Local developer tools

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• Inspect a payload or checksum while keeping it on your device.
• Review exact encodings, limits and unverified claims before using a result.

Read the selected tool’s instructions, supported formats and limits before starting. Review generated results before you use them.

18 tools that work now

• Text & code comparisonCompare exact lines and line endings. Download a complete local JSON report of additions and removals.
• Find & replace textReplace all literal or JavaScript regular-expression matches, with literal replacement text and local downloads.
• Regex testerTest JavaScript regular expressions locally and inspect complete matches, captures and UTF-16 offsets.
• Markdown previewPreview Markdown safely and export inert HTML. Images become alt text and links keep only their labels.
• Base64 encoder & decoderEncode UTF-8 text as Base64 or Base64url, or strictly decode it locally. Encoding is not encryption.
• URL encoder & decoderEncode or decode a URL component or form field value without opening a link.
• HTML entity encoder & decoderEscape markup characters or decode numeric references and six common named entities as plain text.
• JSON formatter & validatorFormat, minify, validate or inspect JSON paths while preserving original number spelling.
• JWT inspectorRead a JWT header and payload locally. Claims and signatures remain unverified.
• File & text checksumsCalculate MD5 or SHA checksums for exact local file bytes or UTF-8 text, with optional comparison.
• UUID, ULID & password generatorGenerate UUIDv4 identifiers, timestamped ULIDs or passwords with browser cryptographic randomness.
• Unix timestamp & timezoneConvert explicit Unix seconds, milliseconds or an offset-bearing ISO date and display an IANA time zone.
• Cron expression inspectorInspect numeric five-field cron schedules and find bounded upcoming matches in UTC. No task is scheduled.
• CSS unit converterConvert px, rem, em and vw using font sizes and viewport width you provide.
• Favicon & app icon packCreate nine PNG icon sizes, a PNG-backed ICO and a manifest starter from one local image.
• Image color & contrast checkerRead an oriented image pixel by coordinates and check an opaque sRGB pair against WCAG contrast thresholds.
• Barcode generatorCreate local Code128-B, checked UPC-A or DataMatrix ECC200 codes as self-contained SVG or PNG.
• Offline utilitiesOptionally save public code for supported local utilities and install the app. Your files and results are never cached.