# JustOnlyOneThing > JustOnlyOneThing provides 22 free, client-side web utilities: 16 financial decision calculators and 6 developer productivity tools. All computations execute locally in the user's web browser using client-side JavaScript with zero server requests, zero tracking scripts, and zero advertising. Website: https://justonlyonething.com/ Full Technical Reference & Formulas: https://justonlyonething.com/llms-full.txt License: Free / Open Access Execution Environment: 100% Client-Side Web Browser (No backend database, no login required) Target Audience: Software developers, individual retail investors, startup founders, and financial analysts. ## What JustOnlyOneThing Does JustOnlyOneThing provides two distinct categories of single-purpose browser tools: 1. Financial Decision Calculators (16 tools): Calculates mortgage amortizations, rent versus buy equity comparisons, systematic investment plans (SIP), compounding interest, startup runway, and business valuation metrics. 2. Developer Productivity Utilities (6 tools): Formats and repairs JSON, encodes and decodes Base64 and Base64URL, tests and debugs regular expressions, verifies JWT tokens, parses cron expressions, and generates cryptographic hashes. ## Core Pages - [Homepage](https://justonlyonething.com/): Unified portal featuring all 22 tools, live country financial localization (India, US, UK, Canada, Australia, Germany, UAE, Singapore), and global fuzzy search. - [Services Hub](https://justonlyonething.com/services/): Directory of all 22 tools filterable by category (All, Finance, Developer) and keyword search. - [About](https://justonlyonething.com/about/): Architecture, developer background, privacy model, and client-side execution details. - [Blog](https://justonlyonething.com/blog/): Essays and mathematical deep dives on personal finance and software engineering. - [HTML Site Map](https://justonlyonething.com/site-map/): Complete human-readable hierarchical directory of all 22 tools, articles, author profile, and technical resources. ## Financial Decision Calculators (16 Tools) - [Rent vs Own House Calculator](https://justonlyonething.com/services/rent-vs-buy/): Compares the 20–30 year net wealth outcome of buying a home with a mortgage versus renting and investing the difference in equity mutual funds. - [SIP Wealth Calculator](https://justonlyonething.com/services/sip-calculator/): Calculates maturity corpus, total investment, and compound wealth gain for monthly Systematic Investment Plans with optional annual step-up percentage. - [Compounding Interest Calculator](https://justonlyonething.com/services/compounding-calculator/): Calculates compound interest across daily, monthly, quarterly, semi-annual, and annual frequencies with recurring monthly deposits. - [CAGR Calculator](https://justonlyonething.com/services/cagr-calculator/): Calculates the Compound Annual Growth Rate percentage between an initial investment value and a final value over a given number of years. - [SWP Retirement Calculator](https://justonlyonething.com/services/swp-calculator/): Simulates Systematic Withdrawal Plans for retirement, calculating monthly cash payouts, remaining principal, and portfolio depletion dates. - [Simple Interest Calculator](https://justonlyonething.com/services/simple-interest-calculator/): Calculates simple interest, total repayment, and annual payout using the formula A = P(1 + rt). - [Interest-Free Home Loan Calculator](https://justonlyonething.com/services/interest-free-home-loan/): Calculates the required monthly mutual fund SIP needed to earn returns that completely offset the total interest paid on a mortgage. - [Loan EMI Calculator](https://justonlyonething.com/services/emi-calculator/): Computes monthly loan installments (EMI), total interest payable, and annual amortization schedules for home loans, car loans, and personal loans. - [Home Loan Eligibility Calculator](https://justonlyonething.com/services/home-loan-eligibility/): Calculates maximum borrowing capacity based on monthly income, existing loan payments, and a 40%–50% Fixed Obligation to Income Ratio (FOIR). - [Startup Burn Rate & Runway Calculator](https://justonlyonething.com/services/startup-burn-rate/): Computes monthly gross burn, net burn, and cash runway in months by dividing cash balance by monthly net operating losses. - [Rental Yield & Income Calculator](https://justonlyonething.com/services/rental-yield/): Computes gross rental yield percentage, net rental yield after operating expenses, and capitalization rate (Cap Rate) for residential real estate. - [Net Worth Calculator](https://justonlyonething.com/services/net-worth-calculator/): Sums total liquid and physical assets minus short-term and long-term liabilities to calculate net worth and debt-to-asset ratios. - [Break-Even Calculator](https://justonlyonething.com/services/break-even-calculator/): Calculates unit sales and revenue needed to cover fixed costs using unit price, variable cost per unit, and contribution margin ratio. - [Profit Margin Calculator](https://justonlyonething.com/services/profit-margin-calculator/): Computes gross profit margin, operating profit margin (EBIT), net profit margin, and cost markup percentages from revenue and cost of goods sold. - [Working Capital Calculator](https://justonlyonething.com/services/working-capital-calculator/): Calculates net working capital, current ratio (Current Assets / Current Liabilities), and acid-test quick ratio to measure business liquidity. - [DSCR Calculator](https://justonlyonething.com/services/dscr-calculator/): Computes Debt Service Coverage Ratio (Net Operating Income / Annual Debt Service) to determine commercial loan repayment capacity. ## Developer Productivity Utilities (6 Tools) - [JSON Editor & Formatter Online](https://justonlyonething.com/services/json-editor/): Formats, validates syntax errors, repairs malformed keys, displays tree and table views, compares JSON diffs, and converts JSON to CSV in the browser. - [Base64 Encoder & Decoder](https://justonlyonething.com/services/base64-encoder-decoder/): Converts text and files between raw bytes, standard Base64 (RFC 4648 §4), and URL-safe Base64URL (RFC 4648 §5) with full UTF-8 support. - [RegEx Validator & Tester](https://justonlyonething.com/services/regex-validator/): Tests JavaScript regular expressions with real-time match highlighting, capture group extraction, and code generation for JavaScript, Python, Go, and Java. - [JWT Token Inspector & Debugger](https://justonlyonething.com/services/jwt-token-inspector/): Decodes JWT headers and payload claims without network requests, and verifies HMAC-SHA256 signatures client-side using the Web Crypto API. - [Cron Expression Parser & Schedule Generator](https://justonlyonething.com/services/cron-expression-parser/): Parses standard 5-field UNIX crontab and 6-field Quartz expressions into plain English sentences and calculates the next 10 upcoming run times. - [Hash & Cipher Generator](https://justonlyonething.com/services/hash-cipher-generator/): Computes MD5, SHA-1, SHA-256, SHA-384, SHA-512, RIPEMD-160, and CRC32 checksums, generates HMAC signatures, identifies unknown hash types, and encrypts text using AES-256-GCM. ## Editorial & Authorship - [About JustOnlyOneThing](https://justonlyonething.com/about/): Platform architectural philosophy, privacy guarantees, and technical background. - [Author Profile: Saurabh Passolia](https://justonlyonething.com/authors/saurabh-passolia/): Full-stack software engineer, personal finance practitioner, and creator of JustOnlyOneThing. - [The Symmetry of Code and Capital](https://justonlyonething.com/blog/why-developers-need-financial-discipline/): Technical essay exploring the mathematical parallels between software architecture, algorithmic scaling, and compound wealth creation.