Developer Tools
Encode, decode, hash and test, with the browser's own engines, so results match your code exactly. Tokens, payloads and secrets are exactly what shouldn't touch third-party servers: here they never do.
- Base64 Encoder / Decoder Base64 turns any bytes into 64 safe characters, encode or decode instantly, with correct UTF-8 handling and the URL-safe variant.
- URL Encoder / Decoder Spaces become %20, & becomes %26, encode text safely into URLs, or decode percent-encoding back to readable text.
- HTML Entities Encoder / Decoder Turn < into < so it displays instead of rendering, or decode &-style entities back to plain text.
- SHA Hash Generator One input, four hashes, SHA-1, SHA-256, SHA-384 and SHA-512, computed by your browser’s built-in crypto engine.
- JWT Decoder Paste a JWT and read its header and payload instantly, with the expiry (exp) checked, all locally, which is the only safe way to inspect tokens.
- Regex Tester Type a pattern, paste test text, see every match with its position and capture groups, updated on every keystroke.
- Number Base Converter 255 = 0xff = 0o377 = 0b11111111, convert any number between bases 2, 8, 10 and 16, at any size, exactly.
- LLM Token Counter & Cost Calculator Paste a prompt, count its tokens, see the cost per model, exact OpenAI counts (the real tokenizer runs locally), clearly-labelled estimates for Claude and Gemini, a context-window fit bar, and cost math with a visible "prices last verified" date.
- Ethereum Unit Converter (Wei, Gwei, Ether) Convert between Ethereum units, wei, kwei, mwei, gwei, szabo, finney and ether, exactly, plus satoshi ⇄ BTC. No floating-point rounding, ever.
- Keccak-256 / SHA-3 Hash & Function Selector Hash text with Keccak-256 (the hash Ethereum actually uses) or NIST SHA3-256, shown side by side so you never confuse them, and compute a contract’s 4-byte function selector.
- EIP-55 Ethereum Address Checksum Check whether an Ethereum address has a valid EIP-55 checksum, and convert any address to its correct mixed-case form, the standard way wallets catch mistyped addresses.
- Query String Parser Paste a URL or query string to see its parameters as clean JSON, or switch to build mode to turn JSON into a query string.
- HTTP Status Code Lookup Enter one or more HTTP status codes to see their names, meanings and class (2xx success, 4xx client error, and so on).
- JSON String Escaper / Unescaper Turn raw text into a safe JSON string value, escaping ", \, newlines and tabs, or paste an escaped value to get the original text back.
- Unicode Escape Converter Turn accented letters, emoji and other non-ASCII characters into \uXXXX escapes, or paste \u escapes to get the readable text back.
- Text to Hex Converter Turn any text into its UTF-8 hex bytes, or paste hex (with or without spaces and 0x) to decode it back to readable text.
- JSON to TypeScript Paste a JSON object or array and get ready-to-use TypeScript interfaces, nested shapes become their own interfaces, missing keys become optional, and mixed arrays become unions.
- HAR File Viewer Drop a HAR file to see every request with its method, status, size and timing, plus a warning for any request that carries cookies, auth headers or token-like parameters.
- SQL Formatter Paste messy or minified SQL and get it pretty-printed with consistent indentation, line breaks and keyword casing, for the database dialect you choose.
- Base32 Encoder / Decoder Base32 encodes bytes using 32 case-insensitive characters (A, Z, 2-7), encode or decode instantly, with the base32hex variant.
- Ascii85 Encoder / Decoder Ascii85 packs 4 bytes into 5 printable characters, making it more compact than Base64, encode or decode instantly, with optional <~ ~> delimiters.
- Base58 Encoder / Decoder Base58 uses 58 characters with the look-alikes (0, O, I, l) removed, the encoding behind Bitcoin addresses and IPFS hashes. Encode or decode instantly.
- Base62 Encoder / Decoder Base62 uses only letters and digits (no +, / or =), making it safe for URLs and short IDs, encode or decode instantly.
- IBAN Validator & Formatter Paste an IBAN to check its ISO 13616 checksum and length and format it correctly, the number never leaves your device.
- ISBN-10 ↔ ISBN-13 Converter & Validator Paste an ISBN to verify its check digit and convert ISBN-10 ↔ ISBN-13, computed locally on your device.
- Punycode / IDN Converter Convert a Unicode domain (münchen.de) to its ASCII xn-- form and back, useful for DNS, email and spotting look-alike domains.
- JSON Diff / Compare Paste two JSON documents to see exactly what changed, a key-aware diff that ignores reformatting and key order.
- HMAC Generator Sign a message with a secret key to get its HMAC, the keyed hash used to verify webhooks and API requests, computed locally.
- JWT Encoder / Signer Create a signed JWT from your payload and secret, HS256/384/512, computed locally so the secret never leaves your browser.
- ISO 8601 Duration Converter ISO 8601 durations look like PT1H30M (1 hour 30 minutes). This converts them to seconds and HH:MM:SS, or turns seconds back into the string.
- UTM Campaign URL Builder Add utm_source, utm_medium and utm_campaign tags to any link so analytics can attribute the traffic, assembled and encoded correctly, live.
- JSON Schema Generator Paste a JSON example and get a draft-07 JSON Schema describing it, types, nested objects, arrays and required fields inferred for you.
- JSON to Go Struct Converter Paste JSON and get Go structs with the right field types and json:"…" tags, nested objects and slices handled for you.
- curl to JavaScript fetch Converter Paste a curl command and get the equivalent JavaScript fetch() call, method, headers, body and basic auth translated for you.
- JSON to Python Dataclass Converter Paste JSON and get Python @dataclass definitions with type hints, nested objects, lists and optional fields handled for you.
- JSON to Rust Struct Converter Paste JSON and get Rust structs deriving Serialize/Deserialize, types, Vec, nested structs and serde renames handled for you.
- JSON to C# Class Converter Paste JSON and get C# classes with properties and JsonPropertyName attributes, nested classes and List types handled for you.
- JSON to SQL INSERT Converter Paste a JSON array of objects and get ready-to-run SQL INSERT statements, numbers, booleans and NULLs typed, strings safely quoted.
- CSV to SQL INSERT Converter Paste CSV (with a header row) and get SQL INSERT statements, the header becomes the columns and each row an INSERT, safely quoted.
- SQL IN Clause Generator Paste a list and get a ready SQL IN (...) clause, strings quoted, numbers left bare, so you can drop it straight into a WHERE.
- Barcode Check Digit Validator (EAN, UPC, ISBN, ISSN) Paste a barcode, ISBN or ISSN and instantly see whether its check digit is correct, or enter the digits without it to get the complete number.
- IMEI & Luhn Validator Paste a 15-digit IMEI to verify its checksum and see its TAC and serial, or check any number against the Luhn algorithm.
- Snowflake ID Decoder Paste a Snowflake ID and pick the service to see exactly when it was created, plus the machine and sequence bits packed inside.
- CRC-32 & Adler-32 Checksum Calculator Type text or drop a file to get its CRC-32 (the ZIP/PNG checksum) and Adler-32 (zlib) values in hex and decimal.
- Protobuf Decoder (decode_raw) Paste protobuf bytes (hex or base64) to decode the message into its fields, numbers, wire types and values, with nested messages expanded.
- CBOR Decoder & Diagnostic Viewer Paste CBOR bytes (hex or base64) to see the decoded value as diagnostic notation and a typed tree, integers, strings, arrays, maps, tags and floats.
- IEEE 754 Floating-Point Converter See exactly how a number is stored as a float: the sign, exponent and mantissa bits for 16-, 32- and 64-bit IEEE 754, plus the rounding error.
- Email Header Analyzer Paste the full email headers to see the delivery route, the delay at each mail server, and the SPF, DKIM and DMARC results the receiver recorded.
- JWK Thumbprint Calculator (RFC 7638) Paste a JWK to get its RFC 7638 thumbprint and thumbprint URI, the canonical, stable fingerprint of the key.
Developer utilities that keep secrets local
These are the small, sharp tools you reach for a dozen times a day: Base64 and URL encoding, JSON and other formatters, hashes (SHA family via the browser's Web Crypto), JWT decoding, regex testing, an exact LLM token counter, and Ethereum helpers (BigInt-exact wei⇄ether, Keccak-256, EIP-55 checksums). Each does one job cleanly and shows its working.
Crucially, they run entirely in your browser, so pasting an API key, a private JWT, a config file or a wallet address never sends it to a server. That's the difference between a convenient tool and a liability: your secrets stay on your machine, and the tools keep working offline.
Frequently asked questions
Why does client-side matter especially for developer tools?
Because the inputs are secrets: JWTs are live credentials, Base64 blobs are often API payloads, and hashed strings can be keys. Pasting those into a server-backed tool hands them to that server. Every tool here runs locally, verify with the network tab or by going offline.
Do these tools match what my code does?
Yes, by construction: the regex tester runs the browser's actual RegExp engine, hashing uses the native Web Crypto implementation, and Base64/URL encoding use the platform functions with correct UTF-8 handling.
Why is there no MD5?
The Web Crypto API excludes it deliberately, MD5 collisions are practical, so it fails as a security primitive. SHA-256 is the modern default for everything MD5 used to do.