Guides
The questions behind the tools: what a form actually wants, why a file is the size it is, and what changes when you make it smaller. Written for India, where most of these forms are.
For the developer tools
All developer tools- How to check an IMEI number, and what the check can and cannot proveAn IMEI has 15 digits: an 8-digit TAC, a 6-digit serial and 1 Luhn check digit. Work the check by hand, and see why it cannot show a phone is stolen.Updated on 2026-10-15
- How to check whether a card number is valid, and what valid does not meanThe Luhn check worked on 4242 4242 4242 4242: the digits total 80, ending in 0, so it passes. Plus scheme and length checks, and why valid is not real.Updated on 2026-10-15
- Test data that cannot reach a real person, built safe on purposeWhy fixtures use example.com, RFC 5737 IP ranges, gateway test cards and seeds, and the one gap: a random Indian phone number may belong to someone.Updated on 2026-10-15
- How a TOTP code comes from a setup key and the time, worked through step by stepA 2FA code is HMAC-SHA1 of the setup key and the 30-second step, cut to 6 digits. The RFC 6238 test key at 59 seconds gives 287082, worked out here.Updated on 2026-10-15
- What your user agent says about you, and what it gets wrongA user-agent string names 5 things: browser, engine, OS, device and bot. Read Chrome on Windows part by part, and why it cannot tell Windows 10 from 11.Updated on 2026-10-15
- DNS leak test - what a browser can check, and how to check the rest in one commandA browser page cannot see which DNS server your device asks. How to find it with one nslookup command, and the IP and WebRTC checks that go with it.Updated on 2026-10-06
- How to check SPF, DKIM and DMARC for a domain, and fix the common faultsWhat SPF, DKIM and DMARC each prove, how to look them up, the 10-lookup SPF limit, Gmail's bulk-sender rules, and rolling DMARC from none to reject.Updated on 2026-10-05
- How to decode a JWT and check whether it is validA JWT is three Base64URL parts. How to read the header and claims, check exp, nbf, iss and aud, verify the signature, and why decoding is not verifying.Updated on 2026-10-05
- How to convert JSON to CSV, and CSV back to JSON, without losing dataHow nested JSON becomes CSV columns, what happens to arrays, why Excel mangles IDs and long numbers, and how to turn a CSV back into JSON safely.Updated on 2026-10-05
- How to open a Markdown (.md) file, read it formatted, and turn it into HTMLA .md file is plain text with formatting marks. How to open one on Windows, Mac or a phone, see it formatted, and convert Markdown to HTML or PDF.Updated on 2026-10-05
- How to read a Unix timestamp, in seconds or milliseconds, in your time zoneA Unix timestamp counts seconds from 1 January 1970 UTC. How to tell seconds from milliseconds by the digits, convert to IST or any zone, and avoid 2038.Updated on 2026-10-05
For the file tools
All file tools- Exam form photo and signature size in India, and how to hit it exactlyThe photo and signature sizes Indian exam portals ask for, in KB and in pixels, and how to reach them without the picture turning to mush.Updated on 2026-10-22
- PDF ka size kaise kam kare, 100 KB ya 200 KB takEk scanned PDF ko 100 KB, 200 KB ya 500 KB tak kaise laaye, bina quality kharab kiye aur bina file upload kiye. Har form portal ki limit alag hoti hai.Updated on 2026-10-22
- What a file gives away when you send itPhotos carry GPS, PDFs carry the text under the black box, Office files carry the author and the hidden rows. What to check before you attach anything.Updated on 2026-10-22
- How to convert AVIF to PNG, and why the PNG comes out biggerTurn an AVIF into a PNG that any program opens, transparency kept, 20 files at once. Why the PNG is larger, and when JPG or WebP is the better target.Updated on 2026-10-15
- How to create a test file of an exact size, and find where an upload limit really isMake a file of an exact byte count up to 1 GB: PDF, JPG, PNG, CSV, ZIP, TXT or BIN. Four files show if a 2 MB limit is 2,000,000 or 2,097,152 bytes.Updated on 2026-10-15
- How to fill in a PDF form that has no fields, then sign it, without printingType on the lines of a print-only PDF form, tick its boxes and sign it. A 12-point answer sits in a 5 mm band, so it fits most printed lines.Updated on 2026-10-15
- How to make a 9:16 Short from a landscape video, with blurred or black barsTurn a 16:9 video into a 1080 × 1920 Short in the browser: press 9:16 Shorts, pick blurred or black bars, trim the clips and save. Nothing is uploaded.Updated on 2026-10-15
- How to make a photo smaller in MB, down to the size a form asks forA 4 MB phone photo is 4,096 KB; a 100 KB form limit means removing 98% of it. Set the target in KB, and fewer pixels go before the quality drops.Updated on 2026-10-15
- How to put your logo on a video, in any corner, sized and kept for next timeAdd a PNG logo to a video in the browser: it lands bottom right at 12% of the short side, moves to any corner or anywhere by dragging, and is remembered.Updated on 2026-10-15
- How to turn phone photos into one PDF, and make it small enough to uploadPut phone photos into one PDF in the order you choose, one or several per page, then shrink it for a portal. 12 photos at two per page make 6 pages.Updated on 2026-10-15
- How to reduce a PDF to 100 KB or 200 KB for a government portal, and keep it readableWhy a scan is 4 MB, how many KB each page gets under a 100 KB or 200 KB limit, the scan settings that prevent it, and what to do when it won't fit.Updated on 2026-10-05
- How to open and convert iPhone HEIC photos to JPG on WindowsWhy iPhone photos are HEIC, the two Microsoft Store extensions that let Windows open them, how to convert to JPG, and the iPhone setting that stops HEIC.Updated on 2026-10-05
- How to open a password-protected Form 16 or AIS PDF, and save a copy without the passwordWho sets the Form 16 password and where its format is written, the AIS password format, and how to save an unlocked copy for your ITR or loan file.Updated on 2026-10-05
- How to download Facebook videos and reels, the ways Facebook allowsFacebook lets you download your own reels and videos and save anyone's to watch later. Since September 2025 every new video is a reel. The steps for each.Updated on 2026-10-01
- How to download Instagram reels and posts, yours and other people'sInstagram's own Download button for public reels, saving to collections, and exporting every photo and video you posted. What each one gives you.Updated on 2026-10-01
- How to download videos from X (Twitter), the ways X allowsX Premium members can download videos whose uploader allows it, anyone can bookmark a post, and your own videos come back in your X archive.Updated on 2026-10-01
- How to download YouTube videos to watch offline, the ways YouTube allowsYouTube's own Download button works free in India for many videos, Premium unlocks the rest, and your own uploads come out of YouTube Studio as MP4.Updated on 2026-10-01
- How to turn a video you own into MP3, from YouTube, Instagram, Facebook or your phoneGet the video through the platform's own download or export, then take the sound out in your browser. What YouTube forbids, and why you get .m4a.Updated on 2026-10-01
For the money calculators
All money calculators- How to calculate GST inclusive and exclusive, and take GST out of a priceThe two GST formulas, adding GST and removing it from an inclusive price, worked at 5%, 18% and 40%, the CGST/SGST split, and why subtracting 18% is wrong.Updated on 2026-10-24
- Monthly interest on an FD, or cumulative? How each pays, with the arithmetic and TDSA non-cumulative FD pays interest monthly or quarterly; a cumulative one adds it on. ₹5 lakh at 7% for 5 years: ₹1,73,985 monthly, ₹2,07,389 cumulative.Updated on 2026-10-23
- Home loan prepayment: part payment vs full foreclosure, charges and the bank processPart payment or full foreclosure? The RBI rules on prepayment charges, the documents, the 4-step bank process and a ₹40 lakh worked example.Updated on 2026-10-23
- How to calculate HRA exemption, the least-of-three rule worked throughExempt HRA is the least of HRA received, rent minus 10% of salary, and 50% or 40% of salary. ₹50,000 basic and ₹18,000 rent: ₹13,000 a month tax-free.Updated on 2026-10-23
- Materials for one room, in the order a site buys themOne 12 by 10 foot room carried through bricks, mortar, cement, tiles and paint, with the conversions Indian suppliers sell in and where estimates slip.Updated on 2026-10-22
- What you are owed when you leave a job in IndiaNotice pay, unused leave, gratuity, provident fund and the tax on all of it, in the order they are worked out and settled after you resign.Updated on 2026-10-22
- How much interest you get on PF, and how EPFO works it out each monthPF earns 8.25% a year, worked out monthly and credited once a year. On ₹30,000 basic, the first year earns ₹2,322; ₹5 lakh already in earns ₹41,250 more.Updated on 2026-10-18
- Profit per order on Amazon, Flipkart and Meesho, after fees, GST, TCS and returnsHow to work out the profit on one marketplace order in India: GST out of the price, then fees, returns and ads. A ₹999 order worked through to ₹199.56.Updated on 2026-10-15
- Average share price after buying more, and what averaging down really changesYour average share price is total money divided by total shares, not the prices added and halved. Worked examples, the averaging-down formula, its limits.Updated on 2026-10-15
- How to count cash by denomination, and split an amount into the fewest notesCount notes and coins by denomination, with the total in figures and words: a drawer of 91 pieces worked to ₹9,587, and the fewest notes for any sum.Updated on 2026-10-15
- Income tax in France or Germany on a salary offer, worked out for someone moving from India€60,000 gross leaves €41,149 a year in France and €37,551 in Germany in 2026, single, no children. Where it goes, and what residence and the DTAA decide.Updated on 2026-10-15
- How to read a vehicle number plate in India: state, RTO, series and numberWhat each part of an Indian registration number means: MH 12 AB 1234 is Maharashtra, Pune RTO, series AB, number 1234. Delhi and BH plates too.Updated on 2026-10-15
- How EMI is calculated, the formula in plain words, with a worked exampleThe EMI formula banks use, each part explained, a ₹25 lakh home loan worked through, why early EMIs are mostly interest, and what rate and tenure do.Updated on 2026-10-05
- 75% attendance - how many classes can I miss, and how many must I attend to recover?The attendance formulas, worked: how many classes you can still miss at 75%, how many you must attend to get back to 75%, and what CBSE and colleges apply.Updated on 2026-10-05
- How to make a rent receipt for an HRA claim, and what payroll checksWhat an HRA rent receipt must show, when the landlord's PAN is needed (rent over ₹1 lakh a year), the revenue stamp myth, and the 8 cities at 50%.Updated on 2026-10-05