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405+ free online tools for PDF, images, SEO, developers, color, and productivity. Fast, browser-based, and private — no signup, no installs, no limits. Search above or browse by category below.
Total tools405Available free tools
Categories15Active categories
Most usedCSV to ExcelPopular right now
Recently addedInterval Music RepeaterNewest tool
Image Watermark Add Remove
Add text or logo watermarks to your own images, or cover/undo a region privately in your browser — free image stamp tool.
Audio Converter
Free online audio converter — convert MP3, M4A, OGG, or FLAC to WAV in your browser. Change sample rate and channels privately with no upload or signup.
Measurement Uncertainty Calculator
Combine and propagate measurement uncertainty with root-sum-of-squares (RSS). Add, subtract, multiply, or divide values with ± uncertainties, convert percent uncertainty, and compute expanded uncertainty U = k·u. Free, instant, browser-based.
Fluid Velocity Calculator
Calculate fluid velocity from volumetric flow rate and cross-section geometry. Modes: circular pipe, rectangular channel, annulus, known area, continuity (pipe reducer), and velocity unit converter. Reynolds number and flow regime. Metric and imperial units. Free, browser-based.
DNA Reverse Complement
Get the reverse complement of a DNA or RNA sequence — A↔T/U, G↔C with GC content and FASTA support. Free, instant, browser-based.
Sketchbook AI
Plan and generate KDP-ready coloring book pages—concept plan, line-art images, reorder, and export PDF/JSON with your own API key.
Spelling Practice
Free spelling practice tool — see a definition or scrambled letters and type the correct spelling. Instant correct/incorrect feedback.
Heart Rate Zone Calculator
Calculate heart rate training zones with Karvonen or % max HR — 3 or 5 zones from age, resting HR, and max HR formulas. Free, instant, browser-based.