What msclkid actually is
msclkid is the Microsoft Click ID, appended automatically when auto-tagging is enabled on a Microsoft Advertising account and someone clicks an ad on Bing or across the Microsoft network. Functionally it is the same idea as Google's gclid: a per-click token that lets conversions on the destination site be joined back to the campaign that paid for the visit.
What the value actually looks like
A real msclkid is a 32-character GUID, for example a1b2c3d4e5f67a8b9c0d1e2f3a4b5c6d, substituted into the destination URL as ?msclkid={msclkid}. Microsoft Advertising ships this switched on for every new account: auto-tagging of MSCLKID is enabled by default, and turning it off means unchecking "Add Microsoft Click ID (MSCLKID) to URLs to allow conversion tracking" under Campaigns > Settings > Account level options.
A worked example, decoded
Paste https://example.com/lp?msclkid=1a2b3c4d5e6f7a8b9c0d into the decoder above and it separates into the destination, https://example.com/lp, and one parameter, msclkid=1a2b3c4d5e6f7a8b9c0d. The value carries no information on its own. Its whole job is to be sitting on that landing page hit so the Universal Event Tracking (UET) tag installed there can read it and attach it to whatever conversion fires next.
Why you see it less often
Simply because fewer clicks originate on Bing than on Google, so it turns up less in the wild. That does not make it less consequential for anyone actually running Microsoft campaigns, where it is the backbone of conversion tracking in exactly the same way.
Common mistakes
- Assuming msclkid works without a UET tag. Auto-tagging appends the parameter regardless of what the destination site does. Nothing reads it unless that site has Microsoft's UET tag installed, so a site with auto-tagging on and no UET tag ends up with a URL carrying an unused parameter.
- Treating it as interchangeable with gclid. Both do the same conceptual job for different platforms, but a redirect rule or script written to recognise one by name will silently ignore the other unless it checks for both explicitly.
- Not realising it is already on. Auto-tagging of MSCLKID ships enabled by default on every new Microsoft Advertising account. Most accounts are generating it whether or not anyone has ever opened that settings page.
Is it safe to remove?
For visitors, yes. For advertisers it needs to survive the entire path from ad click to conversion. It is a good habit to check your redirect chain preserves it, since the failure mode is silent: campaigns simply appear to underperform and nothing in the interface tells you a parameter was dropped along the way.