Regex, cron, timestamps, URL encoding and code formatters are the daily tools of every developer. The 5 most important things to know:
(?<name>) not (?P<name>).Date.now() returns milliseconds.encodeURIComponent() for query parameter values, never encodeURI().The best developer tools are the ones that are always available — no installation, no account, no waiting. This guide covers the everyday utilities that developers reach for dozens of times a week: testing a regular expression, building a cron schedule, converting a timestamp, encoding a URL, or formatting a SQL query. Each tool runs entirely in your browser, processing your data locally without sending it to any server.
Regular expressions (regex) are one of the most powerful tools in a developer's toolkit. A regex pattern can validate an email address, extract data from a log file, or perform complex search-and-replace operations in a single line of code.
JavaScript regex flavour: Our Regex Tester uses JavaScript's built-in RegExp engine, the standard for web development and Node.js.
Flags: g (global), i (case insensitive), m (multiline), s (dotall), u (Unicode). For most use cases, gi is the right combination.
Capture groups: (pattern) captures a group; (?:pattern) groups without capturing; (?<name>pattern) names the capture.
Common patterns: Email: /^[\w.-]+@[\w.-]+\.[a-z]{2,}$/i. UUID: /[0-9a-f]{8}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{12}/i.
A standard cron expression has 5 fields: minute (0–59), hour (0–23), day of month (1–31), month (1–12), and day of week (0–7).
Special characters: * means every value. */n means every nth value. a-b means a range. a,b,c means specific values.
Common schedules — every minute: * * * * * daily at midnight UTC: 0 0 * * * every Monday at 9am: 0 9 * * 1 every weekday at 6pm: 0 18 * * 1-5.
6-field cron: AWS EventBridge, Spring Boot, and Quartz add a seconds field. Our Cron Expression Generator supports both 5-field and 6-field variants.
Timezone gotcha: Cloud schedulers (AWS EventBridge, GitHub Actions schedules) run in UTC. A job set to fire at 9am local time will fire at a different UTC hour depending on DST.
A Unix timestamp counts seconds elapsed since January 1, 1970, 00:00:00 UTC. It is the universal language for representing moments in time in APIs, databases, and log files.
Seconds vs milliseconds: A 10-digit number is almost certainly seconds (e.g., 1700000000 = November 2023). A 13-digit number is milliseconds. JavaScript's Date.now() returns milliseconds; Python's time.time() returns seconds. Our Timestamp Converter auto-detects the precision.
The Year 2038 problem: 32-bit signed integers can represent timestamps only up to January 19, 2038. Systems storing timestamps in 32-bit integers will overflow on that date. 64-bit systems can represent timestamps until the year 292 billion.
ISO 8601 for human-readable timestamps: Always use ISO 8601 format (2024-01-15T10:30:00Z) in JSON payloads and log files. Avoid locale-specific formats like 01/15/2024.
URLs can only contain a limited set of ASCII characters directly. Characters outside this set must be percent-encoded: replaced by a % followed by their two-digit hex code. Space becomes %20, & becomes %26.
encodeURI vs encodeURIComponent: encodeURI() encodes a full URL, preserving characters with structural meaning. encodeURIComponent() encodes a URL component (a single query parameter value), encoding nearly everything including & and =.
The most common bug: Using encodeURI() on a query parameter value, which leaves & unencoded and breaks the query string. Always use encodeURIComponent() for individual parameter values.
Double encoding: Encoding an already-encoded string produces %2520 instead of %20. Decode once before re-encoding if you are unsure whether the input is already encoded.
가장 흔한 두 가지 원인은 다음과 같습니다: Python의 re 모듈은 다른 정규식 방식을 사용하며, 명명된 그룹의 구문이 다릅니다 — JavaScript에서는 (?P<name>)를 (?<name>)로 바꾸세요.
*/15 9-17 * * 1-5를 사용하세요. */15는 0, 15, 30, 45분에 실행되고, 9-17은 업무 시간으로 제한하며, 1-5는 월요일부터 금요일까지로 제한합니다. Cron Generator를 사용하여 이를 시각적으로 만들고 검증하세요.
Timestamp Converter를 사용하세요 — 현재 타임스탬프가 실시간으로 업데이트되어 표시됩니다. 코드에서: JavaScript는 초 단위로 Math.floor(Date.now() / 1000)를, Python은 import time; time.time()을 사용합니다.
& 문자는 쿼리 문자열 구분자입니다. 매개변수 값에 리터럴 &가 포함되어 있으면 %26으로 퍼센트 인코딩해야 합니다. URL Encoder의 component 모드를 사용하여 개별 매개변수 값을 올바르게 인코딩하세요.
한 가지 스타일을 정하고 linter로 강제하세요. 가장 일반적인 관례는 키워드를 대문자로(SELECT, FROM, WHERE) 작성하고 각 절을 별도의 줄에 두는 것입니다. SQL Formatter는 일관된 포맷을 적용하며 키워드 대소문자 설정을 지원합니다.