diff --git a/src/inspector/termio.zig b/src/inspector/termio.zig
index 9f55e6019..934bb6e2d 100644
--- a/src/inspector/termio.zig
+++ b/src/inspector/termio.zig
@@ -286,18 +286,19 @@ pub const VTEvent = struct {
             ),
 
             else => switch (Value) {
-                u8, u16 => try md.put(
-                    key,
-                    try std.fmt.allocPrintSentinel(alloc, "{}", .{value}, 0),
-                ),
-
                 []const u8,
                 [:0]const u8,
                 => try md.put(key, try alloc.dupeZ(u8, value)),
 
-                else => |T| {
-                    @compileLog(T);
-                    @compileError("unsupported type, see log");
+                else => |T| switch (@typeInfo(T)) {
+                    .int => try md.put(
+                        key,
+                        try std.fmt.allocPrintSentinel(alloc, "{}", .{value}, 0),
+                    ),
+                    else => {
+                        @compileLog(T);
+                        @compileError("unsupported type, see log");
+                    },
                 },
             },
         }
diff --git a/src/terminal/osc.zig b/src/terminal/osc.zig
index 1f4489961..14d501eaa 100644
--- a/src/terminal/osc.zig
+++ b/src/terminal/osc.zig
@@ -14,6 +14,8 @@ const Allocator = mem.Allocator;
 const LibEnum = @import("../lib/enum.zig").Enum;
 const kitty_color = @import("kitty/color.zig");
 const parsers = @import("osc/parsers.zig");
+const encoding = @import("osc/encoding.zig");
+
 pub const color = parsers.color;
 
 const log = std.log.scoped(.osc);
@@ -191,6 +193,9 @@ pub const Command = union(Key) {
     /// ConEmu GUI macro (OSC 9;6)
     conemu_guimacro: [:0]const u8,
 
+    /// Kitty text sizing protocol (OSC 66)
+    kitty_text_sizing: parsers.kitty_text_sizing.OSC,
+
     pub const Key = LibEnum(
         if (build_options.c_abi) .c else .zig,
         // NOTE: Order matters, see LibEnum documentation.
@@ -216,6 +221,7 @@ pub const Command = union(Key) {
             "conemu_progress_report",
             "conemu_wait_input",
             "conemu_guimacro",
+            "kitty_text_sizing",
         },
     );
 
@@ -342,6 +348,7 @@ pub const Parser = struct {
         @"2",
         @"4",
         @"5",
+        @"6",
         @"7",
         @"8",
         @"9",
@@ -358,6 +365,7 @@ pub const Parser = struct {
         @"21",
         @"22",
         @"52",
+        @"66",
         @"77",
         @"104",
         @"110",
@@ -431,6 +439,7 @@ pub const Parser = struct {
             .prompt_start,
             .report_pwd,
             .show_desktop_notification,
+            .kitty_text_sizing,
             => {},
         }
 
@@ -510,6 +519,7 @@ pub const Parser = struct {
                 '2' => self.state = .@"2",
                 '4' => self.state = .@"4",
                 '5' => self.state = .@"5",
+                '6' => self.state = .@"6",
                 '7' => self.state = .@"7",
                 '8' => self.state = .@"8",
                 '9' => self.state = .@"9",
@@ -600,7 +610,14 @@ pub const Parser = struct {
                 else => self.state = .invalid,
             },
 
-            .@"52" => switch (c) {
+            .@"6" => switch (c) {
+                '6' => self.state = .@"66",
+                else => self.state = .invalid,
+            },
+
+            .@"52",
+            .@"66",
+            => switch (c) {
                 ';' => self.writeToAllocating(),
                 else => self.state = .invalid,
             },
@@ -685,6 +702,10 @@ pub const Parser = struct {
 
             .@"52" => parsers.clipboard_operation.parse(self, terminator_ch),
 
+            .@"6" => null,
+
+            .@"66" => parsers.kitty_text_sizing.parse(self, terminator_ch),
+
             .@"77" => null,
 
             .@"133" => parsers.semantic_prompt.parse(self, terminator_ch),
@@ -696,4 +717,5 @@ pub const Parser = struct {
 
 test {
     _ = parsers;
+    _ = encoding;
 }
diff --git a/src/terminal/osc/encoding.zig b/src/terminal/osc/encoding.zig
new file mode 100644
index 000000000..7491d10c2
--- /dev/null
+++ b/src/terminal/osc/encoding.zig
@@ -0,0 +1,38 @@
+//! Specialized encodings used in some OSC protocols.
+const std = @import("std");
+
+/// Kitty defines "Escape code safe UTF-8" as valid UTF-8 with the
+/// additional requirement of not containing any C0 escape codes
+/// (0x00-0x1f), DEL (0x7f) and C1 escape codes (0x80-0x9f).
+///
+/// Used by OSC 66 (text sizing) and OSC 99 (Kitty notifications).
+///
+/// See: https://sw.kovidgoyal.net/kitty/desktop-notifications/#safe-utf8
+pub fn isSafeUtf8(s: []const u8) bool {
+    const utf8 = std.unicode.Utf8View.init(s) catch {
+        @branchHint(.cold);
+        return false;
+    };
+
+    var it = utf8.iterator();
+    while (it.nextCodepoint()) |cp| switch (cp) {
+        0x00...0x1f, 0x7f, 0x80...0x9f => {
+            @branchHint(.cold);
+            return false;
+        },
+        else => {},
+    };
+
+    return true;
+}
+
+test isSafeUtf8 {
+    const testing = std.testing;
+
+    try testing.expect(isSafeUtf8("Hello world!"));
+    try testing.expect(isSafeUtf8("安全的ユニコード☀️"));
+    try testing.expect(!isSafeUtf8("No linebreaks\nallowed"));
+    try testing.expect(!isSafeUtf8("\x07no bells"));
+    try testing.expect(!isSafeUtf8("\x1b]9;no OSCs\x1b\\\x1b[m"));
+    try testing.expect(!isSafeUtf8("\x9f8-bit escapes are clever, but no"));
+}
diff --git a/src/terminal/osc/parsers.zig b/src/terminal/osc/parsers.zig
index 152276af2..9c1c39b2c 100644
--- a/src/terminal/osc/parsers.zig
+++ b/src/terminal/osc/parsers.zig
@@ -6,6 +6,7 @@ pub const clipboard_operation = @import("parsers/clipboard_operation.zig");
 pub const color = @import("parsers/color.zig");
 pub const hyperlink = @import("parsers/hyperlink.zig");
 pub const kitty_color = @import("parsers/kitty_color.zig");
+pub const kitty_text_sizing = @import("parsers/kitty_text_sizing.zig");
 pub const mouse_shape = @import("parsers/mouse_shape.zig");
 pub const osc9 = @import("parsers/osc9.zig");
 pub const report_pwd = @import("parsers/report_pwd.zig");
@@ -19,6 +20,7 @@ test {
     _ = color;
     _ = hyperlink;
     _ = kitty_color;
+    _ = kitty_text_sizing;
     _ = mouse_shape;
     _ = osc9;
     _ = report_pwd;
diff --git a/src/terminal/osc/parsers/kitty_text_sizing.zig b/src/terminal/osc/parsers/kitty_text_sizing.zig
new file mode 100644
index 000000000..2c2d1b8fd
--- /dev/null
+++ b/src/terminal/osc/parsers/kitty_text_sizing.zig
@@ -0,0 +1,250 @@
+//! Kitty's text sizing protocol (OSC 66)
+//! Specification: https://sw.kovidgoyal.net/kitty/text-sizing-protocol/
+
+const std = @import("std");
+const build_options = @import("terminal_options");
+
+const assert = @import("../../../quirks.zig").inlineAssert;
+
+const Parser = @import("../../osc.zig").Parser;
+const Command = @import("../../osc.zig").Command;
+const encoding = @import("../encoding.zig");
+const lib = @import("../../../lib/main.zig");
+const lib_target: lib.Target = if (build_options.c_abi) .c else .zig;
+
+const log = std.log.scoped(.kitty_text_sizing);
+
+pub const max_payload_length = 4096;
+
+pub const VAlign = lib.Enum(lib_target, &.{
+    "top",
+    "bottom",
+    "center",
+});
+
+pub const HAlign = lib.Enum(lib_target, &.{
+    "left",
+    "right",
+    "center",
+});
+
+pub const OSC = struct {
+    scale: u3 = 1, // 1 - 7
+    width: u3 = 0, // 0 - 7 (0 means default)
+    numerator: u4 = 0,
+    denominator: u4 = 0,
+    valign: VAlign = .top,
+    halign: HAlign = .left,
+    text: [:0]const u8,
+
+    /// We don't currently support encoding this to C in any way.
+    pub const C = void;
+
+    pub fn cval(_: OSC) C {
+        return {};
+    }
+
+    fn update(self: *OSC, key: u8, value: []const u8) !void {
+        // All values are numeric, so we can do a small hack here
+        const v = try std.fmt.parseInt(u4, value, 10);
+
+        switch (key) {
+            's' => {
+                if (v == 0) return error.InvalidValue;
+                self.scale = std.math.cast(u3, v) orelse return error.Overflow;
+            },
+            'w' => self.width = std.math.cast(u3, v) orelse return error.Overflow,
+            'n' => self.numerator = v,
+            'd' => self.denominator = v,
+            'v' => self.valign = std.enums.fromInt(VAlign, v) orelse return error.InvalidValue,
+            'h' => self.halign = std.enums.fromInt(HAlign, v) orelse return error.InvalidValue,
+            else => return error.UnknownKey,
+        }
+    }
+};
+
+pub fn parse(parser: *Parser, _: ?u8) ?*Command {
+    assert(parser.state == .@"66");
+
+    const writer = parser.writer orelse {
+        parser.state = .invalid;
+        return null;
+    };
+
+    // Write a NUL byte to ensure that `text` is NUL-terminated
+    writer.writeByte(0) catch {
+        parser.state = .invalid;
+        return null;
+    };
+    const data = writer.buffered();
+
+    const payload_start = std.mem.indexOfScalar(u8, data, ';') orelse {
+        log.warn("missing semicolon before payload", .{});
+        parser.state = .invalid;
+        return null;
+    };
+    const payload = data[payload_start + 1 .. data.len - 1 :0];
+
+    // Payload has to be a URL-safe UTF-8 string,
+    // and be under the size limit.
+    if (payload.len > max_payload_length) {
+        log.warn("payload is too long", .{});
+        parser.state = .invalid;
+        return null;
+    }
+    if (!encoding.isSafeUtf8(payload)) {
+        log.warn("payload is not escape code safe UTF-8", .{});
+        parser.state = .invalid;
+        return null;
+    }
+
+    parser.command = .{
+        .kitty_text_sizing = .{ .text = payload },
+    };
+    const cmd = &parser.command.kitty_text_sizing;
+
+    // Parse any arguments if given
+    if (payload_start > 0) {
+        var kv_it = std.mem.splitScalar(
+            u8,
+            data[0..payload_start],
+            ':',
+        );
+
+        while (kv_it.next()) |kv| {
+            var it = std.mem.splitScalar(u8, kv, '=');
+            const k = it.next() orelse {
+                log.warn("missing key", .{});
+                continue;
+            };
+            if (k.len != 1) {
+                log.warn("key must be a single character", .{});
+                continue;
+            }
+
+            const value = it.next() orelse {
+                log.warn("missing value", .{});
+                continue;
+            };
+
+            cmd.update(k[0], value) catch |err| {
+                switch (err) {
+                    error.UnknownKey => log.warn("unknown key: '{c}'", .{k[0]}),
+                    else => log.warn("invalid value for key '{c}': {}", .{ k[0], err }),
+                }
+                continue;
+            };
+        }
+    }
+
+    return &parser.command;
+}
+
+test "OSC 66: empty parameters" {
+    const testing = std.testing;
+
+    var p: Parser = .init(null);
+
+    const input = "66;;bobr";
+    for (input) |ch| p.next(ch);
+
+    const cmd = p.end('\x1b').?.*;
+    try testing.expect(cmd == .kitty_text_sizing);
+    try testing.expectEqual(1, cmd.kitty_text_sizing.scale);
+    try testing.expectEqualStrings("bobr", cmd.kitty_text_sizing.text);
+}
+
+test "OSC 66: single parameter" {
+    const testing = std.testing;
+
+    var p: Parser = .init(null);
+
+    const input = "66;s=2;kurwa";
+    for (input) |ch| p.next(ch);
+
+    const cmd = p.end('\x1b').?.*;
+    try testing.expect(cmd == .kitty_text_sizing);
+    try testing.expectEqual(2, cmd.kitty_text_sizing.scale);
+    try testing.expectEqualStrings("kurwa", cmd.kitty_text_sizing.text);
+}
+
+test "OSC 66: multiple parameters" {
+    const testing = std.testing;
+
+    var p: Parser = .init(null);
+
+    const input = "66;s=2:w=7:n=13:d=15:v=1:h=2;long";
+    for (input) |ch| p.next(ch);
+
+    const cmd = p.end('\x1b').?.*;
+    try testing.expect(cmd == .kitty_text_sizing);
+    try testing.expectEqual(2, cmd.kitty_text_sizing.scale);
+    try testing.expectEqual(7, cmd.kitty_text_sizing.width);
+    try testing.expectEqual(13, cmd.kitty_text_sizing.numerator);
+    try testing.expectEqual(15, cmd.kitty_text_sizing.denominator);
+    try testing.expectEqual(.bottom, cmd.kitty_text_sizing.valign);
+    try testing.expectEqual(.center, cmd.kitty_text_sizing.halign);
+    try testing.expectEqualStrings("long", cmd.kitty_text_sizing.text);
+}
+
+test "OSC 66: scale is zero" {
+    const testing = std.testing;
+
+    var p: Parser = .init(null);
+
+    const input = "66;s=0;nope";
+    for (input) |ch| p.next(ch);
+    const cmd = p.end('\x1b').?.*;
+
+    try testing.expect(cmd == .kitty_text_sizing);
+    try testing.expectEqual(1, cmd.kitty_text_sizing.scale);
+}
+
+test "OSC 66: invalid parameters" {
+    const testing = std.testing;
+
+    var p: Parser = .init(null);
+
+    for ("66;w=8:v=3:n=16;") |ch| p.next(ch);
+    const cmd = p.end('\x1b').?.*;
+
+    try testing.expect(cmd == .kitty_text_sizing);
+    try testing.expectEqual(0, cmd.kitty_text_sizing.width);
+    try testing.expect(cmd.kitty_text_sizing.valign == .top);
+    try testing.expectEqual(0, cmd.kitty_text_sizing.numerator);
+}
+
+test "OSC 66: UTF-8" {
+    const testing = std.testing;
+
+    var p: Parser = .init(null);
+
+    const input = "66;;👻魑魅魍魉ゴースッティ";
+    for (input) |ch| p.next(ch);
+
+    const cmd = p.end('\x1b').?.*;
+    try testing.expect(cmd == .kitty_text_sizing);
+    try testing.expectEqualStrings("👻魑魅魍魉ゴースッティ", cmd.kitty_text_sizing.text);
+}
+
+test "OSC 66: unsafe UTF-8" {
+    const testing = std.testing;
+
+    var p: Parser = .init(null);
+
+    const input = "66;;\n";
+    for (input) |ch| p.next(ch);
+
+    try testing.expect(p.end('\x1b') == null);
+}
+
+test "OSC 66: overlong UTF-8" {
+    const testing = std.testing;
+
+    var p: Parser = .init(null);
+
+    const input = "66;;" ++ "bobr" ** 1025;
+    for (input) |ch| p.next(ch);
+
+    try testing.expect(p.end('\x1b') == null);
+}
diff --git a/src/terminal/stream.zig b/src/terminal/stream.zig
index eef249327..74a01e8a6 100644
--- a/src/terminal/stream.zig
+++ b/src/terminal/stream.zig
@@ -2107,6 +2107,7 @@ pub fn Stream(comptime Handler: type) type {
                 .conemu_change_tab_title,
                 .conemu_wait_input,
                 .conemu_guimacro,
+                .kitty_text_sizing,
                 => {
                     log.debug("unimplemented OSC callback: {}", .{cmd});
                 },