A black box over text does not redact a PDF
Why drawing a rectangle over a name leaves the name in the file, how to check whether a document you have been sent is leaking, and what actually removes text.
Guides
Answers to the questions that bring people to a converter in the first place, written properly rather than assembled from keywords.
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Why a hydrating page eats the visitor's first click
Lazy hydration drops the gesture that triggered it, and assigning input.value while claiming a server-rendered node collapses the caret. Both fail silently, and neither shows up in a Lighthouse audit.
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Why timestamp converters get nanoseconds wrong
Nanosecond timestamps are larger than JavaScript can hold exactly, digit-counting only identifies seconds between 2001 and 2286, and adding a time to a date changes which instant it means.
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Why base64 tools break on café, 你好 and emoji
The btoa trap, why "InvalidCharacterError" is the good outcome, and how to encode text of any language to base64 correctly in JavaScript.
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The PDF /Rotate flag, and why your page number lands in the wrong corner
A PDF page has two coordinate spaces — the one it is stored in and the one you see. On a rotated scan they differ by 90 degrees, and anything you draw goes in sideways.
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Why two contrast checkers give you different numbers
The linearisation step most implementations skip, why it moves mid-tones across the AA pass line, and how to tell which of two disagreeing tools is right.
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Does converting an image remove its EXIF data?
Usually yes, and usually without telling you. What EXIF holds, which operations destroy it, why preserving it badly is worse than losing it, and how to decide which you want.
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How to reduce image file size without losing quality
Three methods, ranked by how many bytes they save and what they cost you in quality. The one that saves the most is the one most people skip.
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JPEG vs PNG — which should you use?
A side-by-side comparison, the reason the two behave in opposite ways on photos and screenshots, and the three cases where the obvious rule is wrong.
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What is a WebP file, and how do you open one?
A modern image format that every browser reads and a lot of desktop software still refuses. Where it came from, why you keep meeting it, and what to do with one.
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What DPI do you need for printing?
What to use for photos, posters and banners, why the number depends on viewing distance, and why an image tagged 300 DPI can still print blurry.
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Why is my photo file so large?
Almost always the megapixels, occasionally the format, and sometimes a setting nobody told you was on. How to tell which, and what each one is worth fixing.
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Which image format should you actually use?
JPEG, PNG, WebP, AVIF and HEIC compared by what they are for rather than by specification. A decision you can make in about thirty seconds.
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Why iPhone photos will not open on Windows
HEIC is why iPhone photos arrive as files Windows refuses to open. What the format is, and four ways to fix it — including the one that stops it recurring.