Protocols & Binary Serialization
Paste one complete BER or DER value, choose its text encoding, then decode the TLV tree.
Enter bytes or load the example.
Bytes stay in this browser; no upload or URL storage.
Enter bytes or load the example.
Use this ASN.1 decoder when a certificate, CSR or key blob fails in another parser and you need to see where the bytes actually stop. A readable certificate summary can hide a malformed length or a trailing octet; the raw structure cannot.
The ASN.1 decoder also provides a single-TLV builder for checking identifier and length encoding. It treats application and context tags as numbered tags, because their business meaning needs an external schema.
Inspect the exact encoded structure before assigning it a certificate meaning.
The ASN.1 decoder shows every node’s start offset, header size and content length. A declared length beyond its parent, a missing BER terminator or bytes after the root becomes a concrete error rather than a partial success.
Enter complete tag bytes and raw value bytes; the builder writes the definite length and passes the generated bytes through the same parser. Constructed tags require complete child TLVs, so a plausible-looking invalid payload is rejected.
Hex is the default. Switch explicitly to PEM or Base64 for textual wrappers; a local DER file is read as bytes. This avoids mistaking hex that also happens to be valid Base64.
Decoding is manual. Compare the selected node’s tag class, start offset, header length and content length with the source. BER indefinite lengths are accepted only on constructed values.
The build view writes a definite length from the value bytes. Use “Decode generated TLV” to preview replacing your decode input, then apply or undo the replacement.
Hex, Base64 and one PEM block are selected deliberately; local DER files never need to pass through a text encoding. The ASN.1 decoder reports malformed input before walking its tree.
INTEGER, OID, strings and other clear universal types get a readable preview. Every selected node still exposes its tag and original content hex, including unknown application tags.
Constructed definite and indefinite BER values can nest, with a 256 KiB input, 32-level depth and 10,000-node ceiling. These limits keep damaged or hostile lengths from monopolizing the tab.
A certificate decoder names X.509 fields. This ASN.1 decoder shows generic tag, length, value and offset for any single BER/DER root, but does not assign certificate meaning or verify trust.
BER permits a constructed value to run until an end-of-contents marker. DER forbids that form. The tree marks it as indefinite and requires the closing bytes.
A context-specific tag number is only an identifier. Its meaning comes from the surrounding ASN.1 schema, which this generic viewer does not infer.
No. The local file and pasted bytes are read in this browser, with no network request or URL fragment containing the input.
Yes, choose PEM and paste one matching BEGIN/END block. A chain containing multiple blocks is rejected, so select the one value you want to inspect.
Still have a question?
Paste one BER/DER value or open a local file, then check each boundary before treating it as a higher-level object.
Parsing runs in this browser.