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412 Precondition Failed: What Is It & How To Fix?

While browsing the internet, you may see some error messages displayed to inform you that your request cannot be completed and leave you confused. The HTTP 412 Precondition Failed Status Code is one of these messages.

This post will examine the meaning behind the 412 Precondition Failed Status Code error, find its causes, differentiate it from other status codes, and learn several possible solutions for resolving it.

Table of Contents

412 Precondition Failed Meaning

The HTTP 412 Precondition Failed status code is part of the HTTP under the 4xx response category, which is a client error. It indicates that the server is rejecting the client’s request since one or more preconditions determined in the request headers are not met. Owing to this failure, the server cannot complete the client’s request.

Such preconditions may include specific headers, tags, and other requirements which must be satisfied before the request can be successfully processed on the server. In detail, the specific headers of conditional requests should be an “If-Match,” “If-None-Match,” “If-Modified-Since,” or “If-Unmodified-Since.”

If a client sends an “If-Match” or “If-Unmodified-Since” request and the server finds that their precondition has not been fulfilled, the client will receive a 412 Precondition Failed error. For instance, if a client posts data in a POST request method with an Etag that is different from what is currently stored in the resource for some reason, a client will receive this response code.

412 Precondition Failed error message

The Common Causes Of The 412 Precondition Failed

In most cases, 412 Precondition Failed error occurs when a server is unable to process the request due to certain preconditions not being met. The followings are some common causes that you can take a look at:

  • Conditional headers: The conditional headers include “If-Match,” “If-None-Match,” “If-Modified-Since,” or “If-Unmodified-Since.” These headers are used to determine conditions that must be fulfilled for the requested resource to be provided. The server will respond with a 412 Status Code when one of these conditions is not met.

  • Etag inconsistency: Etags are unique information associated with a resource on the server. If a client sends an “If-Match” header with an inaccurate or obsolete Etag, the server determines the precondition failed and returns a 412 status code error.

  • Timestamp mismatch: Timestamps are relied on by the headers like “If-Modified-Since” and “If-Unmodified-Since” to find out whether a resource has been modified since the last request. If the timestamp that has been provided does not match the timestamp of the server, the precondition fails, leading to a 412 Status Code error

The common causes of the 412 Precondition Failed error

Similarities Between HTTP 412 Precondition Failed And Other Status Code Errors

411 Length Required Vs. 412 Precondition Failed

The HTTP Status Code 411 Length Required demonstrates that the server has refused the client’s request since it does not include a Content-Length header field. This error is similar to the HTTP 412 client error response. For a correct execution on the server, it is necessary to specify that specific field in all requests.

Read more: 411 Length Required: What Is It & How To Fix?

413 Payload Too Large Vs. 412 Precondition Failed

HTTP 413 Payload Too Large Status Code or previously called “Request Entity Too Large” indicates that the client’s request exceeds the server’s limitations. Thus, its connection will be closed. This status code signals a client error response equivalent to HTTP Status Code 412.

414 URL Too Long Vs. 412 Precondition Failed

HTTP 414 URL Too Long Status Code indicates that the server will reject if the client sends the too-long URL request. The situation is similar to the HTTP status code 412, which is the type of client error response.

415 Unsupported Media Type Vs. 412 Precondition Failed

415 Unsupported Media Type HTTP Status Code indicates that the server or resource will decline the request with the media format of the information it does not support. This error resembles HTTP Status Code 412, which also signals client submission issues.

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    7 Best Practices To prevent The 412 Precondition Failed Error

    To prevent the occurrence of the 412 Precondition Failed error, you should implement the best practices that make sure that the handling of preconditions is proper and try to reduce the likelihood of encountering this error. The following actions are to consider:

    1. Clear The Browser’s Cookies And Cache

    Check that the relevant caches are cleaned and updated if caching is involved. This ensures that outdated content is not served and there is no potential conflict with the preconditions. Remove all cache entries associated with the requested resource to ensure the server retrieves its latest version.

    2. Verify The Preconditions

    Verify that the current state of the resource on the server is compatible with the preconditions specified in the request headers. Double-check timestamps, Etag, and other conditions to ensure accuracy. If these preconditions are obsolete or inaccurate, update them to reflect this state of affairs.

    3. Review The Conditional Headers

    Check the conditional headers sent in the request, which are “If-Match,” “If-None-Match,” “If-Modified-Since,” or “If-Unmodified-Since.” Make sure that the values are accurate, as well as consistent with server expectations. Update them as soon as possible if headers are incorrect or outdated.

    4. Update The Etag

    You must regenerate an Etag value for the resource you are requesting and update it to both your server and client when a 412 error occurs due to a mismatch of this element’s values. This ensures that there will be no precondition failure in the subsequent requests, including the correct Etag value.

    5. Refresh Timestamps

    If a timestamp mismatch causes the 412 error, update it in the request headers to reflect the current time or the server’s last known modified time. It ensures that this condition is evaluated accurately by the server.

    Best practices to prevent 412 Precondition Failed error message

    6. Improve The Error Handling Mechanism

    In order to give users a clear and informative error message, make the error handling mechanism more efficient. It would help them to understand the reason for the error and offer advice on how it could be resolved. Users may be assisted in updating requests according to the correct preconditions with clearer instructions.

    7. Test And Monitor

    After implementing the fixes, you can thoroughly test the application to ensure that the 412 Precondition Failed error will no longer occur. To identify and correct recurring errors immediately, monitor server logs and error reports.


    The 412 Precondition Failed status code is a client error as well as a signal between clients and servers. This indicates that one or more of the specified conditions has failed, and the server will not complete the request.

    Developers and administrators need to understand this status code to solve problems caused by Conditional Requests, browser cache, or Etags. You will be able to enhance the user experience and ensure a secure data flow between clients and servers in the web applications by complying with best practices and properly handling the 412 Status Code.

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