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Imposter allows you to store data for use later. Benefits:

  • use data from a request in a current or future response
  • store the data sent to a mock for later retrieval/verification
  • set up or seed test data before a mock is used
  • capture data (headers, body etc.) for use by a script
  • return stored data in a response template
  • support for GraphQL queries


You can access Stores via an object in scripts, named stores, and the /system/store REST API.

Using stores in scripts

Here is an example of using the stores object in your scripts.

var exampleStore ='example');

// save the value of the 'foo' query parameter to the store'foo',;

// some other request, later
var previousFoo = exampleStore.load('foo');

Stores also support deletion:


and retrieving all data:

var storeData = exampleStore.loadAll();'foo=' +;'bar=' +;

You can check for the presence of an item by key:

if (exampleStore.hasItemWithKey('example')) {
    // ... there is an item with the key 'example'

Read a store item as JSON:

var json = exampleStore.loadAsJson('foo');

// prints the 'foo' item as JSON

The Stores REST API

You can also retrieve or save data to a store through the /system/store API. This can be useful for tests to verify what was sent to a mock:

$ curl http://localhost:8080/system/store/test/foo

In this example, imagine the item foo in the test store was set to the value ada by a previous request or script (see above).

You can also set data via this API:

$ curl -XPUT --data 'ada' http://localhost:8080/system/store/test/foo

Your scripts can now use the data in the store. This can be useful for test data setup/seeding.

You can retrieve all the items in a store:

$ curl http://localhost:8080/system/store/test
  "foo": "ada",
  "bar": "baz"

Note, you can filter the items returned by their key's prefix, such as:

shell $ curl http://localhost:8080/system/store/test?keyPrefix=fo { "foo": "ada" }

You can delete items in a store:

$ curl -XDELETE http://localhost:8080/system/store/test/foo

This deletes the foo item from the test store.

You can delete an entire store and all of its data:

$ curl -XDELETE http://localhost:8080/system/store/test

This deletes the whole test store and all its data.

You can set multiple items at once via a POST to the store resource:

$ curl -XPOST http://localhost:8080/system/store/test --data '{ "foo": "bar", "baz": "qux" }'

Environment variables

The following environment variables are supported:

Variable name Purpose Default Example(s)
IMPOSTER_STORE_DRIVER Sets the store implementation (see Store implementations section). store-inmem store-dynamodb
IMPOSTER_STORE_KEY_PREFIX Sets an optional prefix for all keys in the store, like a namespace. Empty A prefix of foo would result in the key bar being stored as

Request scoped store

There is a special request-scoped store, named request, which is accessible only to the current request. Its contents do not persist beyond the lifecycle of the request.

The request scoped store is very useful when you need to capture an item for immediate use, such as in a response template, but you don't need to persist it for later use.

Preloading (pre-populating) data into a store

You can preload data into a store when Imposter starts.

To do this, use the system.stores.preloadFile or system.stores.preloadData key in a configuration file.

Preloading from file

Typically, you will provide the data in a JSON file, and use the preloadFile key:

plugin: rest

    # this store is preloaded from file
      preloadFile: initial-data.json

In the above example, the contents of the file initial-data.json will be loaded into the store named 'example'.

This file contains a JSON object, such as the following:

  "foo": "bar",
  "baz": {
    "qux": "corge"

Note that you can store child objects, but the top level keys must always be a string.

Preloading from inline data

If you have a small amount of data, or you don't want to use a separate file, you can provide the preload data inline within a configuration file using the preloadData key:

plugin: rest

    # this store is preloaded from inline data
        foo: bar
        baz: { "qux": "corge" }

In the above example, the items under preloadData block will be loaded into the store named 'example'.

You must provide an object with key/value pairs, such as that shown above, or in the JSON file below. Top level keys must always be a string.

Store implementations

Different store implementations exist:

GraphQL support

As well as the stores REST API described in this document, you can access and manipulate data using GraphQL.