Quick Summary
The HTTP 400 Bad Request error indicates that the server cannot understand or process the request sent by the client due to a client-side error. This typically means something is wrong with the request itself, such as incorrect syntax or invalid parameters.
Common Causes
- Invalid Request Syntax: The URL or HTTP request line may contain illegal characters, spaces where they are not allowed, or other syntactical errors. Browsers can sometimes automatically encode or decode URLs leading to unforeseen problems.
- Malformed Request Body: The body of the HTTP request (e.g., the data sent during a POST or PUT request) might be improperly formatted. This is particularly common with JSON or XML data, where a missing bracket or tag can cause a parsing error on the server side.
- Incorrect Request Headers: Request headers may be missing, contain invalid information, or be in the wrong format. Common issues include incorrect Content-Type headers or missing required authentication headers.
- Invalid Cookies: A browser cookie might be corrupted, expired, or set incorrectly, causing the server to reject the request. Cookies can also become too large, exceeding the server's limits.
- Request Too Large: The server may have a limit on the size of the request it will accept. This limit can apply to the URL, the request headers, or the request body (especially during file uploads).
Step-by-Step Fixes
Method 1: Check the Request URL
Step 1: Carefully examine the URL in your browser's address bar or within your application's code.
Step 2: Look for any typos, missing characters, extra spaces, or invalid symbols. Ensure that the URL is properly encoded and that all required parameters are present.
Step 3: Pay special attention to characters like spaces, which should be encoded as %20. If passing parameters, verify that the syntax is correct (?param1=value1¶m2=value2).
Method 2: Validate Request Body/Payload
Step 1: If you're sending data (e.g., in a POST or PUT request), double-check the format of the data you're sending.
Step 2: For JSON data, use a JSON validator tool to ensure that the JSON is correctly formatted. Similarly, for XML data, use an XML validator.
Step 3: Verify that all required fields are present and that the data types are correct (e.g., numbers are numbers, dates are in the correct format).
Method 3: Clear Browser Cookies and Cache
Step 1: Clear your browser's cookies and cache. The specific steps vary depending on your browser, but you can usually find these options in the browser's settings or preferences menu.
Step 2: Restart your browser after clearing the cache and cookies.
Step 3: Try sending the request again to see if the problem is resolved. Corrupted or outdated cookies are a common cause of 400 errors.
Method 4: Inspect Request Headers
Step 1: Use your browser's developer tools (usually accessible by pressing F12) or a network analysis tool like Wireshark to inspect the HTTP request headers.
Step 2: Verify that the Content-Type header is set correctly for the type of data you're sending (e.g., application/json for JSON data, application/x-www-form-urlencoded for form data).
Step 3: Check for any other required headers, such as Authorization headers for authentication. Ensure that the header values are correct and properly formatted.
Method 5: Reduce Request Size
Step 1: If you're uploading a file or sending a large amount of data, try reducing the size of the request.
Step 2: For file uploads, compress the file before uploading. For large data payloads, try breaking the data into smaller chunks or streaming it to the server.
Step 3: Check if the server has a limit on the size of requests. If so, adjust your request accordingly. You may need to contact the server administrator to increase the limit.