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.
Las dos causas más comunes son: el módulo re de Python usa una variante de regex diferente, y los grupos con nombre usan una sintaxis distinta — traduce (?P<name>) a (?<name>) para JavaScript.
Usa */15 9-17 * * 1-5. El */15 se ejecuta en los minutos 0, 15, 30 y 45; 9-17 lo limita al horario laboral; 1-5 lo limita de lunes a viernes. Usa nuestro Generador de Cron para construirlo y verificarlo visualmente.
Usa nuestro Conversor de Marcas de Tiempo — muestra la marca de tiempo actual actualizándose en tiempo real. En código: JavaScript usa Math.floor(Date.now() / 1000) para los segundos, Python usa import time; time.time().
El carácter & es el delimitador de la cadena de consulta. Si el valor de tu parámetro contiene un & literal, debe codificarse como porcentaje con %26. Usa el modo de componente de nuestro Codificador de URL para codificar correctamente los valores de cada parámetro.
Elige un estilo y aplícalo con un linter. La convención más común es palabras clave en MAYÚSCULAS (SELECT, FROM, WHERE) con cada cláusula en su propia línea. Nuestro Formateador de SQL aplica un formato consistente y admite el uso configurable de mayúsculas en las palabras clave.