Free calculators, solvers & utilities — no sign-up, works offline
Thinker Toolbox is a collection of 19 free, browser-based tools for finance, energy, dates, cooking, puzzles, and design. No sign-up, no accounts, no data harvesting. Just open a tool and use it.
Every calculator runs entirely in your browser. Your financial data, search queries, and personal information never leave your device. PDF reports are generated locally. The word puzzles load a 168,000-word dictionary instantly and work offline.
Whether you're buying a house, checking your take-home pay, planning solar panels, or stuck on a crossword, there's a tool here that actually works without the clutter, pop-ups, and tracking that most free tool sites throw at you.
Private by design
All calculations run in your browser. No data is sent to any server. Your numbers stay on your device.
Works offline
Once you've visited a tool, it caches itself. No internet? No problem. Use it on the train, in a cafe, anywhere.
No sign-up required
No accounts, no email, no passwords. Just open and use. The way tools should be.
Mobile-first design
Big buttons, readable text, no pinching and zooming. Every tool is designed for your phone first.
UK-focused finance tools
Tax bands, National Insurance, stamp duty, SEG tariffs, Octopus Energy. All built for UK users, not US-centric approximations.
Instant results
No server round-trips. Everything calculates as you type. The word puzzles load a 168,000-word dictionary instantly.
First-time buyers: Use the mortgage calculator to work out monthly payments, stamp duty, and how much you can afford before you start viewing properties.
Employees checking their pay: The salary calculator shows exact take-home pay after tax, NI, student loans, and pension contributions for the current UK tax year.
Homeowners with solar panels: The solar calculator, SEG calculator, and battery optimiser help you understand your return on investment, compare export tariffs, and maximise your savings.
Puzzle enthusiasts: Stuck on a crossword, anagram, or Wordle? The word puzzle solvers find every matching word from a 168,000-word dictionary. The Scrabble finder scores every possible play from your rack.
Anyone who needs a quick calculation: Percentages, dates, tips, cooking conversions, colour palettes. All the little calculations that come up in daily life, without the clutter and tracking of ad-heavy sites.
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