What is the maximum length of url MS servers accepts before throwing error 400

Hi Aymen,

Thank you for reaching out.

Currently, there does not appear to be any official Microsoft documentation specifying the maximum supported length of a Microsoft Forms pre-filled URL. Therefore, a Forms-specific maximum cannot be confirmed from the publicly available documentation. The actual behavior may vary depending on factors such as the browser, URL encoding, intermediary services, and how Microsoft Forms processes the request.

As a practical guideline, keep the complete encoded URL below approximately 2,000 characters, since long text and special characters can increase the URL length after encoding. Please consider pre-filling only short fields and testing the link in the intended browsers.

I hope you found the answer helpful. Should you have any further questions, please feel free to reach out and let me know. I'll be happy to help.

Thank you for your patience and understanding. Wishing you a great day ahead.

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the 2048 is the max length of the url (base plus query string). so the length of the base url matters, plus any character encoding which increases the length of a query string value. there are the "&" and "=" separators for each field, so the number of fields effects the max length. the length of the field names will also have an effect.

all this means is the length is pretty dynamic.