code.  This allows the
+same code to be used on safe-configured or non-safe-configured developer's
+machines.
+
+
+Installation
+------------
+
+These instructions detail how to configure your operating system so that
+CodeJail can execute Python code safely.  You can run CodeJail without these
+steps, and you will have an unsafe CodeJail.  This is fine for developers'
+machines who are unconcerned with security, and simplifies the integration of
+CodeJail into your project.
+
+To secure Python execution, you'll be creating a new virtualenv.  This means
+you'll have two: the main virtualenv for your project, and the new one for
+sandboxed Python code.
+
+Choose a place for the new virtualenv, call it <SANDENV>.  It will be
+automatically detected and used if you put it right alongside your existing
+virtualenv, but with -sandbox appended.  So if your existing virtualenv is in
+~/ve/myproj, make <SANDENV> be ~/ve/myproj-sandbox (but you'll need to spell
+out your home directory instead of ~).
 
 Other details here that depend on your configuration:
 
     - Your mitx working tree is <MITX>, for example, ~/mitx_all/mitx
 
-    - The user running the LMS is <USER>, for example, you on a dev machine,
+    - The user running the LMS is <USER>, for example, you on your dev machine,
       or www-data on a server.
 
-Create a virtualenv:
+1. Create the new virtualenv::
 
     $ sudo virtualenv <SANDENV>
 
-Install the sandbox requirements
+2. Install the sandbox requirements::
 
     $ source <SANDENV>/bin/activate
     $ sudo pip install -r sandbox-requirements.txt
 
-Add a sandbox user:
+3. Add a sandbox user::
 
     $ sudo addgroup sandbox
     $ sudo adduser --disabled-login sandbox --ingroup sandbox
 
-Let the web server run the sandboxed Python as sandbox.  Create the file
-/etc/sudoers.d/01-sandbox:
+4. Let the web server run the sandboxed Python as sandbox.  Create the file
+/etc/sudoers.d/01-sandbox::
 
     $ visudo -f /etc/sudoers.d/01-sandbox
 
     <USER> ALL=(sandbox) NOPASSWD:<SANDENV>/bin/python
     <USER> ALL=(ALL) NOPASSWD:/bin/kill
 
-Edit an AppArmor profile.  The file must be named for the python executable,
-but with slashes changed to dots:
+5. Edit an AppArmor profile.  The file must be named for the python executable,
+but with slashes changed to dots::
 
     #include <tunables/global>
 
@@ -49,8 +84,18 @@ but with slashes changed to dots:
         /tmp/** rix,
     }
 
-Parse the profiles
+6. Parse the profiles::
 
     $ sudo apparmor_parser <APPARMOR_FILE>
 
-Reactivate your real virtualenv again
+7. Reactivate your project's main virtualenv again.
+
+
+Tests
+=====
+
+The tests run under nose in the standard fashion.
+
+If CodeJail is running unsafely, many of the tests will be automatically
+skipped, or will fail, depending on whether CodeJail thinks it should be in
+safe mode or not.