What is HTTP 412 Status Code (Precondition Failed)?

Reliqus Marketing

08 April 2024

HTTP Status Codes
By Ankit Bhatia
Founder & CEO

As a website owner or developer, encountering HTTP status codes like the 412 error can be more than just a minor inconvenienceit can be a roadblock in your project’s progress

The “Precondition Failed” message accompanying a 412 Status Code may initially appear cryptic and daunting. 

However, there’s no need to worry—Reliqus Consulting is here to illuminate this topic and guide you through understanding and resolving this issue.

In this blog post, we will explore the meaning of the 412 status code, clarify why this error occurs, and explain how to navigate it easily, ensuring smooth communication between servers and clients.

What is the HTTP 412 Status Code?

The HTTP 412 status code, also known as “Precondition Failed,” is a response from a server indicating that one or more conditions specified by the client in the request headers were not met. 

These conditions are typically used to ensure data consistency and integrity during client and server transactions. 

When a server returns a 412 status, it signifies that the preconditions in the request headers, such as “If-Match,” “If-None-Match,” “If-Modified-Since,” or “If-Unmodified-Since,” failed, preventing the requested operation from being carried out.

412 PRECONDITION FAILED Source: RFC7232 Section 4.2

412 Code References

Different programming languages and frameworks have constants or symbols representing HTTP status codes, including 412. 

Here are some references:

Rails HTTP Status Symbol :precondition_failed

Go HTTP Status Constant http.StatusPreconditionFailed

Symfony HTTP Status Constant Response::HTTP_PRECONDITION_FAILED

Python2 HTTP Status Constant httplib.PRECONDITION_FAILED

Python3+ HTTP Status Constant http.client.PRECONDITION_FAILED

Python3.5+ HTTP Status Constant http.HTTPStatus.PRECONDITION_FAILED

Each of these references serves the same fundamental purpose: to provide a clear, standardized way to handle the specific scenario where the server does not meet a precondition set by the client. 

By understanding how different languages and frameworks refer to the 412 status code, developers can better navigate and implement HTTP status code handling in their projects, ensuring that web applications behave correctly and efficiently in response to various client-server interactions.

When is a 412 Status Code Used?

An HTTP 412 status code is typically used in situations involving requests that are neither HTTP method HEAD nor HTTP method GET. It signifies that the request cannot be processed because one or more conditions, as specified by the client, have not been met. 

This failure prevents the server from retrieving the resource in the expected format or state the client anticipated. The 412 preconditions failed error message directly indicates this failure, highlighting the necessity of satisfying certain preconditions before a request can be successfully fulfilled.

How to Use 412 HTTP Status Codes for a Website?

Web developers leverage the 412 HTTP status code for scenarios requiring specific configurations for a file’s delivery. It indicates “Precondition Failed,” signifying that the browser client has not established the required configurations. 

This response code enables clients to set preconditions on the current state of a resource, ensuring that the request method is only executed if the resource’s state matches expectations. It is a crucial tool for maintaining data consistency, preventing actions from being performed on resources in an unintended state.

HTTP 412 Status Code Example

To provide a clearer understanding of how the 412 Precondition Failed status code works in practice, let’s consider a practical example.


Consider a scenario where a client is attempting to leave a comment on an online article. The client wants to ensure their comment is added only if the article has not been updated since they last read it. 

If the article has been modified, it responds with a 412 precondition failed status error, indicating the client’s request cannot be fulfilled due to its updated state.


POST /examplearticle/update?postid=123&task=reply HTTP/1:1

Host: www.example.com

If-unmodified-since: 13 March 2023 0:00:00 GMT

Content-type: text/plain

Content length: 30

<message body from client>


HTTP/1:1 412 Precondition Failed

Content type: text/plain

Content length: 60



<title> Article Update Error <title>



<p> This article has been updated since you recorded your comment, so your response will not be posted.&lt>;p>



The Common Causes Of The 412 Precondition Failed

The 412 Precondition Failed status code occurs in specific scenarios where the server does not meet the preconditions set by the client in the request headers. Understanding these causes can help diagnose and fix issues that lead to this error. 

Here are the common triggers:

Conditional Headers:

Clients may set conditional headers in their requests to ensure that the operation proceeds only if certain conditions are met. These headers include “If-Match,” “If-None-Match,” “If-Modified-Since,” or “If-Unmodified-Since.” 

A mismatch between the client’s expectations (based on these headers) and the current state of the resource on the server triggers a 412 response. 

ETag Inconsistency:

ETag, or Entity Tag, is a mechanism to identify a specific resource version. A 412 error might occur if the client’s request includes an “If-Match” header with an ETag value that does not match the resource’s current ETag value. 

This inconsistency indicates that the resource has been altered, preventing the server from fulfilling the request as intended.

Timestamp Mismatch:

When clients use headers like “If-Unmodified-Since,” they expect the resource to remain unchanged since a specific timestamp. If the server detects that the resource has been modified after the provided timestamp, it will return a 412 error. This situation usually arises when trying to ensure that updates or modifications are made based on a resource’s latest and unaltered version.

Each of these causes points to a discrepancy between the client’s expectations (based on the resource’s state when it was last accessed or modified) and the resource’s current state on the server. Handling these scenarios requires proper client request management and server-side resource state tracking.

7 Best Practices To Prevent The 412 Precondition Failed Error

Preventing the 412 Precondition Failed error involves understanding its causes and implementing strategies that minimize its occurrence. 

Here are seven best practices that developers and site administrators can follow to reduce the likelihood of encountering this error:

  1. Clear The Browser’s Cookies And Cache

Instruct users to regularly clear their browser’s cache and cookies. This ensures they are not working with outdated resources that could trigger a 412 error due to ETag or timestamp mismatches.

  1. Verify The Preconditions

When implementing client-side logic, ensure that any preconditions (such as ETags or timestamps) sent in request headers are accurate and reflect the current state of resources. This minimizes the risk of precondition failures.

  1. Review The Conditional Headers

Carefully manage conditional request headers (`If-Match`, `If-None-Match`, `If-Modified-Since`, and `If-Unmodified-Since`) to ensure they are used appropriately and only when necessary. Incorrect usage can lead to unintended 412 errors.

  1. Update The ETag

Implement robust ETag generation and validation mechanisms on the server. Ensure that every time a resource is modified, its ETag is updated accordingly. This helps maintain consistency between client and server views of the resource.

  1. Refresh Timestamps

For resources that rely on timestamps to manage updates and caching, ensure the server provides accurate `Last-Modified` dates. Similarly, clients should use these timestamps appropriately in the `If-Modified-Since` and `If-Unmodified-Since` headers.

  1. Improve The Error Handling Mechanism

Develop comprehensive error-handling mechanisms on both the client and server sides. When a 412 error occurs, provide clear feedback to the user or system about the cause and possible steps to resolve it. For example, instructions to refresh the resource or clear the cache.

  1. Test And Monitor

Regularly test and monitor your application for 412 errors. Use tools to log and analyze when and why these errors occur. Continuous monitoring helps identify patterns or specific scenarios frequently triggering the error, allowing for proactive adjustments.

Implementing these best practices can significantly reduce 412 Precondition Failed errors. By ensuring that your application correctly handles conditional requests and maintains up-to-date resource states, you can improve your web services’ reliability and user experience.

Which HTTP Method is used with 412 HTTP Status Codes?

Multiple HTTP methods are utilized with the 412 HTTP Status Code, each serving a specific communication function between the client and the server. Among these methods, the GET and HEAD methods are prominently used.

Let’s delve into how these methods interact with the 412 status code:

GET HTTP Method:

The GET method is a standard HTTP method primarily associated with the 412 HTTP Status Code. This method requests a representation of a specific resource, adhering to the principle that GET requests should only retrieve data without causing any side effects on the server’s state. 

Combined with the 412 Status Code, it indicates that the server understands the request but refuses to fulfill it due to unmet preconditions in the request headers, specifically relating to the resource accessed through a GET request.


The HEAD HTTP method is notably used with the 412 HTTP Status Code. This method functions similarly to the GET HTTP method, a standard request method for retrieving data from a server. 

However, the HEAD method is unique because it requests the headers that would be returned if the GET HTTP method were used without returning the response’s body. 

This makes the HEAD method particularly useful with the 412 status code, as it allows clients to check the resource’s current state or validity based on header information before downloading the entire resource.

What are the Related HTTP Response Headers with 412 HTTP Status Code?

Two key headers are integral to the functioning of conditional requests that can lead to a 412 Precondition Failed response: the If-Unmodified-Since HTTP Header and the If-None-Match HTTP Header.

If-Unmodified-Since HTTP Header: 

This header makes a request conditional by specifying that the server should only send or accept the requested resource if it has not been modified since the date provided in the header. 

It is particularly relevant for non-safe methods like POST, which modify server data. If the requested resource was modified after the specified date, a 412 Precondition Failed error will be returned, indicating that the client’s precondition was not met.

If-Non-Match HTTP Header: 

This header makes the request conditional based on the resource’s entity tag (ETag). When this header is used, the server is instructed to return a 200 status for GET and HEAD methods only if the resource’s ETag does not match any of the provided ETag values. 

For methods other than GET and HEAD, the request will only proceed if the existing resource’s ETag does not match any of the ETags listed in the If-None-Match header. This mechanism helps ensure that clients are working with the correct versions of resources.

How 412 Status Code Affects SEO?

The impact of HTTP status codes on SEO is essential for web admins and developers. While the 412 Precondition Failed status code is primarily associated with conditional requests and server-client data consistency, its occurrence and handling can indirectly influence a website’s search engine optimization (SEO) in several ways:

Crawl Efficiency

Search engines allocate a crawl budget for each website, the number of pages a search engine bot will crawl and index within a given timeframe. 

Frequent 412 errors could potentially waste a portion of this budget, as search engines might attempt to access resources that are not adequately responding due to precondition failures. 

Ensuring efficient server responses and minimizing unnecessary 412 errors can help optimize the use of your crawl budget.

User Experience

While direct interactions with 412 status codes are more common in API and web application development than in regular user browsing, consistent errors, including 412, can degrade the user experience. 

Poor user experience can increase bounce rates and reduce the time spent on the site, which are factors that search engines consider when ranking websites.

Indexing Issues

If critical resources on a website consistently fail to load due to misconfigured conditional requests, leading to 412 errors, the content’s visibility and indexability could be affected. 

Ensuring that web resources are accessible and correctly configured for conditional requests can prevent such indexing issues.

Site Quality Signals

Frequent errors, including 412 Precondition Failed responses, can affect a website’s overall quality and reliability as perceived by search engines. High error rates may be interpreted as signs of a poorly maintained or unreliable site, which could negatively impact search rankings.

To mitigate potential negative SEO impacts, handling 412 Precondition Failed responses is crucial. This includes configuring servers and applications to minimize unnecessary precondition failures, monitoring for frequent errors, and ensuring that web content is accessible and correctly indexed by search engines. 

Which Browsers are Compatible with a 412 Response Code?

All modern web browsers are designed to handle HTTP status codes, including the 412 Precondition Failed response. This ensures that web applications can implement and rely on conditional requests as part of their logic, knowing that the behavior will be consistent across different client environments. 

Here’s a quick overview of browser compatibility:

Chrome: YES

Edge: YES

Firefox: YES

Internet Explorer: YES

Opera: YES

Safari: YES

WebView Android: YES

This compatibility plays a crucial role in web development. It allows developers to design complex web applications that rely on HTTP conditional requests to manage resource state and caching more efficiently. Regardless of the user’s browser choice, the application’s logic for handling 412 Precondition Failed errors and other conditional responses will operate consistently.

What are the other Similar Status Codes to 412 HTTP Status Code?

Understanding HTTP status codes similar to 412 can help developers handle client-server interactions and error handling better. 

Here are some status codes related to 412 Precondition Failed, highlighting their specific use cases and how they differ from 412:

411 Length Required Vs. 412 Precondition Failed

411 Length Required:  This status code indicates that the server refuses to accept the request without a defined Content-Length header. Unlike 412, which is about preconditions on resource states, 411 focuses on the technical requirement of specifying the size of the request’s body.

413 Payload Too Large Vs. 412 Precondition Failed

413 Payload Too Large: This response code is returned when a request is more significant than the server can process. Unlike 412, 413 deals with the physical size of the request rather than conditions applied to the requested resource.

414 URL Too Long Vs. 412 Precondition Failed

414 URL Too Long: This code is used when the URI provided by the client is too long for the server to handle. It’s related to the limitations of the server in processing long URLs rather than the conditional failure of requests, which 412 signifies.

415 Unsupported Media Type Vs. 412 Precondition Failed

415 Unsupported Media Type: This status code is sent when the request entity has a media type that the server or resource does not support. For example, a client uploads an image in a format not supported by the server. This status code concerns media type compatibility rather than the conditional mismatches that trigger a 412.

Each status code provides specific feedback about why a server cannot fulfill a request, guiding developers in resolving request formatting, size, and conditions issues. Understanding the nuances of these related status codes enables better error handling and more resilient web application development.


In conclusion, while HTTP status codes might initially seem daunting, they are essential tools in the web developer’s toolkit. With the insights and strategies this guide shares, we hope you feel more prepared to tackle the 412 Precondition Failed status code and any other HTTP status codes you may encounter in your web development journey. 

At Reliqus Consulting, we’re here to help you turn these challenges into opportunities for growth and improvement, ensuring your web projects succeed now and in the future. Our expertise extends to diagnosing and resolving issues like the 412 Precondition Failed error, ensuring your web applications communicate efficiently and effectively. 

Remember, every status code, including 412 Precondition Failed, is an opportunity to enhance your website’s communication with its users. By effectively understanding and addressing these codes, you can ensure that your site remains accessible, functional, and ready to serve your audience’s needs.

Frequently Ask Questions (FAQs)

Before we wrap up, let’s address some frequently asked questions that might arise as you navigate the complexities of the 412 Precondition Failed status code. These insights aim to clarify common points of confusion further and provide you with actionable knowledge to tackle this error efficiently.

How do I Fix Error 412?

To fix a 412 error, ensure your request headers are correct and meet the server’s preconditions. This may involve adjusting conditional headers or verifying the state of the resource you’re attempting to access.

What is the Difference Between the 412 and 400 Status Codes?

A 400 status code indicates a general bad request error, suggesting the request cannot be processed due to client error. In contrast, 412 indicates that the request’s preconditions are unmet.

What is Error Code 412 on Google?

Error code 412 on Google typically indicates a “Precondition Failed” error, suggesting a request to a Google service failed because certain conditions were unmet.

What Does Precondition Fail to Mean?

“Precondition failed” means that the server cannot fulfill the request as the preconditions specified by the client in the request headers were not met.

How to Check 412 HTTP Status Code?

You can check for a 412 HTTP Status Code using the web browser network tab and developer tools for every resource the client uses.

Ankit Bhatia

Founder & CEO at Reliqus

With 12+ years of experience building a web presence for 300+ businesses, Ankit understands how businesses can use technology to increase revenue.

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