Response Plugins

Last updated: 3 minutes read.

Since Tyk 3.0 we have incorporated response hooks, this type of hook allows you to modify the response object returned by the upstream. The flow is follows:

  • Tyk receives the request.
  • Tyk runs the full middleware chain, including any other plugins hooks like Pre, Post, Custom Authentication, etc.
  • Tyk sends the request to your upstream API.
  • The request is received by Tyk and the response hook is triggered.
  • Your plugin modifies the response and sends it back to Tyk.
  • Tyk takes the modified response and is received by the client.

This snippet illustrates the hook function signature:

def ResponseHook(request, response, session, metadata, spec):
    tyk.log("ResponseHook is called", "info")
    # In this hook we have access to the response object, to inspect it, uncomment the following line:
    # print(response)
    tyk.log("ResponseHook: upstream returned {0}".format(response.status_code), "info")
    # Attach a new response header:
    response.headers["injectedkey"] = "injectedvalue"
    return response

If working with a Tyk Classic API, you would add this configuration to the API definition:

    "custom_middleware": {
        "response": [
                "name": "ResponseHook",
                "path": "middleware/"
        "driver": "python"
  • driver: set this to the appropriate value for the plugin type (e.g. python, goplugin)
  • response: this is the hook name. You use middleware with the response hook type because you want this custom middleware to process the request on its return leg of a round trip.
  • is your function name from the plugin file.
  • response.path: is the full or relative (to the Tyk binary) path to the plugin source file. Ensure Tyk has read access to this file.

Starting from versions 5.0.4 and 5.1.1+ for our Go, Python and Ruby users we have introduced the multivalue_headers field to facilitate more flexible and efficient management of headers, particularly for scenarios involving a single header key associated with multiple values. The multivalue_headers field, similar to its predecessor, the headers field, is a key-value store. However, it can accommodate an array or list of string values for each key, instead of a single string value. This feature empowers you to represent multiple values for a single header key. Here’s an example of how you might use multivalue_headers, using the Set-Cookie header which often has multiple values:

multivalue_headers = {
    "Set-Cookie": ["sessionToken=abc123; HttpOnly; Secure", "language=en-US; Secure"],

In this example, Set-Cookie header has two associated values: "sessionToken=abc123; HttpOnly; Secure" and "language=en-US; Secure". To help you understand this further, let’s see how multivalue_headers can be used in a Tyk response plugin written in Python:

from tyk.decorators import *
from gateway import TykGateway as tyk

def Del_ResponseHeader_Middleware(request, response, session, metadata, spec):
    # inject a new header with 2 values
    new_header = response.multivalue_headers.add()
    new_header.key = "Set-Cookie"
    new_header.values.extend("sessionToken=abc123; HttpOnly; Secure")
    new_header.values.extend("language=en-US; Secure")
    tyk.log(f"Headers content :\n {response.headers}\n----------", "info")
    tyk.log(f"Multivalue Headers updated :\n {response.multivalue_headers}\n----------", "info")
    return response

In this script, we add 2 values for the Set-Cookie header and then log both: the traditional headers and the new multivalue_headers. This is a great way to monitor your transition to multivalue_headers and ensure that everything is functioning as expected.

Please note, while the headers field will continue to be available and maintained for backward compatibility, we highly encourage the adoption of multivalue_headers for the added flexibility in handling multiple header values.

Go response plugins

Go response plugins have been available since Tyk v3.2.

Supported Response Plugin Languages

See Supported Plugins for details on which languages the response plugin is supported in.