ASN.1 Decoder Decode ASN.1 DER/BER structures from PEM, Base64, or hex.

What Is ASN.1 Decoder?

Decodes ASN.1 DER/BER binary structures displaying tag-length-value tree. Recognizes SEQUENCE, SET, INTEGER, BIT STRING, OCTET STRING, OID, and string types. Accepts PEM, Base64, or hex input. Essential for X.509 certificates and PKCS keys. All client-side.

Why Use ASN.1 Decoder?

• PEM/Base64/hex input
• Common ASN.1 types
• Hierarchical display
• 100% client-side

Common Use Cases

Certificates

X.509 structure.

Keys

PKCS structures.

Protocols

ASN.1 messages.

Education

Encoding rules.

Technical Guide

TLV parsing: 0x02=INTEGER, 0x30=SEQUENCE, 0x06=OID, etc. Constructed types (bit 5) parsed recursively to depth 10. Length: short (0-127), long (0x80|n).

Tips & Best Practices

• 1
  Works with X.509, PKCS
• 2
  PEM headers stripped
• 3
  Recursive parsing
• 4
  Values truncated

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Frequently Asked Questions

Q Is it free?

Yes.

Q What input formats are supported?

PEM/Base64/hex.

Q Can it decode X.509 certificates?

Yes.

Q Is my data safe?

Yes.

Q What ASN.1 types are supported?

SEQUENCE, INTEGER, OID, etc.

About This Tool

ASN.1 Decoder is a free online tool by FreeToolkit.ai. All processing happens directly in your browser — your data never leaves your device. No registration or installation required.