Why it matters
Duplicate URLs split your ranking signals across copies and let engines pick a version you didn't intend, sometimes a parameter-riddled one. Canonicals consolidate the credit onto the address you want to rank.
How it works
Each page carries a tag naming its canonical self; variants point at the original. Engines treat it as a strong hint, folding duplicate signals into the named URL. Most CMSes and frameworks handle it automatically once configured: misconfiguration is what to watch for.
What to do about it
Spot-check your key pages: view source, find the canonical tag, confirm it points where you'd expect. Do the same after any migration or platform change: that's when canonicals quietly break.
