Free, client-side utilities for the hex you stare at every day.
ATR, APDU, TLV, ASN.1, CBOR, ICCID, NDEF, SCP03 — all the parsers, decoders, and lookups that smart-card, secure-element, and telecom engineers reach for. No accounts. No ads. Nothing leaves your browser.
Need a searchable reference? Try the references section — APDU status words, EMV tags, AAGUIDs, COSE algorithms, X.509 OIDs, and more. Knowledge sharing belongs in the blog.
Architecture & diagrams
Sequence Diagram Generator
WebSequenceDiagrams syntax, SVG / PNG export, 7 built-in templates (FIDO2, SCP03, eSIM SGP.32, V2X PKI, UPI, banking MFA, device-identity lifecycle).
VIZPasskey Flow Visualizer
Interactive walk-through of WebAuthn registration and authentication.
Smart Card / JavaCard utilities
ATR Parser
Parse Answer-To-Reset bytes — TS, T0, TA/TB/TC/TD interface bytes, historical bytes, TCK.
APDUAPDU Parser
Decode CLA / INS / P1 / P2 / Lc / data / Le for Case 1–4, short and extended length.
TLVTLV Parser
Walk BER-TLV, EMV TLV, and DGI-TLV trees with tag dictionary lookup.
APDU Builder
Build a valid APDU from selected fields with live validation.
ASN.1 Decoder
Decode BER/DER blobs into a clickable tree with X.509 OID lookup.
BER/DERBER/DER Decoder
Same lower-level walker as the ASN.1 parser.
SWSW1/SW2 Lookup
Search status words by hex or phrase — ISO + GP + EMV + FIDO.
CAP File Inspector
Decode JavaCard CAP file components.
SCP03 Helper
Compute SCP03 session keys / cryptograms / MACs.
GP Status Reference
GlobalPlatform 2.3.1 card & application lifecycle states.
V2X / ITS PKI
IEEE 1609.2 V2X Certificate Parser
Client-side COER decoder for V2X / ITS certificates. Hex, Base64, or PEM input. Standards references on every field row.
CHAINV2X Certificate Chain Validator
End-entity → intermediate → root. HashedId8 linkage via WebCrypto SHA-256. Structural-only.
Certificates & PKI
X.509 Certificate Viewer
Decode subject, issuer, validity, public key, all extensions.
PEMPEM ↔ DER Converter
Convert certificates and keys between PEM and DER. Drag-and-drop, downloadable.
CSRPKCS#10 CSR Decoder
Decode subject, public key, requested extensions, signature.
FPCert Fingerprint Generator
SHA-1 / 256 / 384 / 512 of a cert’s DER. Web Crypto.
CHAINCertificate Chain Viewer
Walk a multi-cert PEM bundle; verify issuer→subject linkage.
B64Base64 Cert Decoder
Auto-detect PEM / base64 / hex; emit DER + clean PEM.
PFXPFX / PKCS#12 Inspector
Inspect bag types & encryption schemes inside a .pfx / .p12.
ASN.1ASN.1 Parser
Walk any BER/DER tree with OID lookup. Used by every cert tool.
Encoding & conversion
ASCII ↔ HEX
Bidirectional converter with multiple grouping styles.
HEXHEX ↔ byte array
Convert across C / Java / Python / JS / escape-string formats.
B64Base64
Encode / decode with URL-safe variant. UTF-8 friendly.
Base32
Encode / decode (RFC 4648).
UTF-8 inspector
Codepoints, byte counts, BOM detection, per-char view.
URL encoder
Percent-encode / decode.
Crypto & security helpers
CRC calculator
CRC-8 / CRC-16 / CRC-32 with polynomial picker.
LRC calculator
Longitudinal Redundancy Check.
Checksum
XOR / sum-mod-256 / two’s-complement.
SHA hash generator
SHA-1, SHA-256/384/512, SHA3 (via Web Crypto).
RSA key formats
PKCS#1 / PKCS#8 / SPKI / OpenSSH reference.
ECC curve reference
P-256, P-384, Curve25519, secp256k1, brainpool.
eSIM, SIM & telecom
ICCID Decoder
Issuer ID, country code, MII, Luhn check.
IMSI Decoder
MCC / MNC / MSIN.
ISO/IEC 7816 Reference
APDU shape, CLA bits, common INS bytes — bookmarkable.
SWAPDU Status Dictionary
Filterable full table — ISO 7816-4 + GP + EMV + FIDO.
eUICC EID Decoder
Per ITU-T E.118 / GSMA.
JSON / data utilities
JSON Formatter
Format, minify, error pinpointing.
JSON Validator
Schema-against-instance checker.
CBOR Parser
RFC 8949 decoder — FIDO/CTAP2 attestation friendly.
XML Formatter
Format and validate.
NFC & DESFire
DESFire Status Decoder
Look up DESFire response status bytes — OK, AUTH_ERROR, ADDITIONAL_FRAME, etc.
DESFireDESFire Access-Rights Decoder
Decode the 16-bit access-rights word into Read / Write / R+W / ChangeAR.
NDEFNDEF Decoder
URI, Text, Smart Poster, MIME, External (Android AAR) records.
UIDUID Analyzer
4 / 7 / 10-byte ISO 14443 Type A UIDs with manufacturer lookup.
ATSATS Parser
Decode ISO 14443-4 Answer-To-Select bytes.
14443ISO/IEC 14443 Reference
Parts, Type A/B, anti-collision, I/R/S blocks. One-page reference.
FIDO / WebAuthn
WebAuthn Reference
Developer-portal reference for registration / authentication / attestation, with copy-able code samples.
WebAuthnWebAuthn Attestation Decoder
Walk attestationObject — fmt / attStmt / authData — with verification checklist.
WebAuthnauthenticatorData Parser
Walk rpIdHash | flags | counter | AAGUID | credId | publicKey | extensions.
CBORCBOR Decoder
RFC 8949 walker. WebAuthn attestation, COSE keys, CTAP2 messages.
COSECOSE Key Inspector
Decode COSE_Key (RFC 8152) — kty / alg / crv / x / y / n / e.
AAGUIDAAGUID Lookup
Curated offline directory of well-known FIDO authenticators.
WebAuthnclientDataJSON Decoder
Decode type / challenge / origin / SHA-256 of the signed payload.
RP IDRP ID / Origin Validator
WebAuthn §5.1.3 registrable-suffix rule, HTTPS, PSL constraints.
WebAuthnCredential ID Inspector
Length, entropy, AAGUID-shaped prefix.
WebAuthnChallenge Viewer / Generator
Inspect challenge length and entropy. Generate fresh 32-byte challenges with the platform CSPRNG.
B64URLBase64URL Converter
RFC 4648 §5. The form WebAuthn / JOSE / CTAP2 use everywhere.
MDSFIDO Metadata Explorer
Browse the curated AAGUID directory in metadata-style cards. Searchable by vendor / model.
FLOWPasskey Flow Visualizer
Step-by-step walkthrough of registration and authentication ceremonies.
Smart-card developer tools
ISO 7816-4 CLA Decoder
Walk the bit-fields of CLA — SM, chaining, channel, type.
BERBER Length Visualizer
Decode and encode short / long / indefinite-form BER lengths.
EMVEMV Tag Dictionary
Filterable directory of EMV Books 3, 4, and CL tags.
DESFireKey Diversification Visualizer
Educational illustration of AES-CMAC diversification (NXP AN10922 / AV2).
SCP03SCP03 Session Walkthrough
Educational annotation of the GP 2.3.1 secure-channel protocol.
CMACCMAC Length Calculator
Block count, padded length, and standard truncation for AES / TDES CMAC.
SMSecure Messaging Field Visualizer
Walk SM-wrapped APDU body — DOs 87 / 97 / 99 / 8E / 84.
SCRIPTAPDU Script Validator
Multi-line APDU script validation. Validation only — no execution.
CAPJavaCard CAP Structure Explorer
Decode the 12 standard CAP file components. Header.cap walker.
ASN.1ASN.1 Tree Explorer
Collapsible DER walker with OID lookup. PEM input accepted.
TLVTLV Tree Visualizer
Visual companion to the TLV parser — collapsible nested tree with EMV tag lookup.
DESFire / Transit
DESFire Status Decoder
OK, AUTH_ERROR, ADDITIONAL_FRAME, etc.
DESFireAccess-Rights Decoder
Decode the 16-bit access-rights word.
DESFireFile Settings Parser
Decode the GetFileSettings response per file type.
DESFireKey Settings Interpreter
Decode the 2-byte GetKeySettings response.
TMACTransaction MAC Visualizer
EV2/EV3 TMAC field — TMC counter + TMV MAC.
14443ISO 14443 Frame Explorer
REQA, WUPA, ATQA, SAK, RATS, I-block / R-block / S-block.
Misc developer utilities
Binary Calculator
AND / OR / XOR / NOT / shift, multi-base.
Byte-offset Calculator
Quick parsing assistance.
Length-field Encoder
BER long-form, DGI long-form, u8, u16 BE / LE.
ENDEndian Converter
LE ↔ BE for u16/u32/u64 with grouped table view.
Everything runs in your browser.
Every tool runs entirely inside your browser. No inputs leave the page, no accounts, no logging, no analytics on tool inputs — privacy-first by design.