diff --git a/age/format/format.ha b/age/format/format.ha
new file mode 100644
index 0000000..f7f1b2e
--- /dev/null
+++ b/age/format/format.ha
@@ -0,0 +1,155 @@
+use os;
+use bufio;
+use strings;
+use fmt;
+use encoding::base64;
+use io;
+
+def INTRO: str = "age-encryption.org/v1";
+def STANZA_PREFIX: str = "->";
+def FOOTER_PREFIX: str = "---";
+
+def COLUMNS_PER_LINE: size = 64;
+def BYTES_PER_LINE: size = COLUMNS_PER_LINE / 4 * 3;
+
+export type stanza = struct {
+    recipient_type: str,
+    args: []str,
+    body: []u8,
+};
+
+export type header = struct {
+    mac: [32]u8,
+	recipients: []stanza,
+};
+
+export type parse_error = !void;
+
+fn is_valid_string(s: str) bool = {
+	if (len(s) == 0) {
+		return false;
+	};
+	for (let char .. strings::toutf8(s)) {
+		if (char < 33 || char > 126) {
+			return false;
+		};
+	};
+	return true;
+};
+
+fn read_stanza(scanner: *bufio::scanner) (stanza | parse_error) = {
+	const line = match (bufio::scan_string(scanner, "\n")!) {
+		case io::EOF =>
+			return fmt::fatal("unexpected end of file");
+		case let line: str =>
+			yield line;
+	};
+	if (!strings::hasprefix(line, STANZA_PREFIX)) {
+		return fmt::fatalf("malformed stanza opening line: {}", line);
+	};
+	
+	const (prefix, args): (str, []str) = split_args(line);
+	if (prefix != STANZA_PREFIX || len(args) < 1) {
+		return fmt::fatalf("malformed stanza: {}", line);
+	};
+	
+	for (let arg .. args) {
+		if (!is_valid_string(arg)) {
+			return fmt::fatalf("malformed stanza: {}", line);
+		};
+	};
+
+	const recipient_type = args[0];
+	const args = args[1..];
+	let body: []u8 = [];
+	
+	for (true) {
+		const next_line = match (bufio::scan_string(scanner, "\n")!) {
+			case io::EOF =>
+				return fmt::fatal("unexpected end of file");
+			case let line: str =>
+				yield line;
+		};
+		const b = decode_string(next_line)!;
+		
+		if (len(b) > BYTES_PER_LINE) {
+			return fmt::fatalf("malformed body line {}: too long", next_line);
+		};
+		
+		append(body, b...)!;
+		if (len(b) < BYTES_PER_LINE) {
+			// stanza bodies always end with short lines
+			return stanza{
+				recipient_type = recipient_type,
+				args = args,
+				body = body
+			};
+		};
+		
+	};
+};
+
+fn split_args(line: str) (str, []str) = {
+	const parts = strings::split(line, " ")!;
+	return (parts[0], parts[1..]);
+};
+
+fn decode_string(encoded: str) ([]u8 | parse_error) = {
+	if (strings::contains(encoded, "\n", "\r")) {
+		return fmt::fatalf("unexpected newline character");
+	};
+	return base64::decodestr(&base64::std_encoding, encoded)!;
+};
+
+export fn parse(path: str) ((header, bufio::scanner) | parse_error) = {
+    const file = os::open(path)!;
+    const scanner = bufio::newscanner(file);
+
+	let recipients: []stanza = [];
+
+	const version_line = match (bufio::scan_string(&scanner, "\n")!) {
+	case io::EOF =>
+		return fmt::fatal("unexpected end of file");
+	case let line: str =>
+		yield line;
+	};
+	if (version_line != "age-encryption.org/v1") {
+		return fmt::fatalf("unexpected intro: {}", version_line);
+	};
+	let header_mac: [32]u8 = [0...];
+	for (true) {
+		const next_line = match (bufio::scan_line(&scanner)!) {
+			case io::EOF =>
+				return fmt::fatal("unexpected end of file");
+			case let line: str =>
+				yield line;
+		};
+
+		if (strings::fromutf8(strings::toutf8(next_line)[0..3])! == FOOTER_PREFIX) {
+			// we're at the footer line
+			const (prefix, args) = split_args(next_line);
+			if (prefix != FOOTER_PREFIX || len(args) != 1) {
+				return fmt::fatalf("malformed closing line: {}", next_line);
+			};
+
+			const mac = decode_string(args[0])!;
+			if (len(mac) != 32) {
+				return fmt::fatalf("malformed closing line: {}", next_line);
+			};
+			// io::copy(&memio::fixed(header_mac), &memio::fixed(mac))!;
+			header_mac[..] = mac[0..32];
+			break;
+		};
+		bufio::unread(&scanner, strings::toutf8(next_line));
+
+		const found_stanza = read_stanza(&scanner)!;
+		append(recipients, found_stanza)!;
+	};
+	const prefix = bufio::scan_buffer(&scanner);
+	bufio::unread(&scanner, prefix);
+
+	return (header{
+		mac = header_mac,
+		recipients = recipients,
+	}, scanner);
+};
\ No newline at end of file