Snap Markup
iOS and Android · best for plain, fast markup. Arrows, text, shapes, blur, crop — no backgrounds, no styling, no learning curve. If all you ever do is circle the broken thing and send it to a developer, this does that and nothing else.
ScreenCandy
iOS and Android · best for compose, mark up and redact in one pass. Share a screenshot to it and it opens already composed: 30 built-in looks, 6 background modes, 11 CandyMark tools, and blur or pixelate redaction flattened into the export. Everything is on-device — no account, no upload, no analytics. It does not stitch, it does not build device mockups, and it does not take the screenshot for you.
The editor already on your phone
iOS and Android · best for free and instant. iOS Markup and the Android screenshot editor are one tap from the capture and cost nothing. They crop, draw and add text. iOS Markup cannot blur at all, and neither adds a background — which is the whole reason the rest of this list exists.