Suites · property
Property and lettings
Lettings and property: rent proration and reviews, deposit caps, service charges, yields, stamp duty, council tax, mortgage affordability and completion statements.
64 capabilities (27 core, 37 optional) and 13 gaps, in build order. Put each line in the file that calls it, then fune build.
Not legal or tax advice. Stamp duty, deposit caps and council tax follow UK nations' rules on a date; check with a solicitor or tax adviser before relying on them.
TypeScript Python Rust
1. Tenancies and rent
Set up tenancies and charge rent correctly.
property.rent-proration core Unreviewed
Rent for part of a month by the annual-daily or calendar-month method, for move-in and move-out.
Rent for part of a month from the monthly rent, by the annual-daily or the calendar-month method.
from fune.property.rent_proration import prorate_rent # property.rent-proration@^1
1.0.1
property.deposit-cap core Unreviewed
The maximum tenancy deposit (five or six weeks' rent) under the Tenant Fees Act 2019.
Maximum tenancy deposit a landlord may take: five or six weeks' rent under the Tenant Fees Act 2019.
from fune.property.deposit_cap import deposit_cap # property.deposit-cap@^1
1.0.2
property.holding-deposit-cap core Unreviewed
The maximum holding deposit to reserve a property: one week's rent.
Maximum holding deposit to reserve a rental property: one week's rent (annual rent ÷ 52), rounded down.
from fune.property.holding_deposit_cap import holding_deposit_cap # property.holding-deposit-cap@^1
1.0.1
property.rent-review optional Unreviewed
New rent after an index-linked review with collar, cap and upward-only option.
New rent after an index-linked (CPI/RPI) rent review, with an optional collar and cap and upward-only option.
from fune.property.rent_review import rent_review # property.rent-review@^1
1.0.1
dates.recurrence optional
Monthly rent due dates, month-end safe.
The next n dates of a repeating rule: monthly on a day, last weekday of the month, every k days or weeks, yearly.
from fune.dates.recurrence import recurrence # dates.recurrence@^1
1.0.0
deposit-protection Registering deposits with a protection scheme (DPS, TDS, mydeposits) is done through their services.right-to-rent Right to Rent immigration checks are a Home Office process caps does not have.
2. Service charges and blocks
Share a building's costs between its units.
property.service-charge-apportion core Unreviewed
Apportions a service charge across units by lease fraction, floor area or percentage, exact to the penny.
Apportion a service charge across units by lease fraction, floor area or fixed percentage, exact to the penny.
from fune.property.service_charge_apportion import apportion_service_charge # property.service-charge-apportion@^1
1.0.1
property.floor-area optional Unreviewed
Floor area from room dimensions in square metres and square feet.
Floor area from room lengths and widths, exactly, with the total in both square metres and square feet.
from fune.property.floor_area import floor_area # property.floor-area@^1
1.0.2
property.council-tax-band optional Unreviewed
Council tax for a band from the authority's Band D charge, England, Wales and Scotland.
Council tax for a valuation band from the Band D charge: the statutory band ratio, England, Wales and Scotland.
from fune.property.council_tax_band import council_tax_band # property.council-tax-band@^1
1.0.2
3. Buying and conveyancing
Work out what a purchase costs and what changes hands on completion.
property.stamp-duty core Unreviewed
SDLT, LBTT or LTT on a purchase, with first-time buyer relief and surcharges.
Stamp duty on a property purchase: SDLT (England, NI), LBTT (Scotland), LTT (Wales), with reliefs and surcharges.
from fune.property.stamp_duty import stamp_duty # property.stamp-duty@^1
1.0.2
property.completion-statement core Unreviewed
A buyer's completion statement: price less deposit, apportioned ground rent and service charge, fees.
A buyer's completion statement: price less deposit, ground rent and service charge apportioned to completion, plus fees.
from fune.property.completion_statement import completion_statement # property.completion-statement@^1
1.0.1
property.mortgage-affordability optional Unreviewed
Mortgage income multiple and stress-tested repayment against income.
Mortgage affordability: the loan-to-income multiple and a stress-tested repayment against income, both checked.
from fune.property.mortgage_affordability import mortgage_affordability # property.mortgage-affordability@^1
1.0.1
lending.loan-payment optional Unreviewed
Monthly mortgage payment for a principal, rate and term.
Level repayment for a loan (annuity formula), computed exactly and rounded once, the way you choose.
from fune.lending.loan_payment import loan_payment # lending.loan-payment@^1
1.0.1
lending.ltv optional Unreviewed
Loan-to-value and its band, for mortgage quotes.
Loan-to-value ratio in basis points, and the band it falls in from a band table you supply.
from fune.lending.ltv import loan_to_value # lending.ltv@^1
1.0.1
4. Investment returns
Judge a property as an investment.
property.rental-yield optional Unreviewed
Gross and net rental yield from annual rent, costs and value.
Gross and net rental yield of a let property, in basis points, from annual rent, costs and value.
from fune.property.rental_yield import rental_yield # property.rental-yield@^1
1.0.1
Hold money as currency-tagged integer minor units and do plain arithmetic on it safely.
money.amount core
The Money type ({ minor, currency }) every other money capability takes and returns.
A currency-tagged monetary amount held in integer minor units.
from fune.money.amount import money # money.amount@^1
1.0.2
money.add core
Adds and subtracts amounts, refusing to mix currencies by accident.
Add, subtract and negate monetary amounts, refusing to mix currencies.
from fune.money.add import add_money # money.add@^1
1.0.1
money.sum core
Totals a list of amounts, with an explicit currency for an empty list.
Total a list of monetary amounts, with an explicit currency for the empty case.
from fune.money.sum import sum_money # money.sum@^1
1.0.1
money.compare core
Compares, mins, maxes and clamps amounts of one currency without unwrapping them.
Compare two amounts of one currency, refusing to compare across currencies; min, max and clamp too.
from fune.money.compare import compare_money, min_money, max_money, clamp_money # money.compare@^2
2.0.04 functions
6. Rates and rounding from money-basics
Apply percentages and divide amounts with the rounding stated, never a float.
money.apply-rate core
Applies a basis-point rate (VAT, discount, commission) to an amount with explicit rounding.
Apply a rate expressed in basis points to a monetary amount, with an explicit rounding mode.
from fune.money.apply_rate import apply_rate # money.apply-rate@^1
1.0.1
math.round-div core
Integer division with a named rounding mode, for any money maths the others do not cover.
Integer division with an explicit rounding mode, for money arithmetic that must not drift.
from fune.math.round_div import round_div # math.round-div@^1
1.0.0
math.basis-points optional
Converts "12.5%" to and from basis points exactly, for rates typed in by users.
Convert a rate between percent, basis points and a plain ratio exactly, as decimal text or integer basis points.
from fune.math.basis_points import convert_rate, to_basis_points, from_basis_points # math.basis-points@^2
2.0.03 functions
math.percent-change optional
Percentage change between two figures in basis points, for "up 4.2% on last month".
Percentage change from one value to another, in basis points, with an explicit rounding mode.
from fune.math.percent_change import percent_change # math.percent-change@^1
1.0.0
math.rational optional
Exact fractions for rates that must not drift across many steps.
Exact fraction arithmetic, always reduced, for rates and ratios that must not drift.
from fune.math.rational import calculate_rational, rational, add_rational, subtract_rational, multiply_rational, divide_rational, compare_rational, rational_to_integer # math.rational@^2
2.0.08 functions
math.round-div-big optional
Rounded division on numbers past 2^53, for very large totals.
Divide two integers of any size with an explicit rounding mode, on decimal strings, for exact money sums past 2^53.
from fune.math.round_div_big import round_div_big # math.round-div-big@^1
1.0.0
Divide an amount between people, periods or lines so the parts add back to the whole.
money.allocate core
Splits an amount by ratios (60/40, by quantity) without losing or inventing a penny.
Split an amount across ratios without losing or inventing a single minor unit.
from fune.money.allocate import allocate # money.allocate@^1
1.0.1
money.split-even optional
Splits an amount into n near-equal parts that sum exactly, for instalments or shares.
Split an amount into n near-equal parts that add back up to exactly the whole.
from fune.money.split_even import split_even # money.split-even@^1
1.0.0
8. Display and input from money-basics
Show amounts to people and read what they type.
money.format core
Renders an amount as text with the currency's real number of decimal places.
Render a monetary amount as text, using the currency's real minor-unit precision.
from fune.money.format import format_money # money.format@^1
1.0.0
money.parse optional
Reads "£1,234.50" or "1.234,50 €" typed by a user into minor units, strictly.
Parse "£1,234.50" or "1.234,50 €" into integer minor units, strictly: no guessing, no rounding.
from fune.money.parse import parse_money # money.parse@^1
1.0.0
money.currency-digits optional
How many decimal places each ISO 4217 currency has, for input boxes and validation.
How many decimal places a currency's minor unit has, from the ISO 4217 list.
from fune.money.currency_digits import currency_digits # money.currency-digits@^1
1.0.0
9. Other currencies from money-basics
Convert between currencies at a rate you hold.
money.convert optional
Converts an amount at a supplied exact rate with explicit rounding.
Convert an amount to another currency at a supplied exact rate, with an explicit rounding mode.
from fune.money.convert import convert_money # money.convert@^1
1.0.0
10. Calendar arithmetic from dates-basics
Move and measure ISO dates exactly, with no date library and no clock reads.
dates.add-days core
Shifts a date by whole days, for due dates and windows.
Shift an ISO date by a whole number of days, forwards or backwards, with exact calendar arithmetic.
from fune.dates.add_days import add_days # dates.add-days@^1
1.0.0
dates.add-months core
Adds months clamping to month end, so 31 January plus a month is the end of February.
Add calendar months to an ISO date, clamping to the month end: 31 Jan + 1 month is 28 or 29 Feb.
from fune.dates.add_months import add_months # dates.add-months@^1
1.0.0
dates.days-between core
Signed calendar days between two dates, for ages of invoices and stays.
Calendar days from one ISO date to another, signed: negative when the second date is earlier.
from fune.dates.days_between import days_between # dates.days-between@^1
1.0.0
dates.month-boundaries core
First and last day of a date's month, for monthly periods and statements.
The first day, last day and length of the calendar month containing a date.
from fune.dates.month_boundaries import month_boundaries # dates.month-boundaries@^1
1.0.0
dates.day-of-week core
ISO weekday of a date, for weekend rules and opening hours.
The ISO 8601 day of the week for a date: 1 is Monday through 7 is Sunday.
from fune.dates.day_of_week import day_of_week # dates.day-of-week@^1
1.0.0
dates.is-leap-year optional
Whether a year is a leap year, for 365/366-day calculations.
Whether a year is a Gregorian leap year: every 4th, except centuries, except every 400th.
from fune.dates.is_leap_year import is_leap_year # dates.is-leap-year@^1
1.0.0
dates.overlap optional
Days two date ranges share, for prorating and clash checks.
Days two date ranges have in common, with the end of each range stated as inclusive or exclusive.
from fune.dates.overlap import overlap_days # dates.overlap@^1
1.0.0
dates.age optional
Age in whole years on a date, handling 29 February birthdays.
Age in whole years on a given date, with 29 February birthdays ageing on 1 March in other years.
from fune.dates.age import age # dates.age@^1
1.0.0
11. Periods and reporting dates from dates-basics
Put dates into the periods reports are grouped by.
dates.quarter core
Calendar and fiscal quarter of a date for any year-start month.
Calendar quarter and fiscal quarter of a date, with the fiscal year and quarter date ranges, for any start month.
from fune.dates.quarter import quarter # dates.quarter@^1
1.0.0
dates.week-number optional
ISO week number and week-year, for weekly reports.
ISO 8601 week number and week-numbering year of a date: weeks start Monday, week 1 holds the first Thursday.
from fune.dates.week_number import week_number # dates.week-number@^1
1.0.0
dates.day-count-fraction optional
Year fraction by ACT/365F, ACT/360, 30/360 or ACT/ACT, for interest periods.
Year fraction between two dates by ACT/365F, ACT/360, 30/360, 30E/360 or ACT/ACT ISDA, as an exact fraction.
from fune.dates.day_count_fraction import day_count_fraction # dates.day-count-fraction@^1
1.0.0
12. Working days and holidays from dates-basics
Skip weekends and public holidays when counting or adding days.
dates.bank-holidays core
UK bank holidays for a region and year, as gov.uk publishes them.
UK bank and public holidays for a region and year, as published by gov.uk, including one-off holidays.
from fune.dates.bank_holidays import bank_holidays # dates.bank-holidays@^1
1.0.1
dates.add-business-days core
Moves a date by working days, skipping weekends and a holiday list.
Move a date forward or back by working days, skipping weekends and a caller-supplied holiday list.
from fune.dates.add_business_days import add_business_days # dates.add-business-days@^1
1.0.0
dates.business-days-between core
Working days between two dates, for SLAs and notice periods.
Working days between two dates, excluding weekends and a caller-supplied holiday list.
from fune.dates.business_days_between import business_days_between # dates.business-days-between@^1
1.0.0
13. Times and durations from dates-basics
Work with times of day, durations and timestamps.
time.duration optional
Parses and adds durations like 1h30m in whole minutes, and formats the total.
Parse durations written as 1h30m, 90m or 01:30, add them up in whole minutes, and format the total.
from fune.time.duration import duration # time.duration@^1
1.0.0
time.minutes-between optional
Minutes between two local date-times, across midnight.
Minutes from one local date and time to another, correct across midnight; wall-clock time, no time zones.
from fune.time.minutes_between import minutes_between # time.minutes-between@^1
1.0.0
time.round-to-increment optional
Rounds minutes to a billing increment such as 6 or 15.
Round a duration in minutes to a billing increment such as 6 or 15 minutes, up, down or to nearest.
from fune.time.round_to_increment import round_to_increment # time.round-to-increment@^1
1.0.0
time.iso-to-unix optional
RFC 3339 timestamps to Unix seconds.
An RFC 3339 timestamp with a Z or offset, such as 2026-09-26T13:00:00+01:00, to Unix time in whole seconds.
from fune.time.iso_to_unix import iso_to_unix # time.iso-to-unix@^1
1.0.0
time.unix-to-iso optional
Unix seconds to an ISO 8601 UTC timestamp.
Unix time in seconds to an ISO 8601 UTC timestamp such as 2026-09-26T12:00:00Z, for years 0001 to 9999.
from fune.time.unix_to_iso import unix_to_iso # time.unix-to-iso@^1
1.0.0
time.countdown optional
Seconds left until a moment and a 4:05 style timer text.
Seconds left until a Unix time, whether it has passed, and a timer text like 4:05, for tokens or retry waits.
from fune.time.countdown import countdown # time.countdown@^1
1.0.0
Check payee and customer bank details before money moves.
validation.iban core
Checks an IBAN's mod-97 checksum and its country's length.
Check an IBAN against the ISO 13616 mod-97-10 checksum and the registered length for its country.
from fune.validation.iban import is_iban # validation.iban@^1
1.0.0
validation.bic optional
Checks a SWIFT/BIC code's format and splits it.
Check the format of a SWIFT/BIC code (8 or 11 characters) and split it into its parts.
from fune.validation.bic import validate_bic # validation.bic@^1
1.0.0
validation.uk-sort-code-account optional
Checks a UK sort code and account number by the Vocalink modulus rules, against a table you supply.
Check a UK sort code and account number with the Vocalink/Pay.UK modulus rules, against a table you supply.
from fune.validation.uk_sort_code_account import validate_uk_sort_code_account # validation.uk-sort-code-account@^3
3.0.0
validation.uk-modulus-table optional
Parses Vocalink's VALACDOS and SCSUBTAB files into that table.
Parse Vocalink's VALACDOS.txt and SCSUBTAB.txt into the table UK sort code modulus checking needs.
from fune.validation.uk_modulus_table import parse_uk_modulus_table # validation.uk-modulus-table@^1
1.0.0
16. Identifiers and check digits from validation-basics
Catch mistyped reference numbers by their check digits.
validation.luhn optional
Luhn mod-10 check, for card numbers and many reference numbers.
Check a digit string against the Luhn mod-10 checksum used by payment cards and many identifiers.
from fune.validation.luhn import is_luhn # validation.luhn@^1
1.0.0
validation.uk-company-number optional
Checks a Companies House number's format and prefix.
Check a Companies House company number's format and prefix (SC, NI, OC, LP...) and zero-pad it to eight characters.
from fune.validation.uk_company_number import validate_uk_company_number # validation.uk-company-number@^2
2.0.1
validation.lei optional
Checks a Legal Entity Identifier's check digits.
Check a 20-character Legal Entity Identifier against its ISO 17442 / ISO 7064 MOD 97-10 check digits.
from fune.validation.lei import validate_lei # validation.lei@^1
1.0.0
validation.gtin optional
Checks an EAN/UPC/GTIN barcode number.
Check an EAN-8, UPC-A, EAN-13 or GTIN-14 barcode number against the GS1 mod-10 check digit.
from fune.validation.gtin import validate_gtin # validation.gtin@^1
1.1.0
17. Displaying sensitive values from validation-basics
Show stored identifiers without exposing them.
text.mask optional
Masks all but the last digits of a card, account or phone number.
Mask all but the last n characters of a card, account or phone number, optionally keeping separators.
from fune.text.mask import mask # text.mask@^1
1.0.0
Gaps What this kind of app usually needs that Functional Weave does not have yet: write these yourself, or use a service.
property-data Property listings, valuations and portal feeds (Rightmove, Zoopla, Land Registry price paid) come from data providers.maintenance-jobs Maintenance requests, contractor jobs and inspections are workflow caps does not have.client-money Client money accounting for agents (CMP rules, client account reconciliation) is yours.fx-rate-source Where exchange rates come from: money.convert takes a rate you supply; fetching and storing daily rates (ECB, a provider's API) is yours.money-storage Storing amounts: the database columns (integer minor units plus a currency code) and their migrations are yours.time-zones Time zones and daylight saving: caps works in ISO dates, UTC and wall-clock times; converting with the IANA tz rules is yours.locale-formatting Showing dates in a user's language and format ("3 octobre 2026"): caps returns ISO dates, not localised text.non-uk-holidays Public holidays outside the UK: dates.bank-holidays is UK only; pass another country's list to the working-day functions yourself.address-lookup Turning a postcode into a list of addresses (Royal Mail PAF or a lookup API) is network work and not in caps.email-deliverability Whether a mailbox exists (MX lookups, a confirmation email): validation.email checks the syntax only.vocalink-data The Vocalink modulus tables themselves: download them from Pay.UK under its terms; caps parses them but does not ship them.