Where the advanced techniques start
An expert grid is one whose solving path costs more than a hard grid's even after every cheap move has been made. In practice that means at least one point where you need a pattern that spans several units: an X-Wing, an XY-Wing, or occasionally a Swordfish.
Full pencil marks are worth it here
On easier grids, marking every cell wastes time. On an expert grid it is the only reliable way to see the patterns, because every one of them is defined by where a candidate can and cannot go across the whole board.
Enter your candidates with the notes button, keep them current as you place digits, and then look for structure: a digit that appears exactly twice in each of two rows, two cells that share a pair, a cell with only two candidates that sees two others.
Being stuck is part of it
There is no shame in a hint on an expert grid. The hint names the technique and explains the elimination in one sentence, then links to the guide for it. Reading why a move works while you are looking at the position it applies to is how these patterns stop being abstract.
Every expert puzzle here is still solvable by logic. If you cannot find the move, it exists — the generator would have thrown the grid away otherwise.
Common questions
What makes a Sudoku expert level?
A solving path that needs an advanced pattern — an X-Wing, XY-Wing or Swordfish — rather than just singles, locked candidates and pairs.
How many clues does an expert puzzle have?
Usually 22 to 26, though the count matters far less than the moves required.
Do expert puzzles require guessing?
No. Grids that cannot be solved with the site's technique list are discarded during generation, so a complete logical path always exists.
Which technique should I learn first?
The X-Wing. It is the most common of the advanced patterns and the easiest to spot once you know its shape.