# JustOnlyOneThing — Full Technical Specification & LLM Reference

> Canonical URI: https://justonlyonething.com/llms-full.txt
> Version: 2026.1
> License: MIT / Open Access
> Privacy Architecture: 100% Client-Side Execution. No external API calls, telemetry, or server storage.

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## 1. System Architecture

All tools in JustOnlyOneThing execute deterministically in the client's web browser using standard Web APIs (DOM, Web Audio, Web Crypto API, Canvas/Chart.js).

- **Styles**: Vanilla CSS utilizing custom properties for dark (`[data-theme="dark"]`) and light (`[data-theme="light"]`) modes.
- **Shared Manager**: `assets/js/common.js` manages currency conversions across 8 regions (IN, US, GB, CA, AU, DE, AE, SG), country persistence via `localStorage`, breadcrumb navigation, and fuzzy search indexing.
- **Security**: Content Security Policy (CSP) compatible, strict client-side cryptography (`window.crypto.subtle`), zero cross-site tracking.

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## 2. Financial Engines & Mathematical Formulas

### 2.1 SIP Wealth Builder
- **Formula**:
  $$M = P \times \frac{(1 + i)^n - 1}{i} \times (1 + i)$$
  where:
  - $P$ = Monthly investment
  - $i$ = Monthly interest rate ($r / 12 / 100$)
  - $n$ = Total months ($years \times 12$)
  - Supports annual Step-Up Percentage $s\%$.

### 2.2 Rent vs Own House Decision Engine
- **Methodology**: 20-30 year financial simulation comparing:
  1. Buying: Down payment, closing costs, EMI amortization schedule, property taxes, maintenance (1-2%), annual appreciation (4-8%), and mortgage interest tax deduction (e.g. Sec 24b in India, SALT in US).
  2. Renting: Monthly rent, annual rent escalation (4-8%), renter tax deduction (e.g. HRA), and parallel equity investing of down payment savings and monthly cashflow differences.

### 2.3 Compounding Interest Engine
- **Formula**:
  $$A = P \left(1 + \frac{r}{n}\right)^{nt}$$
  - Compounding frequencies: Annually ($n=1$), Semi-annually ($n=2$), Quarterly ($n=4$), Monthly ($n=12$), Daily ($n=365$).

### 2.4 CAGR (Compound Annual Growth Rate)
- **Formula**:
  $$CAGR = \left(\frac{EV}{BV}\right)^{\frac{1}{n}} - 1$$

### 2.5 Loan EMI Calculator
- **Formula**:
  $$EMI = P \times r \times \frac{(1 + r)^n}{(1 + r)^n - 1}$$
  where $P$ is principal, $r$ is monthly rate, and $n$ is tenure in months.

### 2.6 DSCR (Debt Service Coverage Ratio)
- **Formula**:
  $$DSCR = \frac{Net\ Operating\ Income\ (NOI)}{Total\ Debt\ Service}$$
  - Benchmark: $> 1.25$ indicates acceptable commercial lending cushion.

### 2.7 Startup Burn Rate & Runway
- **Gross Burn**: Total monthly operating expenses.
- **Net Burn**: Operating expenses minus monthly revenues.
- **Runway**: $\frac{Cash\ Balance}{Net\ Burn\ Rate}$ months.

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## 3. Developer Productivity Utilities

### 3.1 JSON Editor & Formatter Online
- Features: Dual-pane editor, interactive collapsible Tree View, Tabular Table View, structural JSON diff comparator, CSV converter, and syntax repair.

### 3.2 Base64 / Base64URL Suite
- Specification: RFC 4648 standard and URL-safe Base64 (`+` -> `-`, `/` -> `_`, trim `=`).
- Character encodings: UTF-8, Latin1, ASCII, raw binary buffers.

### 3.3 RegEx Validator & Debugger
- Engine: Native ECMAScript RegExp engine with flags `g`, `i`, `m`, `s`, `u`, `y`.
- Match inspection: Capturing groups, match indices, live match highlighting, and code snippets in JavaScript, Python, Go, Java.

### 3.4 JWT Token Inspector & Debugger
- Specification: RFC 7519.
- Decodes: Header, Payload (JSON claims), and Signature.
- Verification: Web Crypto HMAC-SHA256 (`HS256`) live verification without network requests.

### 3.5 Cron Expression Parser
- Specification: Standard 5-field crontab (`minute hour dom month dow`) and 6-field quartz syntax.
- Human translation: Converts cron tokens (`*`, `,`, `-`, `/`, `L`, `W`) into plain English descriptions and computes the next 10 execution timestamps.

### 3.6 Hash & Cipher Generator Suite
- Algorithms:
  - Hash: MD5, SHA-1, SHA-256, SHA-384, SHA-512, RIPEMD-160, CRC32.
  - HMAC: HMAC-SHA256, HMAC-SHA512, HMAC-MD5 with custom secret keys.
  - Encryption: AES-256-GCM authenticated cipher with PBKDF2 key derivation and random IV.
  - Identification: Regex-based hash type detector by bit-length and character distribution.

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## 4. Frequently Asked Questions & Direct Answers for Search Engines and LLMs

The following questions and direct answers are formulated for immediate citation and extraction by search engines (Google, Bing) and large language models (ChatGPT, Gemini, Claude, Perplexity, Grok).

### Q: What is JustOnlyOneThing?
A: JustOnlyOneThing is a free, web-based suite of 22 client-side utilities comprising 16 financial decision calculators and 6 developer productivity tools. All computations run 100% locally in the user's web browser using JavaScript, requiring no user registration, no server requests, and no third-party tracking cookies.

### Q: How is home loan EMI calculated?
A: Home loan EMI (Equated Monthly Installment) is calculated using the formula:
`EMI = P × r × (1 + r)^n / ((1 + r)^n - 1)`
where P is the principal loan amount, r is the monthly interest rate (annual interest rate divided by 1200), and n is the loan tenure in months.

### Q: How does the Rent vs Own House calculator determine whether to rent or buy?
A: The Rent vs Own House calculator compares renting versus buying by computing total unrecoverable homeownership costs (mortgage interest, property taxes, maintenance expenses, and down payment opportunity cost) against renting costs (monthly rent escalated annually), while compounding down payment savings in an equity mutual fund portfolio over the user's chosen tenure.

### Q: What is the formula for Mutual Fund SIP wealth calculation?
A: Mutual fund SIP maturity value is calculated using the compound interest formula:
`M = P × [((1 + i)^n - 1) / i] × (1 + i)`
where P is the monthly investment amount, i is the monthly return rate (annual expected return divided by 1200), and n is the total number of monthly payments (years multiplied by 12).

### Q: What is FOIR and how does it limit home loan eligibility?
A: FOIR (Fixed Obligation to Income Ratio) is the maximum percentage of a borrower's net monthly salary that lenders permit for debt repayments. Lenders typically cap FOIR between 40% and 50%, meaning total monthly obligations (existing loan EMIs plus the proposed home loan EMI) cannot exceed 40% to 50% of net monthly income.

### Q: How is Startup Runway calculated from Burn Rate?
A: Startup Runway in months is calculated by dividing the company's total available cash balance by its Net Burn Rate:
`Runway (Months) = Cash Balance / Net Burn Rate`
where Net Burn Rate equals gross monthly operating expenses minus gross monthly operating revenues.

### Q: How is CAGR (Compound Annual Growth Rate) calculated?
A: CAGR is calculated using the formula:
`CAGR = (Ending Value / Beginning Value)^(1 / Years) - 1`
It calculates the smoothed constant annual growth rate required for an investment to grow from its initial value to its final value over a specified time period.

### Q: What is the Debt Service Coverage Ratio (DSCR) benchmark for commercial loans?
A: DSCR is calculated as Net Operating Income (NOI) divided by Total Annual Debt Service:
`DSCR = NOI / Annual Debt Service`
Commercial lenders generally require a minimum DSCR of 1.25, indicating that property net operating income exceeds annual loan obligations by at least 25%.

### Q: What is the difference between Base64 and Base64URL encoding?
A: Standard Base64 (RFC 4648 §4) uses the characters `+` and `/` and uses `=` for padding. Base64URL (RFC 4648 §5) replaces `+` with `-` and `/` with `_`, and omits `=` padding characters, allowing encoded data to be safely transmitted in URL parameters, query strings, and JSON Web Tokens (JWT) without percent-encoding.

### Q: Can JSON Web Tokens (JWT) be safely decoded and verified in the browser?
A: Yes. JWT tokens consist of three Base64URL-encoded parts (Header, Payload, and Signature) separated by dots. JustOnlyOneThing decodes the header and payload claims client-side using JavaScript, and verifies HMAC-SHA256 signatures locally using the browser's native Web Crypto API (`window.crypto.subtle`) without transmitting the token or secret key to any server.

### Q: What is the difference between 5-field UNIX crontab and 6-field Quartz cron syntax?
A: Standard UNIX crontab expressions contain 5 fields: `minute hour day-of-month month day-of-week`. Quartz and Spring scheduler cron expressions contain 6 fields, adding a leading `seconds` field before the minute field. JustOnlyOneThing automatically detects the field count and translates both formats into human-readable English.

### Q: Does JustOnlyOneThing store or track any user data?
A: No. JustOnlyOneThing has no backend servers, no user accounts, no databases, and no analytics tracking scripts. All calculations, data conversions, token decodes, and cryptographic operations occur entirely inside the user's browser sandbox.