HTTPolice is a Python package that can be installed with pip (on Python 2.7 or 3.4+):

$ pip 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 /analytics.js
------------ response: 200 OK
C 1035 Deprecated media type text/javascript
D 1168 Age header implies response from cache
C 1258 HTTP/2 should use ALTSVC frame instead of Alt-Svc header
------------ request: GET /r/collect?v=1&_v=j49&a=2057119860&t=pageview&_s=1...
------------ response: 200 OK
E 1108 Wrong day of week in Expires
C 1162 Pragma: no-cache is for requests
C 1258 HTTP/2 should use ALTSVC frame instead of Alt-Svc header
------------ request: GET /repos/h2o/h2o?callback=callback
------------ response: 200 OK
C 1277 Obsolete 'X-' prefix in X-RateLimit-Limit
C 1277 Obsolete 'X-' prefix in X-RateLimit-Remaining
C 1277 Obsolete 'X-' prefix in X-RateLimit-Reset
C 1277 Obsolete 'X-' prefix in X-Served-By

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 -ksiX POST https://eve-demo.herokuapp.com/people \
>   -H 'Content-Type: application/json' \
>   -d '{"firstname":"John", "lastname":"Smith"}'
Connection: keep-alive
Content-Type: application/json
Content-Length: 279
Server: Eve/0.6.1 Werkzeug/0.10.4 Python/2.7.4
Date: Mon, 25 Apr 2016 09:21:32 GMT
Via: 1.1 vegur

{"_links": {"self": {"href": "people/571de19c4fd7bd0003356826", "title": "person"}}, "_etag": "3b1f9c356f87a615645e2e51f8d3e05e0e462c03", "_id": "571de19c4fd7bd0003356826", "_created": "Mon, 25 Apr 2016 09:21:32 GMT", "_updated": "Mon, 25 Apr 2016 09:21:32 GMT", "_status": "OK"}

How do you get this into HTTPolice?

One way is to use mitmproxy, an advanced tool for intercepting HTTP traffic. Install it in a Python 3.5+ environment with HTTPolice integration:

$ pip3 install mitmproxy-HTTPolice

(see also the instructions for installing mitmproxy from source).

We’re going to use mitmproxy’s command-line tool—mitmdump. The following command will start mitmdump as a reverse proxy in front of your API on port 8080, with HTTPolice integration:

$ mitmdump --reverse https://eve-demo.herokuapp.com \
>   -s "`python3 -m mitmproxy_httpolice` -o html -w report.html --tail 5"

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

$ curl -ksiX POST https://localhost:8080/people \
>   -H 'Content-Type: application/json' \
>   -d '{"firstname":"Mark", "lastname":"Williams"}'

In the output of mitmdump, you will see that it has intercepted the exchange. Now you can open report.html and see what HTTPolice thinks of it. With the --tail 5 option, report.html will always contain the last 5 exchanges seen by mitmproxy (the latest one is at the bottom).


If you prefer Fiddler over mitmproxy, you can use Fiddler’s HAR 1.2 export to get the data into HTTPolice.

Django integration

Suppose you’re building a Web application with Django (1.8+). 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.

$ pip 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
C 1070 No User-Agent header
------------ 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.