ASN.1 Tree Explorer
Walk DER-encoded ASN.1 bytes as a collapsible tree. Recognises primitive types (BOOLEAN, INTEGER, OID, OCTET STRING, UTF8String, etc.), surfaces OID names, and supports PEM input.
How to use this tool
What it does
Shows DER/ASN.1 as an interactive tree with tag classes, lengths and decoded values.
When to use it
Use it when an ASN.1 structure is deeply nested and you want to navigate rather than scroll.
Worked example
Expand a certificate's extensions node to inspect each OID and its value.
Input
Tree
About ASN.1
ASN.1 (ITU-T X.680) is the data-description language behind X.509, PKCS, CMS, SNMP, LDAP, and many telecom protocols. DER (X.690 §10) is the canonical binary encoding used in PKI and FIDO attestation.
Spec
ITU-T X.680 / X.690.
Companion
PFX / PKCS#12 inspector · ASN.1 parser (linear) · X.509 viewer
Frequently asked questions
What input does the explorer accept?
DER-encoded bytes as hex, or a PEM block — the BEGIN/END wrapper is stripped and the base64 decoded for you before parsing.
What is the difference between BER and DER?
BER allows several encodings of the same value; DER is the canonical subset that permits exactly one. Signatures are computed over DER precisely because it is unambiguous.
Why does the tree stop partway through my blob?
Almost always a length that overruns the remaining buffer, or a truncated file. The last node rendered marks where the encoding stops being self-consistent.
What do the tag numbers mean?
The identifier octet carries class, a constructed flag, and the tag number. 0x30 is a constructed SEQUENCE, 0x04 a primitive OCTET STRING, and 0xA0 a context-specific constructed element — the shape most certificate extensions use.
Does anything I paste leave my browser?
Nothing. The tool is entirely client-side: the page ships a static script, does no network calls, and never transmits what you paste. You can confirm it by opening the network tab, or by loading the page and then going offline.