# Nonces

In DNAnexus, a **nonce** is a string that uniquely identifies a request against the DNAnexus API. Using a nonce ensures that regardless of how many times a request is made, the result remains the same as a single successful request. This is particularly useful for handling network failures. If a response is dropped on its way back to the client, the client can reissue the request with the nonce, and DNAnexus API recognizes it as a previous request and returns an exact replica of the dropped response.

The nonce field is used primarily in API methods for project, data object, and job creation. Using a nonce with these API methods prevents a client from creating duplicate items when only one is intended. The API methods are as follows:

* [`/app/new`](/developer/api/running-analyses/apps.md#api-method-app-new)
* [`/app-xxxx/run`](/developer/api/running-analyses/apps.md#api-method-app-xxxx-yyyy-run)
* [`/applet/new`](/developer/api/running-analyses/applets-and-entry-points.md#api-method-applet-new)
* [`/applet-xxxx/run`](/developer/api/running-analyses/applets-and-entry-points.md#api-method-applet-xxxx-run)
* [`/file/new`](/developer/api/introduction-to-data-object-classes/files.md#api-method-file-new)
* [`/job/new`](/developer/api/running-analyses/applets-and-entry-points.md#api-method-job-new)
* [`/org/new`](/developer/api/organizations.md#api-method-org-new)
* [`/record/new`](/developer/api/introduction-to-data-object-classes/records.md#api-method-record-new)
* [`/workflow/new`](/developer/api/running-analyses/workflows-and-analyses.md#api-method-workflow-new)
* [`/workflow-xxxx/run`](/developer/api/running-analyses/workflows-and-analyses.md#api-method-workflow-xxxx-run)

As a nonce is a unique identifier of a request, the input used in a request must remain unchanged when retrying with a nonce. If any change is made to the input, the API considers it a separate and different request and throws an InvalidInput error. The nonce field must not exceed 128 bytes in a UTF-8 encoded string.

Nonces are designed for recovery and retry of dropped requests within a short time period. This behavior is guaranteed only for second requests made within one hour of the original request. After one hour, the second request may create a new object (as if no nonce was supplied).


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