Expand or compress IPv6 addresses
Switch between compressed (::1) and fully-expanded IPv6 forms. Useful for logs, configs, and matching exact addresses across systems.
0000:0000:0000:0000:0000:0000:0000:0001
How to convert an IPv6 address
IPv6 addresses are 128 bits, written as eight 4-hex groups. Long runs of zeros can be collapsed to :: exactly once per address.
- 01
Pick a direction
Expand fills in zeros; compress collapses the longest zero run.
Bytes flow through
TextEncoder/TextDecoderfor predictable UTF-8 semantics — emoji, surrogate pairs, and combining marks all encode losslessly.modeUTF-8TextEncoderlosslesslivemode · raw bytesset · UTF-8expand / compress
loaded · UTF-8MIME · ready - 02
Paste the address
Anything from
::1to a full eight-group form.Hash and signature operations call
crypto.subtlefrom the Web Crypto API, so output matches OpenSSL / Node bit-for-bit.inputWeb Cryptosubtledeterministicliveinput · optionsipv6 · live::1
options applied · livelive - 03
Read the canonical form
Output is lowercase with leading-zero padding (expand) or collapsed (compress).
Options re-run instantly through
useEffect+useMemo— switching URL-safe mode or padding doesn’t re-encode from scratch.canonmemoisedoptionsinstantreactiveout · encodedform · ready0000:0000:…:0001
encoded · livelossless - 04
Copy or download
Use the canonical form for logs, configs, or matching.
Copy uses the Async Clipboard API; downloads ship via
Blobwith the appropriate MIME (text/plain,image/png, …) so external tools recognise them.exportclipboardblobMIME-correctclient-sideok · copiedready · doneCopied
shipped · ready to shipsuccess
Encoding without surprises
Always UTF-8 first
Use TextEncoder / TextDecoder for bytes ↔ string conversion. btoa alone breaks on non-ASCII.
URL-safe vs standard Base64
Standard uses +, /, =; URL-safe swaps to -, _, no padding. Don’t mix them.
Hashes aren’t passwords
SHA-256 is fast; that’s good for fingerprints, bad for passwords. Use bcrypt / argon2 for credentials.
Watch padding rules
Some decoders are strict about = padding, others auto-pad. If round-trips fail at exactly 1 or 2 bytes, check padding.
Use Web Crypto for keys
Generate cryptographic keys via crypto.subtle, never Math.random. The latter is predictable.
JWT decode ≠ verify
Decoding a JWT just splits and base64-decodes. Verification needs the issuer’s public key / shared secret.
When to canonicalise IPv6
Log matching, firewall rules, DNS records, debugging.
Log matching
Different systems write IPv6 differently — canonicalise first. Output round-trips losslessly with the matching decoder — both run client-side, so end-to-end testing happens in a single tab. Encoding flows through TextEncoder for predictable UTF-8 semantics.
RFC-compliantFirewall rules
Match exact addresses regardless of how they're written. Web Crypto's subtle.digest produces output that matches OpenSSL, GPG, and Node's crypto module byte-for-byte. That makes the result trustworthy as a content fingerprint, ETag, or integrity check.
OpenSSL-matchedDNS AAAA records
Confirm the address you're publishing is correct. Pairs cleanly with HMAC, JWT, and signed-URL workflows where bit-level correctness matters. The browser's crypto stack is FIPS 140-validated in Chrome and Firefox, so it's production-grade.
losslessDebugging
Spot identical addresses with different shorthand. Output uses canonical RFC 4648 / 7515 alphabets so curl, openssl, and any standards-compliant decoder accept it as input. URL-safe variants drop padding for tokens that travel in query strings.
byte-identicalMigration
Standardise addresses moving from one format to another. Heavy hashing runs through useMemo so large inputs don't block typing. PBKDF2, bcrypt, and Argon2 expose configurable cost factors — tune for your threat model, not the default.
spec-gradeDocumentation
Always document the expanded canonical form. Same input plus same options always yields identical bytes. That's the foundation for content-addressed storage (IPFS, Git, S3 ETags) and means the output is safe to commit to fixtures.
production-readyFrequently asked questions
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