Text Diff — Find the One Character That Differs
This compares two pieces of text and highlights the differences. Its value is concentrated in the cases where the difference is invisible: a trailing space, a non-breaking space that arrived via a paste from a document, a line ending convention, a zero-width character. All of them make two identical-looking strings unequal, and none of them are visible in an editor.
When it helps
For the moments where something should match and does not. A configuration value copied between environments that behaves differently. A signature that fails to verify because the payload differs by one character. A test asserting equality on strings that look the same on screen. Diffing them is the only way to see the difference, and once seen it is always obvious — which is what makes it worth reaching for early rather than after an hour of re-reading.
Worth running automatically
Comparison is exactly what automated checking is: a stored previous result compared against a current one. That is the whole basis of change detection, and it applies to anything you can retrieve — a configuration endpoint, a rendered page, a set of response headers, a third-party script. The interesting result is never the hundredth identical answer; it is the first one that differs, and having the diff means you are told what changed rather than that something did.
What you get out of it
Makes an invisible difference visible, which resolves the frustrating class of bug where two things that must match apparently do. The same operation, applied on a schedule, is change detection.