Euclid

AI models do not calculate.

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What it can do

  • Calculate: Deterministic calculator for mathematical expressions. Arithmetic, percentages, exponents, roots, trigonometry, logarithms, factorials, and any expression with a numerical answer.
  • Convert: Converts between units of measurement. Supports length, weight, volume, temperature, area, speed, time, data (bytes/bits), and 100+ other units.
  • Statistics: Descriptive and inferential statistics. Mean, median, mode, std dev, variance, percentile, z-test, t-test, chi-squared, confidence intervals, correlation, and normal distribution functions

What data it sees

Do you need an account

No: the server works without sign-in

AI models do not calculate. They predict the most probable next token. When the token is a number, it is often close, and sometimes wrong. The error compounds downstream.

Euclid is a deterministic computation service for AI agents. It provides 10 tools via a single MCP connection:

  • calculate: arithmetic, percentages, exponents, trig, logarithms
  • convert: unit conversions across 1,000+ unit pairs
  • statistics: mean, median, mode, variance, standard deviation, percentile
  • datetime: date differences, business days, age, timezone conversion
  • finance: loan payments, NPV, IRR, CAGR, compound interest
  • regex: pattern testing and extraction
  • color: hex/RGB/HSL conversion, contrast ratios, WCAG compliance
  • encode: base64, hex, URL, SHA-256, MD5, JWT decoding
  • validate: email, URL, phone, ISBN, credit card, UUID
  • geo: distance, bearing, bounding boxes, coordinate conversion

Free tier: 1,000 lifetime computations. No credit card required. Paid: $1.00 per 10,000 computations.

Same input. Same output. Guaranteed.

How to connect

How to connect Euclid to Claude

The server address to paste into Claude settings:

https://euclid.run.tools

  1. Open Claude (claude.ai or the desktop app).
  2. Go to Settings → Connectors.
  3. Click Add custom connector.
  4. Paste the server address copied below into Remote MCP server URL and click Add.
  5. 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 Euclid to ChatGPT

The server address to paste into ChatGPT settings:

https://euclid.run.tools

  1. Open ChatGPT in a browser (chatgpt.com). A Plus, Pro, Business, Enterprise or Edu plan is required.
  2. Turn on developer mode once: Settings → Apps → Advanced settings → Developer mode.
  3. Open Settings → Connectors and click Create.
  4. Fill in the form: Name (anything), Description (one line about what the service does), MCP server URL (copy it below).
  5. Under Authentication choose OAuth if the service requires sign-in, otherwise None. Click Create.
  6. 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 Euclid to Cursor

The server address to paste into Cursor settings:

https://euclid.run.tools

Fastest: click Open in Cursor below and confirm the prompt.

Manually:

  1. In Cursor open Settings → Cursor Settings → MCP and click Add new global MCP server.
  2. Paste the JSON copied below into ~/.cursor/mcp.json (per project: .cursor/mcp.json in the repo root).
  3. 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 (10)

Raw names from tools/list. Only developers need these.

calculateDeterministic calculator for mathematical expressions. Arithmetic, percentages, exponents, roots, trigonometry, logarithms, factorials, and any expression with a numerical answer.
convertConverts between units of measurement. Supports length, weight, volume, temperature, area, speed, time, data (bytes/bits), and 100+ other units.
statisticsDescriptive and inferential statistics. Mean, median, mode, std dev, variance, percentile, z-test, t-test, chi-squared, confidence intervals, correlation, and normal distribution functions.
datetimeCalendar and date arithmetic. Date differences, add/subtract time, age, business days, day of week, quarter, leap year, days in month.
encodeEncoding, decoding, hashing, and JWT inspection. Base64, hex, URL, HTML encoding/decoding. SHA-256/512, SHA-1, MD5 hashing. HMAC signatures. JWT decode.
financeFinancial calculations with arbitrary-precision decimal arithmetic. Loan payments, amortization, present/future value, NPV, IRR, CAGR, margin/markup, compound interest.
geoGeospatial calculations. Distance (Haversine/Vincenty), bearing, midpoint, destination point, bounding boxes, polygon area, point-in-polygon, coordinate conversions (DMS, UTM).
colorColor space conversions, WCAG accessibility checks, color manipulation, and palette generation. Supports hex, RGB, HSL, HSV, CMYK, Lab, OKLab, OKLCH.
regexSafe regex execution via RE2. Test, match, matchAll, replace, split, and escape operations. Linear-time guarantees, no ReDoS.
validateFormat validation for structured identifiers. Email (RFC 5322), URL (WHATWG), UUID (RFC 9562), credit card (Luhn), IPv4, IPv6, IBAN (mod-97).