Calculators MCP server
Exact arithmetic, statistics, units, dates and finance.
A safe expression calculator (no eval), descriptive statistics, unit and number-base conversion, calendar-aware date maths, loan and interest calculators, big-integer and number-theory tools, and linear regression.
Why use the hosted one: Models get arithmetic wrong; these answers are exact, including integers far beyond floating point.
Connect
claude mcp add --transport http hj-math https://mcp.hjlabs.in/mcp/math \
--header "Authorization: Bearer YOUR_API_KEY"Create an API key and put it in place of YOUR_API_KEY. Step-by-step guides: claude.ai and ChatGPT connectors, Claude Code, Cursor, VS Code, Claude Desktop, Windsurf, Zed, OpenAI Codex CLI, Gemini CLI.
All 28 tools
| Tool | What it does |
|---|---|
calculate | Evaluate an arithmetic expression exactly: + - * / % ^ (power), ! (factorial), parentheses, constants pi, e, tau, phi, and functions sqrt, cbrt, abs, round(x, places), floor, ceil, sin, cos, tan, asin, acos, atan, ata… |
statistics | Descriptive statistics for a list of numbers: count, sum, mean, median, mode, min, max, range, variance and standard deviation (sample and population), quartiles, percentiles you ask for, skewness, and outliers by the… |
unit_convert | Convert between units of length, mass, area, volume, speed, time, data size (SI and binary: KB vs KiB), pressure, energy, power, angle, frequency and temperature (C, F, K, R). Give a value, a from-unit and a to-unit; … |
number_base_convert | Convert a whole number of any size between bases 2 to 36 (binary, octal, decimal, hex and more). Accepts 0x, 0b, 0o prefixes and negative numbers. |
percentage | Percentage questions: "what is X% of Y", "X is what percent of Y", "percent change from X to Y", "Y increased/decreased by X%", and "what number is Y after an X% change". |
loan_emi | Monthly payment (EMI) for a loan or mortgage from principal, annual interest rate and term, with total interest, total paid and an optional year-by-year amortisation summary. |
compound_interest | Future value of a lump sum and/or regular contributions with compound interest, plus total contributions and interest earned. Compounding monthly, quarterly, yearly or daily. |
simple_interest | Simple (non-compounding) interest: interest amount and total from principal, annual rate and time in years. |
date_diff | The time between two dates: years, months and days (calendar-aware), plus total days, weeks, hours, and the weekdays between them. |
add_to_date | Add or subtract days, weeks, months or years to a date (calendar-aware: Jan 31 + 1 month = Feb 28/29). Negative amounts subtract. Returns the date and its weekday. |
day_of_week | The weekday of any date, with its day of year, ISO week number, days left in the year and whether the year is a leap year. |
working_days | Count working days (Monday to Friday) between two dates, skipping any holidays you list, or find the date a number of working days after a start date. |
age | Exact age (years, months, days) on a given date from a date of birth, plus total days lived, the next birthday and the weekday of birth. |
big_arithmetic | Exact arithmetic on whole numbers of any size: add, subtract, multiply, divide (quotient and remainder), power and modular power. Use when numbers exceed 2^53 and floating point would round. |
prime_factors | Prime factorisation of a whole number (up to about 10^24 for numbers with small factors), with the factors grouped as powers, the divisor count and the sum of divisors. |
is_prime | Test whether a whole number is prime (deterministic up to 3×10^24, Miller-Rabin beyond), and give the next and previous primes for numbers under 10^15. |
gcd_lcm | Greatest common divisor and least common multiple of two or more whole numbers (any size), and whether they are coprime. |
fraction | Simplify a fraction, convert a decimal to the closest fraction (with a maximum denominator), or convert a fraction to a decimal and a mixed number. Also adds, subtracts, multiplies and divides two fractions exactly. |
combinatorics | Exact factorial, combinations nCr, permutations nPr, and combinations with repetition, for n up to 5000 (BigInt, no rounding). |
quadratic_solver | Solve ax² + bx + c = 0: real or complex roots, the discriminant and the vertex. Also handles the linear case a = 0. |
triangle | Solve a triangle from three sides (SSS), two sides and the included angle (SAS), or two angles and a side (ASA/AAS): all sides, all angles (degrees), area, perimeter, and type. |
bmi | Body mass index from weight and height (metric or imperial), with the WHO category and the healthy weight range for that height. |
tip_split | Tip and bill splitting: tip amount, total, and the per-person share for a bill, tip percentage and number of people. Optionally round each share up to the nearest whole unit. |
format_number | Format a number for people: thousands separators in a locale, fixed decimals, currency, percent, compact ("1.2M"), scientific, or as an ordinal (1st, 2nd). |
random_number | Cryptographically random integers in a range, with or without repeats; or shuffle a list; or roll dice ("3d6"). Use when you need genuine randomness rather than a made-up number. |
sequence | Generate a numeric sequence: arithmetic (start, step, count), geometric (start, ratio, count), Fibonacci, primes, squares, cubes, triangular, or powers of two, with the sum. |
linear_regression | Fit a straight line y = m·x + b to paired data: slope, intercept, r, r² and predictions for x values you give. Use for trends and simple forecasts. |
time_duration | Convert between a duration in seconds (or ms, minutes, hours, days) and a human form like "2d 3h 4m 5s", or add up a list of durations ("1h30m", "45m", "2:15:00"). |
Try asking
What is the EMI on a 25 lakh loan at 8.5% over 20 years, and how many working days until 2026-03-31?
Usage and limits
Every account gets a free daily allowance of tool calls; connecting, listing and searching are not counted. See the limits. Only a tool that runs costs a call.