A query string is the part of a URL after ? that passes data to the server. Format: key=value, multiple params separated by &.
Common Uses:
• UTM tracking — track traffic sources in Google Analytics
• API requests — pass filtering, sorting, and pagination to REST APIs
• Referral links — share referral codes and source information
• Page state — preserve filter selections and search terms
Encode or decode with the URL Builder in three steps:
Special characters (spaces, Chinese, &, =, etc.) are URL-encoded automatically (space becomes %20). Use "Copy Encoded URL" for the fully encoded version.
UTM parameters can create duplicate content issues. Use Google Search Console's URL parameter tool to set handling rules, or restrict UTM-parameter URLs in robots.txt.
There's no hard limit, but browsers and servers typically limit total URL length to 2048-8000 characters. Keep it concise and remove unnecessary params.