diff --git a/src/wire/varint.h b/src/wire/varint.h
new file mode 100644
index 0000000..a1da93d
--- /dev/null
+++ b/src/wire/varint.h
@@ -0,0 +1,30 @@
+// varint.h
+// QUIC variable-length integers, according to RFC 9000 Section 16.
+//
+// The top two bits of the first byte indicate the length of the integer in bytes:
+// 00: 1 byte (6 bits of data)
+// 01: 2 bytes (14 bits of data)
+// 10: 4 bytes (30 bits of data)
+// 11: 8 bytes (62 bits of data)
+// The remaining bits of the first byte, along with the subsequent bytes, contain the integer value in big-endian order.
+// Values above BRAVAIS_VARINT_MAX are not able to be incoded.
+
+#ifndef BRAVAIS_VARINT_H
+#define BRAVAIS_VARINT_H
+
+#include <stddef.h>
+#include <stdint.h>
+
+#include "util/buf.h"
+
+#define BRAVAIS_VARINT_MAX UINT64_C(0x3FFFFFFFFFFFFFFF)
+
+// Bytes needed to encode *val*, or 0 if *val* is too large to encode (>BRAVAIS_VARINT_MAX).
+size_t bravais_varint_len(uint64_t val);
+
+uint64_t bravais_rcur_varint(bravais_rcur_buf_t* buf);
+
+// Always uses the shortest encoding. Fails the cursor if value is too large.
+void bravais_wcur_varint(bravais_wcur_t* cur, uint64_t val);
+
+#endif // BRAVAIS_VARINT_H