Introduction
Converting Between JSON Schema and Zod: How required Maps to .optional()
Inside a two-way converter that turns JSON Schema into a Zod schema and Zod code back into JSON Schema. Covers the inverted defaults between required and .optional(), the constraint mapping table, and how the Zod side is parsed without executing any code.
How CREATE TABLE Generation From a Visual Table Design Works | DDL Builder
A look inside DDL Builder, which turns a visually designed table into CREATE TABLE statements and an ER diagram. Covers the MySQL/PostgreSQL/SQLite type-mapping rules and the column-inference algorithm used for JSON samples.
Case Converter: camelCase, snake_case & kebab-case — 9 Styles at Once
Convert identifiers between camelCase, PascalCase, snake_case, CONSTANT_CASE, kebab-case and more — all nine styles side by side. Handles acronym runs like HTTPServer, digits, and bulk multi-line conversion.
LLM API Cost Calculator: Compare Claude, GPT & Gemini Pricing Side by Side
Paste a prompt, set the expected output tokens, and compare per-request API costs across Claude, GPT and Gemini models. Covers input/output pricing structure, auto-updated price tables, and estimate limits.
AI Rules Generator: AGENTS.md, CLAUDE.md & Cursor Rules from One Form
Generate rules files for Claude Code, Cursor, GitHub Copilot, Windsurf and Gemini CLI in one shot. Covers the AGENTS.md standard, per-tool file formats, and why a single source of truth prevents rule drift.
LLM Token Counter: Check Claude, GPT & Gemini Token Counts in Your Browser
Paste text and compare token counts for Claude, GPT and Gemini side by side. Covers token basics, why tokenizers differ per model, why non-English text costs more tokens, and the limits of estimates.
IP/CIDR Subnet Calculator: Network, Broadcast & Mask at a Glance
How to calculate the network address, broadcast address, usable hosts, subnet mask and wildcard mask from CIDR notation like 192.168.1.10/24 — with a prefix-length cheat sheet.
How to Convert HEX, RGB, and HSL Colors and Check Contrast
Convert CSS color formats, adjust colors with HSL, and check foreground/background contrast for readable UI design.
Use Case
curl Options Cheat Sheet: What -X, -H and -d Actually Do
A reference for the curl options you meet in real API work: why -d already implies POST, how -d differs from --data-raw, the @ prefix that silently reads a file, single vs double quotes, and why -k and -L deserve more caution than they usually get.
SQL Clause Order Reference: Why WHERE Can't See Your SELECT Alias
The order you write SQL clauses is not the order the database runs them. A reference for the logical execution order (FROM → WHERE → GROUP BY → HAVING → SELECT → ORDER BY → LIMIT), why aliases fail in WHERE, when to use WHERE vs HAVING, and the MySQL/PostgreSQL differences that bite.
UTC to JST Reference: The 9-Hour Offset, Cheat Sheet & Timezone Pitfalls
Convert between UTC and JST (Japan Standard Time) with a cheat sheet. Covers what Z and +09:00 mean in ISO 8601, when JavaScript date parsing silently shifts by 9 hours, MySQL/PostgreSQL timezone behavior, and why GitHub Actions cron always runs in UTC.
Unified Diff Format Reference: Reading @@ Hunks in git diff Output
How to read the unified diff format git produces: what the four numbers in @@ -12,7 +12,9 @@ mean, why a one-character edit shows as a whole-line replacement, the whitespace and line-ending traps, \ No newline at end of file, combined @@@ diffs on merges, and rename detection via similarity index.
CREATE TABLE Reference: MySQL vs PostgreSQL vs SQLite Types & Constraints
A cross-database CREATE TABLE (DDL) reference with cheat sheets for data types, auto-increment keys (AUTO_INCREMENT / IDENTITY / rowid), foreign key ON DELETE behavior, and the CHECK constraint that MySQL silently ignores.
GitHub Actions needs Design Patterns: Speed Up CI, Avoid the Anti-Patterns
A pattern reference for GitHub Actions job dependencies (needs). Covers diamond-shaped fan-out, concurrency cancellation, fail-fast tradeoffs, matrix-plus-needs gotchas, and reusable workflows, with copy-paste YAML examples.
SQL JOIN Types: Complete Reference to INNER, LEFT, RIGHT & FULL
A reference for SQL JOIN types (INNER/LEFT/RIGHT/FULL/CROSS/SELF) with a cheat sheet and row-count walkthroughs. Covers why one-to-many joins duplicate rows, the WHERE-vs-ON NULL trap, and how to write multi-table joins.
AGENTS.md, CLAUDE.md, Cursor Rules: One Source of Truth for AI Coding Agents
Every AI coding agent wants its own rules file. Compare AGENTS.md, CLAUDE.md, .cursor/rules, copilot-instructions.md and more — what to write, a copy-paste template, and how to stop them drifting apart.
Purpose of this site
We gather technical knowledge and handy tools in one place so developers can shorten research time and focus on implementation.
Who is it for?
For engineers, developers, and technical leads who want quick verification tools and practical reference material.
Why is it useful?
Articles and tools are paired so you can understand a topic, then immediately try it in the browser.
Privacy-conscious tools
Tool input is processed locally whenever possible, helping you work with development data more safely.
Tools
AI & LLM
3 items
AI & LLM
Development & DevOps
9 items
Development & DevOps
GitHub Actions Visualizer
Visualize and build GitHub Actions workflow YAML with interactive diagrams in the browser.
SQL Formatter
Format and beautify SQL queries for various dialects (MySQL, PostgreSQL, etc.) instantly.
Visual SQL Builder
Construct complex SQL queries with SELECT, JOIN, and WHERE clauses using an intuitive visual GUI.
DDL Builder
Design tables and generate CREATE TABLE statements plus an ER diagram. Also infers columns from a JSON sample.
SQL → ER Diagram
Parse CREATE TABLE statements and automatically generate ER diagrams with relationships for visualization.
cURL Converter
Convert cURL commands to code in Python, Node, Go, Rust, and more.
chmod Calculator
Calculate and convert Linux file permissions between octal and symbolic formats with a visual UI.
Cron Editor & Parser
Parse Cron expressions into human-readable format and calculate next execution times for schedule verification.
Infrastructure Diagram Builder
Create system architecture and network diagrams with a GUI. Generate Mermaid code and images instantly.
Data Conversion & Schemas
6 items
Data Conversion & Schemas
JSON Formatter
Pretty-print or minify JSON for quick validation of payloads and logs.
JSON → TypeScript
Generate TypeScript interfaces from JSON instantly for API responses and configs, including optional/null hints.
JSON → Zod
Infer Zod schemas from sample JSON for parsing or runtime validation and share contracts quickly.
JSON → OpenAPI
Generate OpenAPI component schemas from example JSON in the browser to prep review-ready drafts.
JSON ⇔ YAML
Paste JSON or YAML and convert both ways with copy helpers for config or docs handoffs.
CSV ⇔ JSON Converter
Convert between CSV and JSON formats with support for custom delimiters and headers.
Security & Cryptography
5 items
Security & Cryptography
Base64 / 58 / 32
Switch tabs to encode or decode with any base in one place while comparing lengths and URL safety.
JWT Tool
Create and decode HS256-signed tokens in the browser without sending keys out of your session.
Hash & HMAC Generator
Generate SHA-1, SHA-256, SHA-512 hashes and HMAC signatures instantly in the browser for secure data verification.
JWKS Generator
Build RSA key pairs, publish public JWKS, and sign RS256 JWTs locally to rehearse key rotation.
UUID Generator
Generate UUIDv4 identifiers and copy instantly for tests or collision checks.
Text & Code Helpers
5 items
Text & Code Helpers
Markdown Table Generator
Create and edit Markdown tables visually with CSV import/export and column alignment controls.
Text & Code Suite
Count text, escape HTML/XML, minify CSS/JS, and generate passwords for quick publishing checks.
Regex Tester
Validate patterns, flags, and captured groups in one view to mirror production-like tests.
Diff Viewer
Visualize text changes with inline highlighting to confirm edits before commits or reviews.
Case Converter
Convert identifiers to camelCase, snake_case, kebab-case, and more at once.
URL, QR & Network
5 items
URL, QR & Network
URL Encode / Decode
Encode or decode URLs without leaving your browser to catch slug issues or encoding gaps.
IP / CIDR Calculator
Compute the network, broadcast, host range, host count and masks from CIDR notation.
URL Params → JSON
Turn query strings into JSON objects for quick inspection when debugging APIs or webhooks.
QR Generator
Turn any text or URL into a QR code and save as PNG for sharing Wi‑Fi setups or quick links.
QR Reader
Scan codes with the browser camera and decode locally without sending images to a server.
Design & UI
2 items
Design & UI
Date & Time
3 items
Date & Time
Time Zone Converter
Swap between any two time zones instantly (default UTC and JST) to sanity-check launch, meeting, or deploy times.
Time Units
Convert milliseconds through weeks at once and compare results for TTLs, delays, and retry windows.
UNIX Timestamp Converter
Convert UNIX timestamps (seconds or milliseconds) to UTC and local time instantly to validate logs and alerts.