HTTPolice is a Python package that can be installed with pip (on Python 3.4+):

$ pip3 install HTTPolice

If you’re not familiar with pip, check the manual’s Installation section.

Using HAR files

Let’s start with something easy.

If you’re running Google Chrome, Firefox, or Microsoft Edge, you can use their developer tools to export HTTP requests and responses as a HAR file, which can then be analyzed by HTTPolice.

For example, in Firefox, press F12 to open the toolbox, and switch to its Network pane. Then, open a simple Web site—I’m going to use h2o.examp1e.net here. All HTTP exchanges made by the browser appear in the Network pane. Right-click inside that pane and select “Save All As HAR”.

Then feed this HAR file to HTTPolice:

$ httpolice -i har /path/to/file.har
------------ request: GET /
------------ response: 200 OK
E 1000 Syntax error in Server header
E 1013 Multiple Date headers are forbidden
------------ request: GET /search/oktavia-english-search.js
------------ response: 200 OK
E 1000 Syntax error in Server header
E 1013 Multiple Date headers are forbidden
C 1277 Obsolete 'X-' prefix in headers
------------ request: GET /assets/8mbps100msec-nginx195-h2o150.png
C 1276 Accept: */* is as good as image/webp
[...and so on...]

Better reports

By default, HTTPolice prints a simple text report which may be hard to understand. Use the -o html option to make a detailed HTML report instead. You will also need to redirect it to a file:

$ httpolice -i har -o html /path/to/file.har >report.html

Open report.html in your Web browser and enjoy.

Using mitmproxy

What if you have an HTTP API that is accessed by special clients? Let’s say curl is special enough:

$ curl -ksi \
>   -X PATCH https://eve-demo.herokuapp.com/people/5ab12b10662d240004d08b31 \
>   -H 'Content-Type: application/json' \
>   -H 'If-Match: 9f5cdb43a57b04abe342f6a425260f5e6adae359' \
>   -d '{"firstname": "John"}'
HTTP/1.1 200 OK
Connection: keep-alive
Content-Type: application/json
Content-Length: 279
Etag: "9a056970404b9dd20c94c274fbdd6db2239800ac"
Server: Eve/0.7.6 Werkzeug/0.10.4 Python/2.7.4
Date: Sat, 31 Mar 2018 13:23:08 GMT
Via: 1.1 vegur

{"_updated": "Sat, 31 Mar 2018 13:23:08 GMT", "_id": "5ab12b10662d240004d08b31", "_links": {"self": {"title": "person", "href": "people/5ab12b10662d240004d08b31"}}, "_status": "OK", "_etag": "9a056970404b9dd20c94c274fbdd6db2239800ac", "_created": "Tue, 20 Mar 2018 15:38:56 GMT"}

How do you get this into HTTPolice?

One way is to use mitmproxy, an advanced tool for inspecting HTTP traffic. Install it in a Python 3.6+ environment with HTTPolice integration:

$ pip3 install mitmproxy-HTTPolice

See also the instructions for installing mitmproxy via pip3.

Doesn’t work on Windows

Try the Windows Subsystem for Linux, or use Fiddler instead (Fiddler’s HAR 1.2 export can get your data into HTTPolice).

The following command will start mitmproxy as a reverse proxy in front of your API on port 8080, with HTTPolice integration:

$ mitmproxy --mode reverse:https://eve-demo.herokuapp.com \
>   -s "`python3 -m mitmproxy_httpolice`"

Now tell your client to talk to port 8080 instead of directly to the API:

$ curl -ksi \
>   -X PATCH https://localhost:8080/people/5ab12b10662d240004d08b31 \
>   -H 'Content-Type: application/json' \
>   -H 'If-Match: 9a056970404b9dd20c94c274fbdd6db2239800ac' \
>   -d '{"firstname": "Sam"}'

In mitmproxy, you will see that it has intercepted the exchange. Open its details (Enter → Tab → Tab) to see the HTTPolice report on it:


Django integration

Suppose you’re building a Web application with Django (1.11+). You probably have a test suite that makes requests to your app and checks responses. You can easily instrument this test suite with HTTPolice and get instant feedback when you break the protocol.

$ pip3 install Django-HTTPolice

Add the HTTPolice middleware to the top of your middleware list:

    # ...

Add a couple settings:


Now let’s run the tests and see what’s broken:

$ python manage.py test
ERROR: test_query_plain (example_app.test.ExampleTestCase)
Traceback (most recent call last):
  File "[...]/django_httpolice/middleware.py", line 92, in process_response
    raise ProtocolError(exchange)
django_httpolice.common.ProtocolError: HTTPolice found problems in this response:
------------ request: GET /api/v1/words/?query=er
------------ response: 200 OK
E 1038 Bad JSON body

Ran 4 tests in 0.380s

FAILED (errors=1)

In this example, the app sent a wrong Content-Type header and HTTPolice caught it.

More options

There are other ways to get your data into HTTPolice. Check the full manual.