Checking Gate Post Plumb and Alignment
Two Directions, Two Different Problems
A post can lean along the line of the fence or across it, and the two mean different things. Leaning across the line, away from or toward the gate, is the classic footing failure caused by the leaf's weight rotating the post. Leaning along the line usually points at ground movement rather than at load. Checking only one direction, which is what most people do, misses half of what a level would tell you.
Measure the Post, Not the Gate
A gate can be trued at the hinges to compensate for a post that is out, so a leaf that hangs correctly proves nothing about the post underneath it. Put a spirit level directly against the post itself, on two adjacent faces. This is a thirty second measurement and it is the one that answers the question.
Check the Gap, Then Check It Again Later
The gap between the leaf and the post, or between two leaves at the meeting point, is a sensitive indicator. What matters is not the number but the change in it. Measuring the gap at the top and at the bottom and writing both down gives a baseline. If the top gap is opening relative to the bottom over subsequent checks, the post is rotating, and you now know it is progressive rather than historic.
Distinguishing Old Movement From Active Movement
This is the distinction that decides what to do. A post that settled once, years ago, and has been stable since can often be lived with or corrected at the hinges. A post still moving will undo any adjustment made to it, and the work belongs at the footing. Only repeated measurement separates the two, which is the argument for keeping a simple written record rather than relying on an impression.
What the Ground Says
While the level is out, look at the base of the post. A crack radiating in the surrounding slab, a gap opening between footing and soil, or ground that is noticeably softer on one side all corroborate a measurement. On sandy coastal ground, water is usually the mechanism, so look at where rain runs at the entrance and whether it is being directed away from the footing or straight at it.