API answers

Looking up an answer from a server.

Using an API answer, you can fetch a new answer from a server that returns JSON responses. This lookup can even use other answers collected with the flow as inputs or parameters.

Common uses of API answers include:

  • Finding the current price of an item.

  • Locating the closest store to a user, based on their zipcode.

  • Looking up an account ID based on a user's email.

You can also look up select choices from an API, defined directly on the select choices.

API answers behave just like any other answer: they can be used for conditions, templated into most text, and are sent to your analytics and integrations.

Doing a simple calculation with answers you already have present?

If you don't need access to data on a server, you can use a Calculated answer to perform a calculation directly within the form flow.

Adding an API answer

To add an API answer, go to Schema > API variables and click Add API variable...


Provide the URL of the endpoint you wish to hit in the API URL field. This will

You can use existing answers from the flow to template the API lookup URL with the standard templating syntax.

For example, if you ask the responder for their postal code in an answer with variable name user_zip, you can use that to look up store locations with a URL like https://example.com/api/stores?zip_code={{user_zip}}.


API answer HTTP requests come directly from the responder's browser, and so if your server enforces Cross-Origin Resource Sharing restrictions (CORS), you will need to whitelist flow.formsort.comandstudio.formsort.com (for testing within the studio) in the Access-Control-Allow-Origin response header.

Additionally, if you are using Custom domains to host your flows, you will need to whitelist those domains.

Alternatively, you can enable the * origin in the Access-Control-Allow-Origin header if you would like to disable CORS restrictions.

Authenticated endpoints

If your API endpoint is authenticated, we can query it through a proxy. This isn't yet available as self-serve, so chat us in order to set this up.

Variable type

Variable type sets the expected data type that we are expecting from the response: string, number, or boolean

Is array?

If Is array? is enabled, then we will expect the response to contain multiple answers.

Result processing

If your API returns a payload with a shape that isn't directly the desired variable type, you can process the result within Formsort, to avoid having to change the shape of your API responses.

For the below examples, consider a response payload for a list of stores.

// Sample JSON response body
address: "123 Main St",
isOpen: false,
address: "4 Back St",
isOpen: true,

JSON accessor

If the answer you with to access can be accessed directly with keys and indices, you can write out the path to the desired data with the JSON accessor.

For example, 0.address would return the address of the first result, which in the above example would be "123 Main St".

Mapping function

For more complex processing of results, you can write a mapping function using javascript, similar to a calculated answer's getter function body.

This function has an argument, res, which is the raw JSON object returned from the server. It should return the desired answer.

For example, if we'd like to access the address of the first open address from the response above, the mapping function would be:

const openStores = res.filter(function(store) { return store.isOpen });
if (openStores.length) {
return openStores[0].address;
return undefined;

... which would result in "4 Back st"

When are API lookups dispatched?

If an API answer has no dependencies (there are no templated answers within its URL), the API lookup will happen as soon as the flow loads.

If an API answer has dependencies, the API lookup will happen as soon as all of its inputs are defined, and will be re-run whenever those inputs change. If any of the inputs become undefined, the API answer will be cleared.

For more control over when the API lookup happens, you can set a condition for its evaluation with Is conditional?

Re-calculate on load

If an API answer was retrieved in a previous session, and the responder returns to the flow, the default behavior is not to re-fetch the answer.

To always fetch the answer on load, enable Re-calculate on load. This is useful for situations when calculated answers are not idempotent, meaning that repeated invocations do not result in the same result, such as answers depending on an API response that changes over time.

Awaiting responses

If there is a pending API answer lookup, and the user is trying to advance to a step that uses the resultant answer, a loading indicator will be displayed while they await the result of the lookup.

Avoiding the loading spinner

Consider interleaving steps that provide inputs for API answers with steps that contain static content, or content orthogonal to the API lookup.

That way, even if an API request is slow, it will not matter, as the user will be viewing other content while the request happens in the background.

Handling errors

If an API answer request fails, or returns an invalid response, the answer will be undefined, and the answer will be marked as failed.

You can use the Had a loading error condition operator on a group, step, or question to affect the logic of a flow based on a failed answer, for example to put up a custom error message, or provide the responder an alternative way forward.