Using the Request Body Transform middleware with Tyk Classic APIs

Last updated: 3 minutes read.

The request body transform middleware provides a way to modify the payload of API requests before they are proxied to the upstream.

This middleware is configured in the Tyk Classic API Definition at the endpoint level. You can do this via the Tyk Dashboard API or in the API Designer.

If you want to use dynamic data from context variables, you must enable context variables for the API to be able to access them from the request header transform middleware.

If you’re using the newer Tyk OAS APIs, then check out the Tyk OAS page.

Configuring the middleware in the Tyk Classic API Definition

To enable the middleware you must add a new transform object to the extended_paths section of your API definition.

The transform object has the following configuration:

  • path: the path to match on
  • method: this method to match on
  • template_data: details of the Go template to be applied for the transformation of the request body

The Go template is described in the template_data object by the following fields:

  • input_type: the format of input data the parser should expect (either xml or json)
  • enable_session: set this to true to make session metadata available to the transform template
  • template_mode: instructs the middleware to look for the template either in a file or in a base64 encoded blob; the actual file location (or base64 encoded template) is provided in template_source
  • template_source: if template_mode is set to file, this will be the path to the text file containing the template; if template_mode is set to blob, this will be a base64 encoded representation of your template

For example:

    "extended_paths": {
        "transform": [
                "path": "/anything",
                "method": "POST",
                "template_data": {
                    "template_mode": "file",
                    "template_source": "./templates/transform_test.tmpl",
                    "input_type": "json",
                    "enable_session": true

In this example, the Request Body Transform middleware is directed to use the template located in the file at location ./templates/transform_test.tmpl. The input (pre-transformation) request payload will be json format and session metadata will be available for use in the transformation.


Tyk will load and evaluate the template file when the Gateway starts up. If you modify the template, you will need to restart Tyk in order for the changes to take effect.

Configuring the middleware in the API Designer

You can use the API Designer in the Tyk Dashboard to configure the request body transform middleware for your Tyk Classic API by following these steps.

Step 1: Add an endpoint for the path and select the plugin

From the Endpoint Designer add an endpoint that matches the path for which you want to perform the transformation. Select the Body Transforms plugin.

Endpoint designer

Step 2: Configure the middleware

Ensure that you have selected the REQUEST tab, then select your input type, and then add the template you would like to use to the Template input box.

Setting the body request transform

Step 3: Test the Transform

If sample input data is available, you can use the Input box to add it, and then test it using the Test button. You will see the effect of the template on the sample input displayed in the Output box.

Testing the body transform function

Step 4: Save the API

Use the save or create buttons to save the changes and activate the Request Body Transform middleware.