uk.co.hopi/hopi

Add or subtract a number of working days (Monday to Friday) from a start date, optionally skipping England and Wales bank holidays. Dates use the YYYY-MM-DD format. Bank holiday data covers 2026 to 2028 only, so outside those years just weekends are skipped. Source: https://hopi.co.uk/add-working-days/

Work out an exact age from a date of birth, as of today or an optional 'as of' date. Dates use the YYYY-MM-DD format. Returns the age in years, months and days, the total days lived, and the next birthday. Source: https://hopi.co.uk/age-calculator/

Build a well-structured prompt to paste into an AI chatbot or image generator. Give the task plus any of: the role the AI should take, background, audience, tone, format, length, things to avoid, an example of good output, and material to work on (for summarise, analyse and code tasks). taskType image switches to style, lighting, composition and aspect ratio instead. target formats the prompt for 'chatgpt' (Markdown headings, the task repeated after long material, as OpenAI's guidance suggests), 'claude' (XML tags with long material first and the task last, as Anthropic recommends), 'gemini' (Markdown with the question after the context, as Google recommends) or 'any'. Returns the prompt, a checklist of which parts are present, vague words found, and the word count with a rough token estimate (characters divided by 4). Nothing is sent to any AI. Source: https://hopi.co.uk/ai-prompt-builder/

Work out UK alcohol units in a drink from its ABV (percentage) and volume (millilitres), using units = ABV x ml / 1000. Optionally give the number of those drinks per week to get a weekly total compared against the NHS low risk guideline of 14 units a week. Source: https://hopi.co.uk/alcohol-unit-calculator/

Sort the lines of a block of text into alphabetical order. Blank lines are dropped. Uses natural en-GB ordering so numbers within lines sort sensibly. Can sort ascending (A to Z) or descending (Z to A), and can ignore case. Source: https://hopi.co.uk/alphabetical-order/

Convert an angle from one unit to another. Units: deg (degrees), rad (radians), grad (gradians), turn (full turns). Source: https://hopi.co.uk/angle-converter/

Convert an area from one unit to another. Units: sqm (square metres), sqft (square feet), sqyd (square yards), acre (acres), ha (hectares), sqkm (square kilometres), sqmi (square miles). Source: https://hopi.co.uk/area-converter/

Aspect ratio helper. In 'simplify' mode, give width and height to get the simplified W:H ratio, decimal ratio and nearest common ratio. In 'solve' mode, give a ratio (ratioW:ratioH) plus one of width or height to get the missing side. Source: https://hopi.co.uk/aspect-ratio-calculator/

Work out the mean, median, mode, sum, count, minimum and maximum of a list of numbers. Provide the numbers separated by spaces, commas, semicolons or new lines (type 1200 rather than 1,200, as commas are treated as separators). Source: https://hopi.co.uk/average-calculator/

Encode text to RFC 4648 Base32 or decode Base32 back to text. Encoding maps the UTF-8 bytes of the text into 5-bit groups using the alphabet A to Z then 2 to 7, padded to a multiple of 8 characters with equals signs. Decoding tolerates lowercase input and missing padding, and reports characters outside the alphabet as an error. Source: https://hopi.co.uk/base32-encoder/

Encode text to Base64, or decode a Base64 string back to text. UTF-8 safe, so accents and emoji survive the round trip. Returns the converted text or a clear error. Source: https://hopi.co.uk/base64/

Split a restaurant bill between people. In 'itemised' mode, list each item with its amount and who shared it, then add an optional tip and service charge (both percentages applied to each person's own share). In 'even' mode, split one total evenly with an optional tip. Amounts in GBP. Source: https://hopi.co.uk/bill-splitter/

Generate one or more UK 90-ball bingo cards. Each card is a 3-row by 9-column grid holding 15 numbers, 5 per row, with each column drawing from its own decade (1 to 9, 10 to 19, and so on up to 80 to 90). Blank squares are null. Source: https://hopi.co.uk/bingo-card-generator/

Build Ramanujan's birthday magic square: a 4 x 4 grid whose top row is a date (day, month, first two digits of the year, last two digits) and whose rows, columns, diagonals and many other groups of four all add up to the same total. Pass date as YYYY-MM-DD (order dmy for day first, the UK way, or mdy for month first), or pass numbers as any four whole numbers instead. With neither, it uses today's local date. Returns the square, the magic total and every group of four cells that adds up to it, with cells as [row, column] counted from 1 at the top left. builtIn is true for the 44 groups that always work and false for lucky coincidences. hasNegative and hasRepeats flag squares that use negative or repeated numbers. Source: https://hopi.co.uk/birthday-magic-square/

Check whether a Bitcoin address is valid by verifying its checksum and structure. Supports legacy Base58Check (P2PKH, P2SH) and Bech32/Bech32m SegWit and Taproot addresses, on mainnet and testnet. Does not query the blockchain or check balances. Source: https://hopi.co.uk/bitcoin-address-validator/

Work out body mass index (BMI) from height and weight, with the NHS weight category. Use units 'metric' with heightCm and weightKg, or 'imperial' with heightInches and weightPounds. BMI = weight in kg / (height in metres squared). Source: https://hopi.co.uk/bmi-calculator/

Estimate body fat percentage using the US Navy tape method from a few measurements. For males give height, neck and waist; for females give height, neck, waist and hip. Use units 'metric' (centimetres) or 'imperial' (inches). Optionally give weight (kg for metric, pounds for imperial) to also get fat mass and lean mass in kilograms. Source: https://hopi.co.uk/body-fat-calculator/

Encode or decode text with a Caesar shift cipher. Each letter is moved along the alphabet by the shift amount; a shift of 13 is ROT13. Only A to Z letters are changed, everything else is left as is. Decoding applies the opposite shift. Source: https://hopi.co.uk/caesar-cipher/

Work out the compound annual growth rate (CAGR) that takes a starting value to an ending value over a number of years. Returns the annual rate, the total growth and the growth multiple. Source: https://hopi.co.uk/cagr-calculator/

Convert food energy between kilocalories (kcal) and kilojoules (kJ) using the exact factor 1 kcal = 4.184 kJ. Give an amount and its unit ('kcal' or 'kj'); returns both values. Source: https://hopi.co.uk/calories-to-kj/

Generate the embed code for a CAPTCHA on a web form plus the server code that checks the token. Providers: turnstile (Cloudflare Turnstile), hcaptcha, recaptcha2 (reCAPTCHA v2 checkbox), recaptcha3 (reCAPTCHA v3 score) and altcha (self-hosted proof of work, no account). Servers: php, node (Express), python (Flask), cloudflare (Pages Function), netlify (Netlify Function) and vercel (Vercel Function), plus two form services that check the token themselves, so no server code is returned: netlify-forms (reCAPTCHA v2 only; with no site key Netlify supplies its own reCAPTCHA) and formspree (not altcha). ALTCHA server code is given for node and python only. The secret key is never asked for: the server code reads it from an environment variable. Set useTestKey to use the provider's official always-pass test site key (not available for recaptcha3 or altcha). Source: https://hopi.co.uk/captcha-embed-code-generator/

Convert text to a different letter case. 'upper' is UPPERCASE, 'lower' is lowercase, 'title' capitalises the first letter of each word, and 'sentence' capitalises the first letter of each sentence. Source: https://hopi.co.uk/case-converter/

Convert a cat's age in years to an approximate human age, using the standard 15, 24, then 4 a year chart. Returns the human-equivalent age and the cat's life stage. Source: https://hopi.co.uk/cat-age-calculator/

Convert a temperature between Celsius and Fahrenheit. Also returns Kelvin. Set direction to 'c-to-f' or 'f-to-c'. Source: https://hopi.co.uk/celsius-to-fahrenheit/

Count the characters in a block of text, including a count with spaces removed, the word count, how many SMS messages it would take to send, and the Twitter/X characters remaining out of 280. Source: https://hopi.co.uk/character-counter/

Identify what encoding or classical cipher a piece of text probably is (Base64, Base32, hex, binary, octal or decimal ASCII, URL encoding, HTML entities, Morse, Caesar or ROT-N, Atbash, reversed text) or recognise it as a UUID, IPv4 address, Unix timestamp, JWT or hash digest. Returns ranked candidates with confidence and a decoded preview, then auto-decodes nested layers (up to 8) while a step is at least 60% confident. Cannot break keyed encryption such as AES. Source: https://hopi.co.uk/cipher-identifier/

Convert a height between centimetres and feet/inches. Direction 'cm-to-feet' takes cm and returns feet and inches. Direction 'feet-to-cm' takes feet and inches and returns cm. Source: https://hopi.co.uk/cm-to-feet/

Convert print CMYK values (each 0 to 100) to on-screen RGB and hex, or convert RGB (each 0 to 255) the other way to CMYK. Uses the standard device-independent conversion. Source: https://hopi.co.uk/cmyk-to-rgb/

Flip a fair coin one or more times. Returns each result plus a tally of heads and tails. Source: https://hopi.co.uk/coin-flip/

Run the Collatz (3n + 1) rule on a positive whole number of up to 1,000 digits: halve it when even, treble it and add 1 when odd, until it reaches 1. Returns the total steps, odd and even step counts, the highest value reached and the step it was reached at, and the path itself (first 1,000 values; pathTruncated says whether it was cut). Exact for any size: n, peak and the path values are decimal strings. Pass big numbers as a digit string, because JSON numbers above 9,007,199,254,740,991 lose precision. Source: https://hopi.co.uk/collatz-conjecture-calculator/

Find the named CSS colour that exactly or most closely matches a hex code, using straight-line distance in RGB space across the 148 named CSS colours. Source: https://hopi.co.uk/colour-name-finder/

Generate a five-swatch colour palette from a base hex colour using a chosen scheme: analogous, complementary, triadic or mixed. Supporting swatches carry a small random variation, so results vary slightly each call. Source: https://hopi.co.uk/colour-palette-generator/

Given a six-digit hex colour code (with or without a leading #), return its hex, RGB and HSL values. Source: https://hopi.co.uk/colour-picker/

From a base hex colour, generate five progressively lighter tints (mixed towards white) and five progressively darker shades (mixed towards black), each in five equal steps of one sixth. Source: https://hopi.co.uk/colour-shades-generator/

List every way to choose r items from a list, ignoring order (combinations). Returns the total count and the combinations themselves (the first 5000). Source: https://hopi.co.uk/combination-generator/

Project savings growth from a starting deposit plus a regular monthly contribution, compounded monthly with contributions added at the end of each month. Returns the final balance, total paid in and interest earned. Amounts in GBP, rate is the annual rate as a percentage. Source: https://hopi.co.uk/compound-interest-calculator/

Work out the WCAG contrast ratio between a foreground (text) colour and a background colour, both as hex codes, and report whether it passes AA and AAA for normal and large text. Source: https://hopi.co.uk/contrast-checker/

Translate a standard five-field cron expression (minute, hour, day-of-month, month, day-of-week) into plain English. Understands stars, steps, ranges, lists and month and day names, plus shortcuts like @daily and @hourly. Source: https://hopi.co.uk/cron-expression-parser/

Work out profit or loss on a crypto trade from buy price, quantity and an optional per-side fee percentage. Returns breakeven price always, and profit, return percentage and total fees once a sell price is given. All figures are treated as GBP. Source: https://hopi.co.uk/crypto-profit-calculator/

Build a ready-to-use CSS gradient from two colours. Choose a linear gradient with an angle in degrees, or a radial gradient. Returns the gradient value and a full background declaration. Source: https://hopi.co.uk/css-gradient-generator/

Minify CSS by removing comments and needless whitespace, while preserving quoted strings and the spaces inside calc() expressions. Returns the minified CSS with before and after byte sizes. Source: https://hopi.co.uk/css-minifier/

Convert CSV text into a JSON array, following standard CSV quoting rules for embedded commas, quotes and line breaks. With headers on, the first row becomes object keys; with headers off, each row is an array of strings. Source: https://hopi.co.uk/csv-to-json/

Convert US cups of a common baking ingredient to grams (approximate). Ingredients: flour (plain flour), caster (caster sugar), brown (packed brown sugar), butter, cocoa (cocoa powder), oats, rice (uncooked rice), icing (icing sugar). Source: https://hopi.co.uk/cups-to-grams/

Convert an amount of money from one currency to another using Hopi's live mid-market exchange rates (updated hourly, 150+ currencies). Use ISO 4217 codes such as GBP, EUR, USD, JPY. Source: https://hopi.co.uk/currency-converter/

Convert a digital storage size between units. Units: B (bytes), KB, MB, GB, TB. By default 1 KB = 1000 bytes (decimal, as storage is sold). Set binary to true for 1 KB = 1024 bytes (as Windows reports drive sizes). Source: https://hopi.co.uk/data-size-converter/

Add or subtract a number of days, weeks, months or years from a date. Dates use the YYYY-MM-DD format. Months and years are clamped to the last day of the target month where needed. Returns the resulting date. Source: https://hopi.co.uk/date-calculator/

Find which day of the week a given date falls on. Dates use the YYYY-MM-DD format. Also reports which weekday that same day and month falls on in the current year. Source: https://hopi.co.uk/day-of-week-calculator/

Convert between a contractor day rate and an annual salary equivalent using a chosen number of billable working days per year (default 220). Mode 'to_salary' turns a day rate into yearly, monthly and weekly figures; mode 'to_rate' turns a salary into a day rate. Gross amounts in GBP, before tax. Source: https://hopi.co.uk/day-rate-calculator/

Count the number of days between two dates, with the total also shown in weeks and in weekdays (Monday to Friday). Dates use the YYYY-MM-DD format. Set inclusive to true to count both end days. Source: https://hopi.co.uk/days-between-dates/

Count the number of sleeps until the next Christmas Day (25 December). Uses today's date by default, or an optional 'from' date in YYYY-MM-DD format. Source: https://hopi.co.uk/days-until-christmas/

Work out the average cost basis across a series of pound-cost-averaged buys. Each buy is an amount of money spent and the price paid per unit. Returns total invested, coins acquired and average cost, plus current value and unrealised profit or loss if a current price is given. Figures are treated as GBP. Source: https://hopi.co.uk/dca-calculator/

Roll one or more dice with a given number of sides. Returns each die result plus the total, highest and lowest. Source: https://hopi.co.uk/dice-roller/

Compare two texts line by line using a longest common subsequence diff, and report which lines were added and which were removed. An edited line shows as one removed line plus one added line. Comparison is exact, including spaces and case. Source: https://hopi.co.uk/diff-checker/

Work out a discount and sale price. Mode 'pct': a percentage off a price. Mode 'fixed': a fixed pound amount off a price. Mode 'find': the discount percentage from an original price and a final price. All money figures are in pounds. Source: https://hopi.co.uk/discount-calculator/

Convert a dog's age in years to an approximate human age, using the standard veterinary chart. The later rate depends on the dog's size: small, medium or large. Returns the human-equivalent age. Source: https://hopi.co.uk/dog-age-calculator/

Estimate how long a download takes. Give a file size with its unit (MB, GB, TB) and a connection speed with its unit (Mbps or Gbps in bits per second, or MBps in bytes per second). Returns a human-readable duration and the time in seconds. Source: https://hopi.co.uk/download-time-calculator/

Estimate a pregnancy due date from the first day of the last menstrual period (LMP) and cycle length. Method: adjust the LMP by (cycle - 28) days, then add 280 days for the due date. Also returns the dates the second and third trimesters begin (LMP-adjusted + 84 and + 182 days). Dates are ISO 'YYYY-MM-DD'. Source: https://hopi.co.uk/due-date-calculator/

Generate fake but safe UK test records. Phone numbers come from Ofcom's reserved drama ranges and emails use RFC 2606 example domains, so no record can reach a real person. Returns an array of records, plus CSV text. Source: https://hopi.co.uk/dummy-data-generator/

Analyse raw email headers (the full source from Show original or View message source) without any network call: lists every Received hop in delivery order with host, IP, time and delay between hops; extracts From, Reply-To, Return-Path, Subject, Date, Message-ID and mailer; reads SPF, DKIM and DMARC results from Authentication-Results, ARC-Authentication-Results and Received-SPF with the domain each was checked for; and flags warning signs such as Reply-To on a different domain, SPF or DMARC failure, no DKIM, a display name that pretends to be an address or brand, a first hop from a home connection, clock skew and a mismatched Message-ID domain. Returns a verdict (consistent, caution or suspicious). It does not query DNS, so it reports what the receiving servers recorded rather than re-checking it. Source: https://hopi.co.uk/email-header-analyser/

Build a correctly percent-encoded mailto link from to, cc, bcc, subject and body fields, plus a ready to paste HTML anchor snippet. Spaces are encoded as %20 and line breaks as %0D%0A, as the mailto standard expects. Source: https://hopi.co.uk/email-link-generator/

Remove emoji from a block of text, leaving the words and normal punctuation intact. Joined emoji sequences (such as a family or a flag) count as a single emoji. The copyright, registered and trademark symbols are kept. Returns the cleaned text and how many emoji were removed. Source: https://hopi.co.uk/emoji-remover/

Work out the running cost of an electrical appliance from its power in watts, hours used per day and your electricity unit price in pence per kWh. Returns daily, weekly, monthly and yearly cost plus kWh used. Costs in GBP. Source: https://hopi.co.uk/energy-cost-calculator/

Convert between a .env file and a JSON object. In env-to-json mode, each line is split on its first equals sign into a key and value, blank and commented lines are skipped, a leading export is removed, and matching surrounding quotes are stripped (double-quoted values also unescape \n); duplicate keys keep the last value. In json-to-env mode, a JSON object becomes KEY=value lines, quoting values that contain spaces, a hash or a newline. Source: https://hopi.co.uk/env-to-json/

Validate an Ethereum address's EIP-55 capitalisation checksum and return the correctly checksummed form. Reports whether the input is already checksummed, lacks a checksum (all one case), or fails the checksum. Uses keccak-256 exactly as EIP-55 specifies. Source: https://hopi.co.uk/eth-address-checksum/

Convert an amount given in wei, gwei or ETH into all three units, using exact 18-decimal integer maths (no floating point error). 1 ETH is 1e18 wei; 1 gwei is 1e9 wei. Source: https://hopi.co.uk/eth-unit-converter/

Generate random EuroMillions lines. Each line has 5 main numbers from 1 to 50 and 2 Lucky Stars from 1 to 12. Source: https://hopi.co.uk/euromillions-generator/

Work out how many bottles of red, white and Champagne to buy for an event, from the number of guests and glasses per guest. Ticking different wines splits a colour into one wine per glass, each poured once for every guest. Source: https://hopi.co.uk/event-wine-calculator/

Crack open a virtual fortune cookie and receive a random cheerful fortune. Returns the fortune. Source: https://hopi.co.uk/fortune-cookie/

Add, subtract, multiply or divide two fractions, giving the simplified result, a mixed number where relevant, and the decimal value. Each fraction is a numerator over a denominator, all whole numbers (numerators may be negative). Source: https://hopi.co.uk/fraction-calculator/

Convert between fractions and decimals. Mode 'toDecimal': give a numerator and denominator (whole numbers) to get the decimal and percentage. Mode 'toFraction': give a decimal to get the closest simplified fraction (denominator up to 10,000), noting whether it is exact. Source: https://hopi.co.uk/fraction-to-decimal/

Estimate the fuel cost of a journey from the distance in miles, the car's fuel economy in miles per gallon (UK gallon) and the pump price in pence per litre. Optionally double it for a return trip and split between passengers. Returns total cost, litres used and cost per person. Costs in GBP. Source: https://hopi.co.uk/fuel-cost-calculator/

Compute the SHA-256, SHA-1 or SHA-512 hash of a piece of text and return the hex digest. Uses WebCrypto on Hopi's server. SHA-1 is included for compatibility with older systems only and should not be used for anything new. Source: https://hopi.co.uk/hash-generator/

Identify the most likely algorithms behind a hash string from its length, character set and any prefix. Covers MD5, NTLM, MD4, SHA-1, RIPEMD-160, SHA-224/256/384/512, the SHA3 family, CRC32, bcrypt, Argon2, sha512crypt, sha256crypt and md5crypt, plus Base64 length hints. A hash does not carry its algorithm, so results are ranked best guesses, not proof. Source: https://hopi.co.uk/hash-identifier/

Estimate maximum heart rate and five training zones (bpm) from age. Max HR = 220 - age. Method 'max' uses percentages of max HR (50-60, 60-70, 70-80, 80-90, 90-100%). Method 'karvonen' uses heart rate reserve and needs restingHeartRate: zone = (maxHR - resting) x intensity + resting. Source: https://hopi.co.uk/heart-rate-zones/

Convert a hex colour code (3, 6 or 8 digits, with or without a leading #) to its RGB and HSL values. Source: https://hopi.co.uk/hex-to-rgb/

Scan text for hidden and suspicious Unicode characters and return a cleaned copy. Finds zero-width space, joiner and non-joiner (U+200B to U+200D), word joiner U+2060, byte order mark U+FEFF, soft hyphen U+00AD, no-break and narrow no-break spaces, hair and thin spaces, bidirectional controls (U+202A to U+202E, U+2066 to U+2069), variation selectors, Unicode tag characters U+E0000 to U+E007F (the invisible prompt-injection carrier, decoded to readable text in tagText), control characters, every other default-ignorable or format character (for example the Khmer inherent vowels U+17B4 and U+17B5 used to pad AI text), and Latin words containing Cyrillic or Greek lookalike letters. Curly quotes and dashes are reported separately as stylistic, not hidden. The cleaned text removes the invisible characters, turns special spaces into ordinary spaces and keeps zero-width joiners and selectors that form emoji. It cannot detect statistical AI watermarks such as SynthID-Text, which live in word choice. Source: https://hopi.co.uk/hidden-character-checker/

Work out UK statutory paid holiday entitlement from the number of days worked per week, using 5.6 weeks a year capped at the statutory 28 days. Optionally scale to a part-year by the number of months worked. Returns entitlement in days and weeks. Source: https://hopi.co.uk/holiday-entitlement-calculator/

Generate a honeypot spam trap for a web form: the hidden field HTML, the CSS that moves it off-screen, and the server check that quietly rejects submissions where it is filled. Platforms: php, node (Express), python (Flask), cloudflare (Pages Function), netlify (Netlify Forms netlify-honeypot attribute) and formspree (its fixed _gotcha field). An optional time trap rejects forms sent faster than minSeconds; it needs JavaScript and does not apply to netlify or formspree. Warns when the field name is one browsers might autofill. Source: https://hopi.co.uk/honeypot-field-generator/

Convert between an hourly pay rate and an annual salary based on hours worked per week (52 weeks a year). Mode 'to_salary' turns an hourly rate into annual, monthly and weekly pay; mode 'to_hourly' turns a salary into an hourly rate. Gross amounts in GBP, before tax. Source: https://hopi.co.uk/hourly-to-salary/

Work out the hours worked between a start time and an end time, minus an optional unpaid break. Times use 24-hour HH:MM format. Handles overnight shifts where the end time is earlier than the start. Returns the worked time as hours and minutes and as decimal hours. Source: https://hopi.co.uk/hours-calculator/

Convert a hex colour code to hue, saturation and lightness (HSL), or convert HSL values to hex and RGB. Source: https://hopi.co.uk/hsl-converter/

Escape the five special HTML characters (& < > " ') into entities so text is safe to place in HTML, or unescape named and numeric HTML entities back into plain characters. Source: https://hopi.co.uk/html-escape/

Look up a standard HTTP status code by number and get its name, meaning and class (1xx to 5xx), or search all standard codes by a word in the number, name or description. Source: https://hopi.co.uk/http-status-codes/

Validate an IBAN or generate a test IBAN. Pass 'iban' to check it: the tool normalises it (uppercase, no spaces), confirms the length matches the country's published length, and runs the mod-97 checksum (move the first four characters to the end, map letters to numbers A=10 to Z=35, valid when the number mod 97 is 1). Pass 'country' (a two-letter ISO code) to generate a structurally valid TEST IBAN with a random bank and account portion and correct check digits. Generated IBANs are test values only and are not tied to any real account. All processing is local; nothing is stored. Source: https://hopi.co.uk/iban-validator/

Build a .ics (iCalendar, RFC 5545) calendar file for a single event and return the file text. Give a title, startDate and endDate as 'YYYY-MM-DD'. For timed events give startTime and endTime as 'HH:MM' (24-hour, read in the caller's local time zone and stored as UTC); set allDay true for an all-day event instead. Location and description are optional. Returns the .ics text ready to save. Source: https://hopi.co.uk/ics-generator/

Adjust a money amount for UK inflation. Mode 'cpi' uses the ONS monthly CPI index (2015 = 100) between two months from January 1988 to September 2026 and returns the adjusted value, total change and average annual rate. Mode 'custom' compounds a chosen annual rate over a number of years. Amounts in GBP. Source: https://hopi.co.uk/inflation-calculator/

Estimate UK inheritance tax (IHT) on a death estate, side by side for a death before 6 April 2027 and from 6 April 2027, when unused pension funds and pension death benefits start to count towards the estate. Applies the £325,000 nil-rate band (reduced by gifts in the last 7 years), the £175,000 residence nil-rate band when the home goes to children or grandchildren (capped at the home's value, tapered £1 for every £2 the estate is over £2 million), transferred unused bands from a late spouse or civil partner (as a percentage, up to 100% extra), the spouse/civil partner and charity exemptions, and the 36% rate when at least 10% of the baseline goes to charity. Amounts in GBP. Simplified: no business or agricultural relief, no taper relief on gifts, no trusts. Not advice. Source: https://hopi.co.uk/inheritance-tax-calculator/

Work out the totals for a UK invoice or full VAT invoice from its line items, in whole pence. Each line has a quantity, a unit price before VAT and, when vatRegistered is true, a VAT rate of 20, 5, 0, exempt or outside (the scope of VAT). VAT is rounded to the nearest penny on each line and summed per rate, as HMRC VAT Notice 700 allows. Returns line, per-rate and invoice totals, the total VAT in sterling for a foreign-currency VAT invoice (needs exchangeRate), the due date from termsDays, whether a simplified VAT invoice is allowed, the late payment compensation band and a list of missing details. Totals only: the printable invoice and PDF are made on the page, and descriptions are never echoed back. Source: https://hopi.co.uk/invoice-generator/

Pretty print, minify or validate JSON. Formatting and minifying only change whitespace; key order, values and structure stay exactly as they were. Returns the output text or a clear parse error. Source: https://hopi.co.uk/json-formatter/

Convert a JSON array of objects into CSV. The union of all keys becomes the header row in first-seen order, missing keys become empty cells, and nested objects or arrays are written back as compact JSON in the cell. Output follows RFC 4180 quoting. Source: https://hopi.co.uk/json-to-csv/

Convert a JSON sample into TypeScript interfaces and types. Objects become named interfaces (PascalCase from their key), nested objects get their own interfaces, arrays become element-type arrays with keys merged across all elements (keys missing from some elements are marked optional), and null values are folded into unions such as string | null. Empty arrays become unknown[] and empty objects become Record<string, unknown>. Runs on Hopi's server; nothing is stored. Source: https://hopi.co.uk/json-to-typescript/

Convert data between JSON and YAML in both directions. JSON to YAML parses with JSON.parse and serialises with js-yaml at two-space indent; YAML to JSON parses with js-yaml and prints with JSON.stringify. Runs on Hopi's server; nothing is stored. Source: https://hopi.co.uk/json-yaml-converter/

Decode a JSON Web Token's header and payload from base64url. The signature is never verified, so a decoded claim proves nothing on its own. Reports the algorithm, the exp, iat and nbf time claims, and whether the token is expired. A leading Bearer prefix and whitespace are handled. Source: https://hopi.co.uk/jwt-decoder/

Convert a weight in kilograms to pounds (avoirdupois lb), with the answer also split into whole pounds and ounces. Uses exactly 0.45359237 kg per pound and 16 ounces per pound. Source: https://hopi.co.uk/kg-to-lbs/

Convert a weight in kilograms to UK stone and pounds. Returns whole stone plus remaining pounds, and the totals in pounds and decimal stone. Source: https://hopi.co.uk/kg-to-stone/

Convert a weight in pounds (avoirdupois lb) to kilograms and grams, with the UK stones-and-pounds form alongside. Uses exactly 0.45359237 kg per pound and 14 pounds per stone. Source: https://hopi.co.uk/lbs-to-kg/

Watermark a document per recipient and trace a leaked copy. Mode 'mark' takes text and a list of recipient names (up to 255) and returns one copy per recipient carrying that recipient's number as an 18-character invisible marker (U+2060 frame, 8-bit number plus 8-bit check written in U+200B and U+200C) after the first word and every twentieth word, plus a tracer key that stores the list; set spacing to also encode the pattern in no-break spaces. Mode 'trace' takes a leaked copy plus the same recipients or the key and returns the recipient, the copy number, how many markers were found and agreed, and a confidence level. Marks survive copy and paste but not retyping, screenshots, OCR or a hidden-character cleaner. Source: https://hopi.co.uk/leak-tracer/

Check whether a year is a leap year, applying the divisible-by-4, century, and divisible-by-400 rules. Returns the verdict, the divisibility tests, and the next and previous leap years. Source: https://hopi.co.uk/leap-year-checker/

Convert a length from one unit to another. Units: mm, cm, m, km, in (inches), ft (feet), yd (yards), mi (miles). Source: https://hopi.co.uk/length-converter/

Clean and inspect a URL without visiting it: strips tracking parameters (utm_*, fbclid, gclid, msclkid, mc_eid, _hsenc and many more, grouped by network), unwraps redirect wrappers whose destination is in the address itself (Outlook Safe Links, Proofpoint URL Defense v2 and v3, Google /url?q=, Facebook l.php, YouTube, LinkedIn, Reddit, Slack, Tumblr) and checks the address for phishing signs: punycode and mixed-script hosts, brand names in subdomains, embedded user:pass@, IP hosts, data: and javascript: schemes, risky TLDs, link shorteners, double encoding and overlong paths. Returns the clean link, what was removed, the real registrable domain, a list of warnings and a verdict (clean, caution or avoid). It cannot know where a shortener goes or whether a site is malicious; no DNS or HTTP requests are made. Source: https://hopi.co.uk/link-cleaner/