Hopi
Over 200 free UK-focused calculators, converters and generators as MCP tools: take-home pay and National Insurance for 2026/27, VAT, stamp duty, mortgages…
Community: Submitted by a user or imported; check the owner before granting accessOnlineNo sign-inGlobalFreeCan modify data
What it can do
- Hopi Add Working Days: 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
- Hopi Age Calculator: 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 liv
- Hopi Alcohol Unit Calculator: 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 wee
What data it sees
Do you need an account
No: the server works without sign-in
Over 200 free UK-focused calculators, converters and generators as MCP tools: take-home pay and National Insurance for 2026/27, VAT, stamp duty, mortgages, loans, savings, inflation since 1988, currency with live rates, dates and working days with bank holidays, unit conversions, health calculators, colour and text utilities, encoding, hashing, JWT and TOTP, and validators for IBANs and Bitcoin and Ethereum addresses. Every tool is read-only, stateless and computes on the spot; nothing you send is stored. Each result links to its source page on hopi.co.uk.
How to connect
How to connect Hopi to Claude
The server address to paste into Claude settings:
https://hopi--hopi.run.tools
- Open Claude (claude.ai or the desktop app).
- Go to Settings → Connectors.
- Click Add custom connector.
- Paste the server address copied below into Remote MCP server URL and click Add.
- In a chat, click + → Connectors and switch the new connector on.
Custom connectors are available on Free, Pro, Max, Team and Enterprise plans (Free is limited to one). On Team and Enterprise an organization Owner adds the connector first under Organization settings → Connectors.
Authorization
After you click Add, a sign-in window for the service opens. Sign in with your own account and approve access. Claude never sees your password.
How to connect Hopi to ChatGPT
The server address to paste into ChatGPT settings:
https://hopi--hopi.run.tools
- Open ChatGPT in a browser (chatgpt.com). A Plus, Pro, Business, Enterprise or Edu plan is required.
- Turn on developer mode once: Settings → Apps → Advanced settings → Developer mode.
- Open Settings → Connectors and click Create.
- Fill in the form: Name (anything), Description (one line about what the service does), MCP server URL (copy it below).
- Under Authentication choose OAuth if the service requires sign-in, otherwise None. Click Create.
- In a new chat open + → Apps/Connectors and enable the connector.
OpenAI has renamed this section before (Connectors → Apps/Plugins). If the label differs, search settings for "developer mode". On Business/Enterprise workspaces an admin must allow custom connectors first.
Authorization
On first use ChatGPT opens the service's sign-in window. Sign in and approve access.
How to connect Hopi to Cursor
The server address to paste into Cursor settings:
https://hopi--hopi.run.tools
Fastest: click Open in Cursor below and confirm the prompt.
Manually:
- In Cursor open Settings → Cursor Settings → MCP and click Add new global MCP server.
- Paste the JSON copied below into
~/.cursor/mcp.json(per project:.cursor/mcp.jsonin the repo root). - Save the file. The server appears in the MCP list; authorize it there if asked.
Authorization
If the service needs sign-in, an authorize button appears next to the server in the MCP list.
Server tool list (60)
Raw names from tools/list. Only developers need these.
| hopi_add_working_days | 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 and 2027 only, so outside those years just weekends are skipped. Source: https://hopi.co.uk/add-working-days/ |
| hopi_age_calculator | 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/ |
| hopi_alcohol_unit_calculator | 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/ |
| hopi_alphabetical_order | 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/ |
| hopi_angle_converter | 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/ |
| hopi_area_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/ |
| hopi_aspect_ratio_calculator | 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/ |
| hopi_average_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/ |
| hopi_base32_encoder | 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/ |
| hopi_base64 | 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/ |
| hopi_bill_splitter | 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/ |
| hopi_bingo_card_generator | 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/ |
| hopi_bitcoin_address_validator | 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/ |
| hopi_bmi_calculator | 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/ |
| hopi_body_fat_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/ |
| hopi_caesar_cipher | 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/ |
| hopi_cagr_calculator | 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/ |
| hopi_calories_to_kj | 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/ |
| hopi_case_converter | 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/ |
| hopi_cat_age_calculator | 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/ |
| hopi_celsius_to_fahrenheit | 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/ |
| hopi_character_counter | 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/ |
| hopi_cipher_identifier | 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/ |
| hopi_cm_to_feet | 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/ |
| hopi_cmyk_to_rgb | 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/ |
| hopi_coin_flip | 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/ |
| hopi_colour_name_finder | 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/ |
| hopi_colour_palette_generator | 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/ |
| hopi_colour_picker | 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/ |
| hopi_colour_shades_generator | 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/ |
| hopi_combination_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/ |
| hopi_compound_interest_calculator | 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/ |
| hopi_contrast_checker | 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/ |
| hopi_cron_expression_parser | 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/ |
| hopi_crypto_profit_calculator | 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/ |
| hopi_css_gradient_generator | 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/ |
| hopi_css_minifier | 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/ |
| hopi_csv_to_json | 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/ |
| hopi_cups_to_grams | 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/ |
| hopi_currency_converter | 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/ |
| hopi_data_size_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/ |
| hopi_date_calculator | 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/ |
| hopi_day_of_week_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/ |
| hopi_day_rate_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/ |
| hopi_days_between_dates | 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/ |
| hopi_days_until_christmas | 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/ |
| hopi_dca_calculator | 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/ |
| hopi_dice_roller | 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/ |
| hopi_diff_checker | 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/ |
| hopi_discount_calculator | 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/ |
| hopi_dog_age_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/ |
| hopi_download_time_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/ |
| hopi_due_date_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/ |
| hopi_dummy_data_generator | 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/ |
| hopi_email_link_generator | 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/ |
| hopi_emoji_remover | 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/ |
| hopi_energy_cost_calculator | 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/ |
| hopi_env_to_json | 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/ |
| hopi_eth_address_checksum | 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/ |
| hopi_eth_unit_converter | 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/ |