diff --git a/proto/protovalidate-testing/buf/validate/conformance/cases/strings.proto b/proto/protovalidate-testing/buf/validate/conformance/cases/strings.proto
index f590c2de..a0fa9268 100644
--- a/proto/protovalidate-testing/buf/validate/conformance/cases/strings.proto
+++ b/proto/protovalidate-testing/buf/validate/conformance/cases/strings.proto
@@ -196,6 +196,12 @@ message StringTUUID {
 message StringNotTUUID {
   string val = 1 [(buf.validate.field).string.tuuid = false];
 }
+message StringULID {
+  string val = 1 [(buf.validate.field).string.ulid = true];
+}
+message StringNotULID {
+  string val = 1 [(buf.validate.field).string.ulid = false];
+}
 message StringHttpHeaderName {
   string val = 1 [(buf.validate.field).string.well_known_regex = KNOWN_REGEX_HTTP_HEADER_NAME];
 }
@@ -223,6 +229,12 @@ message StringUUIDIgnore {
     (buf.validate.field).ignore = IGNORE_IF_ZERO_VALUE
   ];
 }
+message StringULIDIgnore {
+  string val = 1 [
+    (buf.validate.field).string = {ulid: true},
+    (buf.validate.field).ignore = IGNORE_IF_ZERO_VALUE
+  ];
+}
 message StringInOneof {
   oneof foo {
     string bar = 1 [(buf.validate.field).string = {
diff --git a/proto/protovalidate/buf/validate/validate.proto b/proto/protovalidate/buf/validate/validate.proto
index 519545dd..5faf6e73 100644
--- a/proto/protovalidate/buf/validate/validate.proto
+++ b/proto/protovalidate/buf/validate/validate.proto
@@ -3731,6 +3731,31 @@ message StringRules {
       }
     ];
 
+    // `ulid` specifies that the field value must be a valid ULID (Universally Unique
+    // Lexicographically Sortable Identifier) as defined by the [ULID specification](https://github.com/ulid/spec).
+    // ULID is a 26-character Base32-encoded string using Crockford's Base32 alphabet
+    // (0-9, A-Z excluding I, L, O, U). If the field value isn't a valid ULID, an error
+    // message will be generated.
+    //
+    // ```proto
+    // message MyString {
+    //   // value must be a valid ULID
+    //   string value = 1 [(buf.validate.field).string.ulid = true];
+    // }
+    // ```
+    bool ulid = 35 [
+      (predefined).cel = {
+        id: "string.ulid"
+        message: "value must be a valid ULID"
+        expression: "!rules.ulid || this == '' || this.matches('^[0-9A-HJKMNP-TV-Za-hjkmnp-tv-z]{26}$')"
+      },
+      (predefined).cel = {
+        id: "string.ulid_empty"
+        message: "value is empty, which is not a valid ULID"
+        expression: "!rules.ulid || this != ''"
+      }
+    ];
+
     // `well_known_regex` specifies a common well-known pattern
     // defined as a regex. If the field value doesn't match the well-known
     // regex, an error message will be generated.
diff --git a/tools/internal/gen/buf/validate/conformance/cases/strings.pb.go b/tools/internal/gen/buf/validate/conformance/cases/strings.pb.go
index 6a9bfff1..e0a83778 100644
--- a/tools/internal/gen/buf/validate/conformance/cases/strings.pb.go
+++ b/tools/internal/gen/buf/validate/conformance/cases/strings.pb.go
@@ -2324,6 +2324,94 @@ func (x *StringNotTUUID) GetVal() string {
 	return ""
 }
 
+type StringULID struct {
+	state         protoimpl.MessageState `protogen:"open.v1"`
+	Val           string                 `protobuf:"bytes,1,opt,name=val,proto3" json:"val,omitempty"`
+	unknownFields protoimpl.UnknownFields
+	sizeCache     protoimpl.SizeCache
+}
+
+func (x *StringULID) Reset() {
+	*x = StringULID{}
+	mi := &file_buf_validate_conformance_cases_strings_proto_msgTypes[52]
+	ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
+	ms.StoreMessageInfo(mi)
+}
+
+func (x *StringULID) String() string {
+	return protoimpl.X.MessageStringOf(x)
+}
+
+func (*StringULID) ProtoMessage() {}
+
+func (x *StringULID) ProtoReflect() protoreflect.Message {
+	mi := &file_buf_validate_conformance_cases_strings_proto_msgTypes[52]
+	if x != nil {
+		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
+		if ms.LoadMessageInfo() == nil {
+			ms.StoreMessageInfo(mi)
+		}
+		return ms
+	}
+	return mi.MessageOf(x)
+}
+
+// Deprecated: Use StringULID.ProtoReflect.Descriptor instead.
+func (*StringULID) Descriptor() ([]byte, []int) {
+	return file_buf_validate_conformance_cases_strings_proto_rawDescGZIP(), []int{52}
+}
+
+func (x *StringULID) GetVal() string {
+	if x != nil {
+		return x.Val
+	}
+	return ""
+}
+
+type StringNotULID struct {
+	state         protoimpl.MessageState `protogen:"open.v1"`
+	Val           string                 `protobuf:"bytes,1,opt,name=val,proto3" json:"val,omitempty"`
+	unknownFields protoimpl.UnknownFields
+	sizeCache     protoimpl.SizeCache
+}
+
+func (x *StringNotULID) Reset() {
+	*x = StringNotULID{}
+	mi := &file_buf_validate_conformance_cases_strings_proto_msgTypes[53]
+	ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
+	ms.StoreMessageInfo(mi)
+}
+
+func (x *StringNotULID) String() string {
+	return protoimpl.X.MessageStringOf(x)
+}
+
+func (*StringNotULID) ProtoMessage() {}
+
+func (x *StringNotULID) ProtoReflect() protoreflect.Message {
+	mi := &file_buf_validate_conformance_cases_strings_proto_msgTypes[53]
+	if x != nil {
+		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
+		if ms.LoadMessageInfo() == nil {
+			ms.StoreMessageInfo(mi)
+		}
+		return ms
+	}
+	return mi.MessageOf(x)
+}
+
+// Deprecated: Use StringNotULID.ProtoReflect.Descriptor instead.
+func (*StringNotULID) Descriptor() ([]byte, []int) {
+	return file_buf_validate_conformance_cases_strings_proto_rawDescGZIP(), []int{53}
+}
+
+func (x *StringNotULID) GetVal() string {
+	if x != nil {
+		return x.Val
+	}
+	return ""
+}
+
 type StringHttpHeaderName struct {
 	state         protoimpl.MessageState `protogen:"open.v1"`
 	Val           string                 `protobuf:"bytes,1,opt,name=val,proto3" json:"val,omitempty"`
@@ -2333,7 +2421,7 @@ type StringHttpHeaderName struct {
 
 func (x *StringHttpHeaderName) Reset() {
 	*x = StringHttpHeaderName{}
-	mi := &file_buf_validate_conformance_cases_strings_proto_msgTypes[52]
+	mi := &file_buf_validate_conformance_cases_strings_proto_msgTypes[54]
 	ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
 	ms.StoreMessageInfo(mi)
 }
@@ -2345,7 +2433,7 @@ func (x *StringHttpHeaderName) String() string {
 func (*StringHttpHeaderName) ProtoMessage() {}
 
 func (x *StringHttpHeaderName) ProtoReflect() protoreflect.Message {
-	mi := &file_buf_validate_conformance_cases_strings_proto_msgTypes[52]
+	mi := &file_buf_validate_conformance_cases_strings_proto_msgTypes[54]
 	if x != nil {
 		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
 		if ms.LoadMessageInfo() == nil {
@@ -2358,7 +2446,7 @@ func (x *StringHttpHeaderName) ProtoReflect() protoreflect.Message {
 
 // Deprecated: Use StringHttpHeaderName.ProtoReflect.Descriptor instead.
 func (*StringHttpHeaderName) Descriptor() ([]byte, []int) {
-	return file_buf_validate_conformance_cases_strings_proto_rawDescGZIP(), []int{52}
+	return file_buf_validate_conformance_cases_strings_proto_rawDescGZIP(), []int{54}
 }
 
 func (x *StringHttpHeaderName) GetVal() string {
@@ -2377,7 +2465,7 @@ type StringHttpHeaderValue struct {
 
 func (x *StringHttpHeaderValue) Reset() {
 	*x = StringHttpHeaderValue{}
-	mi := &file_buf_validate_conformance_cases_strings_proto_msgTypes[53]
+	mi := &file_buf_validate_conformance_cases_strings_proto_msgTypes[55]
 	ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
 	ms.StoreMessageInfo(mi)
 }
@@ -2389,7 +2477,7 @@ func (x *StringHttpHeaderValue) String() string {
 func (*StringHttpHeaderValue) ProtoMessage() {}
 
 func (x *StringHttpHeaderValue) ProtoReflect() protoreflect.Message {
-	mi := &file_buf_validate_conformance_cases_strings_proto_msgTypes[53]
+	mi := &file_buf_validate_conformance_cases_strings_proto_msgTypes[55]
 	if x != nil {
 		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
 		if ms.LoadMessageInfo() == nil {
@@ -2402,7 +2490,7 @@ func (x *StringHttpHeaderValue) ProtoReflect() protoreflect.Message {
 
 // Deprecated: Use StringHttpHeaderValue.ProtoReflect.Descriptor instead.
 func (*StringHttpHeaderValue) Descriptor() ([]byte, []int) {
-	return file_buf_validate_conformance_cases_strings_proto_rawDescGZIP(), []int{53}
+	return file_buf_validate_conformance_cases_strings_proto_rawDescGZIP(), []int{55}
 }
 
 func (x *StringHttpHeaderValue) GetVal() string {
@@ -2421,7 +2509,7 @@ type StringHttpHeaderNameLoose struct {
 
 func (x *StringHttpHeaderNameLoose) Reset() {
 	*x = StringHttpHeaderNameLoose{}
-	mi := &file_buf_validate_conformance_cases_strings_proto_msgTypes[54]
+	mi := &file_buf_validate_conformance_cases_strings_proto_msgTypes[56]
 	ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
 	ms.StoreMessageInfo(mi)
 }
@@ -2433,7 +2521,7 @@ func (x *StringHttpHeaderNameLoose) String() string {
 func (*StringHttpHeaderNameLoose) ProtoMessage() {}
 
 func (x *StringHttpHeaderNameLoose) ProtoReflect() protoreflect.Message {
-	mi := &file_buf_validate_conformance_cases_strings_proto_msgTypes[54]
+	mi := &file_buf_validate_conformance_cases_strings_proto_msgTypes[56]
 	if x != nil {
 		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
 		if ms.LoadMessageInfo() == nil {
@@ -2446,7 +2534,7 @@ func (x *StringHttpHeaderNameLoose) ProtoReflect() protoreflect.Message {
 
 // Deprecated: Use StringHttpHeaderNameLoose.ProtoReflect.Descriptor instead.
 func (*StringHttpHeaderNameLoose) Descriptor() ([]byte, []int) {
-	return file_buf_validate_conformance_cases_strings_proto_rawDescGZIP(), []int{54}
+	return file_buf_validate_conformance_cases_strings_proto_rawDescGZIP(), []int{56}
 }
 
 func (x *StringHttpHeaderNameLoose) GetVal() string {
@@ -2465,7 +2553,7 @@ type StringHttpHeaderValueLoose struct {
 
 func (x *StringHttpHeaderValueLoose) Reset() {
 	*x = StringHttpHeaderValueLoose{}
-	mi := &file_buf_validate_conformance_cases_strings_proto_msgTypes[55]
+	mi := &file_buf_validate_conformance_cases_strings_proto_msgTypes[57]
 	ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
 	ms.StoreMessageInfo(mi)
 }
@@ -2477,7 +2565,7 @@ func (x *StringHttpHeaderValueLoose) String() string {
 func (*StringHttpHeaderValueLoose) ProtoMessage() {}
 
 func (x *StringHttpHeaderValueLoose) ProtoReflect() protoreflect.Message {
-	mi := &file_buf_validate_conformance_cases_strings_proto_msgTypes[55]
+	mi := &file_buf_validate_conformance_cases_strings_proto_msgTypes[57]
 	if x != nil {
 		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
 		if ms.LoadMessageInfo() == nil {
@@ -2490,7 +2578,7 @@ func (x *StringHttpHeaderValueLoose) ProtoReflect() protoreflect.Message {
 
 // Deprecated: Use StringHttpHeaderValueLoose.ProtoReflect.Descriptor instead.
 func (*StringHttpHeaderValueLoose) Descriptor() ([]byte, []int) {
-	return file_buf_validate_conformance_cases_strings_proto_rawDescGZIP(), []int{55}
+	return file_buf_validate_conformance_cases_strings_proto_rawDescGZIP(), []int{57}
 }
 
 func (x *StringHttpHeaderValueLoose) GetVal() string {
@@ -2509,7 +2597,7 @@ type StringUUIDIgnore struct {
 
 func (x *StringUUIDIgnore) Reset() {
 	*x = StringUUIDIgnore{}
-	mi := &file_buf_validate_conformance_cases_strings_proto_msgTypes[56]
+	mi := &file_buf_validate_conformance_cases_strings_proto_msgTypes[58]
 	ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
 	ms.StoreMessageInfo(mi)
 }
@@ -2521,7 +2609,7 @@ func (x *StringUUIDIgnore) String() string {
 func (*StringUUIDIgnore) ProtoMessage() {}
 
 func (x *StringUUIDIgnore) ProtoReflect() protoreflect.Message {
-	mi := &file_buf_validate_conformance_cases_strings_proto_msgTypes[56]
+	mi := &file_buf_validate_conformance_cases_strings_proto_msgTypes[58]
 	if x != nil {
 		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
 		if ms.LoadMessageInfo() == nil {
@@ -2534,7 +2622,7 @@ func (x *StringUUIDIgnore) ProtoReflect() protoreflect.Message {
 
 // Deprecated: Use StringUUIDIgnore.ProtoReflect.Descriptor instead.
 func (*StringUUIDIgnore) Descriptor() ([]byte, []int) {
-	return file_buf_validate_conformance_cases_strings_proto_rawDescGZIP(), []int{56}
+	return file_buf_validate_conformance_cases_strings_proto_rawDescGZIP(), []int{58}
 }
 
 func (x *StringUUIDIgnore) GetVal() string {
@@ -2544,6 +2632,50 @@ func (x *StringUUIDIgnore) GetVal() string {
 	return ""
 }
 
+type StringULIDIgnore struct {
+	state         protoimpl.MessageState `protogen:"open.v1"`
+	Val           string                 `protobuf:"bytes,1,opt,name=val,proto3" json:"val,omitempty"`
+	unknownFields protoimpl.UnknownFields
+	sizeCache     protoimpl.SizeCache
+}
+
+func (x *StringULIDIgnore) Reset() {
+	*x = StringULIDIgnore{}
+	mi := &file_buf_validate_conformance_cases_strings_proto_msgTypes[59]
+	ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
+	ms.StoreMessageInfo(mi)
+}
+
+func (x *StringULIDIgnore) String() string {
+	return protoimpl.X.MessageStringOf(x)
+}
+
+func (*StringULIDIgnore) ProtoMessage() {}
+
+func (x *StringULIDIgnore) ProtoReflect() protoreflect.Message {
+	mi := &file_buf_validate_conformance_cases_strings_proto_msgTypes[59]
+	if x != nil {
+		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
+		if ms.LoadMessageInfo() == nil {
+			ms.StoreMessageInfo(mi)
+		}
+		return ms
+	}
+	return mi.MessageOf(x)
+}
+
+// Deprecated: Use StringULIDIgnore.ProtoReflect.Descriptor instead.
+func (*StringULIDIgnore) Descriptor() ([]byte, []int) {
+	return file_buf_validate_conformance_cases_strings_proto_rawDescGZIP(), []int{59}
+}
+
+func (x *StringULIDIgnore) GetVal() string {
+	if x != nil {
+		return x.Val
+	}
+	return ""
+}
+
 type StringInOneof struct {
 	state protoimpl.MessageState `protogen:"open.v1"`
 	// Types that are valid to be assigned to Foo:
@@ -2556,7 +2688,7 @@ type StringInOneof struct {
 
 func (x *StringInOneof) Reset() {
 	*x = StringInOneof{}
-	mi := &file_buf_validate_conformance_cases_strings_proto_msgTypes[57]
+	mi := &file_buf_validate_conformance_cases_strings_proto_msgTypes[60]
 	ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
 	ms.StoreMessageInfo(mi)
 }
@@ -2568,7 +2700,7 @@ func (x *StringInOneof) String() string {
 func (*StringInOneof) ProtoMessage() {}
 
 func (x *StringInOneof) ProtoReflect() protoreflect.Message {
-	mi := &file_buf_validate_conformance_cases_strings_proto_msgTypes[57]
+	mi := &file_buf_validate_conformance_cases_strings_proto_msgTypes[60]
 	if x != nil {
 		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
 		if ms.LoadMessageInfo() == nil {
@@ -2581,7 +2713,7 @@ func (x *StringInOneof) ProtoReflect() protoreflect.Message {
 
 // Deprecated: Use StringInOneof.ProtoReflect.Descriptor instead.
 func (*StringInOneof) Descriptor() ([]byte, []int) {
-	return file_buf_validate_conformance_cases_strings_proto_rawDescGZIP(), []int{57}
+	return file_buf_validate_conformance_cases_strings_proto_rawDescGZIP(), []int{60}
 }
 
 func (x *StringInOneof) GetFoo() isStringInOneof_Foo {
@@ -2619,7 +2751,7 @@ type StringHostAndPort struct {
 
 func (x *StringHostAndPort) Reset() {
 	*x = StringHostAndPort{}
-	mi := &file_buf_validate_conformance_cases_strings_proto_msgTypes[58]
+	mi := &file_buf_validate_conformance_cases_strings_proto_msgTypes[61]
 	ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
 	ms.StoreMessageInfo(mi)
 }
@@ -2631,7 +2763,7 @@ func (x *StringHostAndPort) String() string {
 func (*StringHostAndPort) ProtoMessage() {}
 
 func (x *StringHostAndPort) ProtoReflect() protoreflect.Message {
-	mi := &file_buf_validate_conformance_cases_strings_proto_msgTypes[58]
+	mi := &file_buf_validate_conformance_cases_strings_proto_msgTypes[61]
 	if x != nil {
 		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
 		if ms.LoadMessageInfo() == nil {
@@ -2644,7 +2776,7 @@ func (x *StringHostAndPort) ProtoReflect() protoreflect.Message {
 
 // Deprecated: Use StringHostAndPort.ProtoReflect.Descriptor instead.
 func (*StringHostAndPort) Descriptor() ([]byte, []int) {
-	return file_buf_validate_conformance_cases_strings_proto_rawDescGZIP(), []int{58}
+	return file_buf_validate_conformance_cases_strings_proto_rawDescGZIP(), []int{61}
 }
 
 func (x *StringHostAndPort) GetVal() string {
@@ -2663,7 +2795,7 @@ type StringHostAndOptionalPort struct {
 
 func (x *StringHostAndOptionalPort) Reset() {
 	*x = StringHostAndOptionalPort{}
-	mi := &file_buf_validate_conformance_cases_strings_proto_msgTypes[59]
+	mi := &file_buf_validate_conformance_cases_strings_proto_msgTypes[62]
 	ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
 	ms.StoreMessageInfo(mi)
 }
@@ -2675,7 +2807,7 @@ func (x *StringHostAndOptionalPort) String() string {
 func (*StringHostAndOptionalPort) ProtoMessage() {}
 
 func (x *StringHostAndOptionalPort) ProtoReflect() protoreflect.Message {
-	mi := &file_buf_validate_conformance_cases_strings_proto_msgTypes[59]
+	mi := &file_buf_validate_conformance_cases_strings_proto_msgTypes[62]
 	if x != nil {
 		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
 		if ms.LoadMessageInfo() == nil {
@@ -2688,7 +2820,7 @@ func (x *StringHostAndOptionalPort) ProtoReflect() protoreflect.Message {
 
 // Deprecated: Use StringHostAndOptionalPort.ProtoReflect.Descriptor instead.
 func (*StringHostAndOptionalPort) Descriptor() ([]byte, []int) {
-	return file_buf_validate_conformance_cases_strings_proto_rawDescGZIP(), []int{59}
+	return file_buf_validate_conformance_cases_strings_proto_rawDescGZIP(), []int{62}
 }
 
 func (x *StringHostAndOptionalPort) GetVal() string {
@@ -2707,7 +2839,7 @@ type StringExample struct {
 
 func (x *StringExample) Reset() {
 	*x = StringExample{}
-	mi := &file_buf_validate_conformance_cases_strings_proto_msgTypes[60]
+	mi := &file_buf_validate_conformance_cases_strings_proto_msgTypes[63]
 	ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
 	ms.StoreMessageInfo(mi)
 }
@@ -2719,7 +2851,7 @@ func (x *StringExample) String() string {
 func (*StringExample) ProtoMessage() {}
 
 func (x *StringExample) ProtoReflect() protoreflect.Message {
-	mi := &file_buf_validate_conformance_cases_strings_proto_msgTypes[60]
+	mi := &file_buf_validate_conformance_cases_strings_proto_msgTypes[63]
 	if x != nil {
 		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
 		if ms.LoadMessageInfo() == nil {
@@ -2732,7 +2864,7 @@ func (x *StringExample) ProtoReflect() protoreflect.Message {
 
 // Deprecated: Use StringExample.ProtoReflect.Descriptor instead.
 func (*StringExample) Descriptor() ([]byte, []int) {
-	return file_buf_validate_conformance_cases_strings_proto_rawDescGZIP(), []int{60}
+	return file_buf_validate_conformance_cases_strings_proto_rawDescGZIP(), []int{63}
 }
 
 func (x *StringExample) GetVal() string {
@@ -2861,7 +2993,12 @@ const file_buf_validate_conformance_cases_strings_proto_rawDesc = "" +
 	"\vStringTUUID\x12\x1a\n" +
 	"\x03val\x18\x01 \x01(\tB\b\xbaH\x05r\x03\x88\x02\x01R\x03val\",\n" +
 	"\x0eStringNotTUUID\x12\x1a\n" +
-	"\x03val\x18\x01 \x01(\tB\b\xbaH\x05r\x03\x88\x02\x00R\x03val\"2\n" +
+	"\x03val\x18\x01 \x01(\tB\b\xbaH\x05r\x03\x88\x02\x00R\x03val\"(\n" +
+	"\n" +
+	"StringULID\x12\x1a\n" +
+	"\x03val\x18\x01 \x01(\tB\b\xbaH\x05r\x03\x98\x02\x01R\x03val\"+\n" +
+	"\rStringNotULID\x12\x1a\n" +
+	"\x03val\x18\x01 \x01(\tB\b\xbaH\x05r\x03\x98\x02\x00R\x03val\"2\n" +
 	"\x14StringHttpHeaderName\x12\x1a\n" +
 	"\x03val\x18\x01 \x01(\tB\b\xbaH\x05r\x03\xc0\x01\x01R\x03val\"3\n" +
 	"\x15StringHttpHeaderValue\x12\x1a\n" +
@@ -2871,7 +3008,9 @@ const file_buf_validate_conformance_cases_strings_proto_rawDesc = "" +
 	"\x1aStringHttpHeaderValueLoose\x12\x1d\n" +
 	"\x03val\x18\x01 \x01(\tB\v\xbaH\br\x06\xc8\x01\x00\xc0\x01\x02R\x03val\"1\n" +
 	"\x10StringUUIDIgnore\x12\x1d\n" +
-	"\x03val\x18\x01 \x01(\tB\v\xbaH\b\xd8\x01\x01r\x03\xb0\x01\x01R\x03val\"7\n" +
+	"\x03val\x18\x01 \x01(\tB\v\xbaH\b\xd8\x01\x01r\x03\xb0\x01\x01R\x03val\"1\n" +
+	"\x10StringULIDIgnore\x12\x1d\n" +
+	"\x03val\x18\x01 \x01(\tB\v\xbaH\b\xd8\x01\x01r\x03\x98\x02\x01R\x03val\"7\n" +
 	"\rStringInOneof\x12\x1f\n" +
 	"\x03bar\x18\x01 \x01(\tB\v\xbaH\br\x06R\x01aR\x01bH\x00R\x03barB\x05\n" +
 	"\x03foo\"/\n" +
@@ -2896,7 +3035,7 @@ func file_buf_validate_conformance_cases_strings_proto_rawDescGZIP() []byte {
 	return file_buf_validate_conformance_cases_strings_proto_rawDescData
 }
 
-var file_buf_validate_conformance_cases_strings_proto_msgTypes = make([]protoimpl.MessageInfo, 61)
+var file_buf_validate_conformance_cases_strings_proto_msgTypes = make([]protoimpl.MessageInfo, 64)
 var file_buf_validate_conformance_cases_strings_proto_goTypes = []any{
 	(*StringNone)(nil),                 // 0: buf.validate.conformance.cases.StringNone
 	(*StringConst)(nil),                // 1: buf.validate.conformance.cases.StringConst
@@ -2950,15 +3089,18 @@ var file_buf_validate_conformance_cases_strings_proto_goTypes = []any{
 	(*StringNotUUID)(nil),              // 49: buf.validate.conformance.cases.StringNotUUID
 	(*StringTUUID)(nil),                // 50: buf.validate.conformance.cases.StringTUUID
 	(*StringNotTUUID)(nil),             // 51: buf.validate.conformance.cases.StringNotTUUID
-	(*StringHttpHeaderName)(nil),       // 52: buf.validate.conformance.cases.StringHttpHeaderName
-	(*StringHttpHeaderValue)(nil),      // 53: buf.validate.conformance.cases.StringHttpHeaderValue
-	(*StringHttpHeaderNameLoose)(nil),  // 54: buf.validate.conformance.cases.StringHttpHeaderNameLoose
-	(*StringHttpHeaderValueLoose)(nil), // 55: buf.validate.conformance.cases.StringHttpHeaderValueLoose
-	(*StringUUIDIgnore)(nil),           // 56: buf.validate.conformance.cases.StringUUIDIgnore
-	(*StringInOneof)(nil),              // 57: buf.validate.conformance.cases.StringInOneof
-	(*StringHostAndPort)(nil),          // 58: buf.validate.conformance.cases.StringHostAndPort
-	(*StringHostAndOptionalPort)(nil),  // 59: buf.validate.conformance.cases.StringHostAndOptionalPort
-	(*StringExample)(nil),              // 60: buf.validate.conformance.cases.StringExample
+	(*StringULID)(nil),                 // 52: buf.validate.conformance.cases.StringULID
+	(*StringNotULID)(nil),              // 53: buf.validate.conformance.cases.StringNotULID
+	(*StringHttpHeaderName)(nil),       // 54: buf.validate.conformance.cases.StringHttpHeaderName
+	(*StringHttpHeaderValue)(nil),      // 55: buf.validate.conformance.cases.StringHttpHeaderValue
+	(*StringHttpHeaderNameLoose)(nil),  // 56: buf.validate.conformance.cases.StringHttpHeaderNameLoose
+	(*StringHttpHeaderValueLoose)(nil), // 57: buf.validate.conformance.cases.StringHttpHeaderValueLoose
+	(*StringUUIDIgnore)(nil),           // 58: buf.validate.conformance.cases.StringUUIDIgnore
+	(*StringULIDIgnore)(nil),           // 59: buf.validate.conformance.cases.StringULIDIgnore
+	(*StringInOneof)(nil),              // 60: buf.validate.conformance.cases.StringInOneof
+	(*StringHostAndPort)(nil),          // 61: buf.validate.conformance.cases.StringHostAndPort
+	(*StringHostAndOptionalPort)(nil),  // 62: buf.validate.conformance.cases.StringHostAndOptionalPort
+	(*StringExample)(nil),              // 63: buf.validate.conformance.cases.StringExample
 }
 var file_buf_validate_conformance_cases_strings_proto_depIdxs = []int32{
 	0, // [0:0] is the sub-list for method output_type
@@ -2973,7 +3115,7 @@ func file_buf_validate_conformance_cases_strings_proto_init() {
 	if File_buf_validate_conformance_cases_strings_proto != nil {
 		return
 	}
-	file_buf_validate_conformance_cases_strings_proto_msgTypes[57].OneofWrappers = []any{
+	file_buf_validate_conformance_cases_strings_proto_msgTypes[60].OneofWrappers = []any{
 		(*StringInOneof_Bar)(nil),
 	}
 	type x struct{}
@@ -2982,7 +3124,7 @@ func file_buf_validate_conformance_cases_strings_proto_init() {
 			GoPackagePath: reflect.TypeOf(x{}).PkgPath(),
 			RawDescriptor: unsafe.Slice(unsafe.StringData(file_buf_validate_conformance_cases_strings_proto_rawDesc), len(file_buf_validate_conformance_cases_strings_proto_rawDesc)),
 			NumEnums:      0,
-			NumMessages:   61,
+			NumMessages:   64,
 			NumExtensions: 0,
 			NumServices:   0,
 		},
diff --git a/tools/internal/gen/buf/validate/validate.pb.go b/tools/internal/gen/buf/validate/validate.pb.go
index 9611d098..7e026070 100644
--- a/tools/internal/gen/buf/validate/validate.pb.go
+++ b/tools/internal/gen/buf/validate/validate.pb.go
@@ -4740,6 +4740,7 @@ type StringRules struct {
 	//	*StringRules_Ipv4Prefix
 	//	*StringRules_Ipv6Prefix
 	//	*StringRules_HostAndPort
+	//	*StringRules_Ulid
 	//	*StringRules_WellKnownRegex
 	WellKnown isStringRules_WellKnown `protobuf_oneof:"well_known"`
 	// This applies to regexes `HTTP_HEADER_NAME` and `HTTP_HEADER_VALUE` to
@@ -5065,6 +5066,15 @@ func (x *StringRules) GetHostAndPort() bool {
 	return false
 }
 
+func (x *StringRules) GetUlid() bool {
+	if x != nil {
+		if x, ok := x.WellKnown.(*StringRules_Ulid); ok {
+			return x.Ulid
+		}
+	}
+	return false
+}
+
 func (x *StringRules) GetWellKnownRegex() KnownRegex {
 	if x != nil {
 		if x, ok := x.WellKnown.(*StringRules_WellKnownRegex); ok {
@@ -5419,6 +5429,24 @@ type StringRules_HostAndPort struct {
 	HostAndPort bool `protobuf:"varint,32,opt,name=host_and_port,json=hostAndPort,oneof"`
 }
 
+type StringRules_Ulid struct {
+	// `ulid` specifies that the field value must be a valid ULID (Universally Unique
+	// Lexicographically Sortable Identifier) as defined by the [ULID specification](https://github.com/ulid/spec).
+	// ULID is a 26-character Base32-encoded string using Crockford's Base32 alphabet
+	// (0-9, A-Z excluding I, L, O, U). If the field value isn't a valid ULID, an error
+	// message will be generated.
+	//
+	// ```proto
+	//
+	//	message MyString {
+	//	  // value must be a valid ULID
+	//	  string value = 1 [(buf.validate.field).string.ulid = true];
+	//	}
+	//
+	// ```
+	Ulid bool `protobuf:"varint,35,opt,name=ulid,oneof"`
+}
+
 type StringRules_WellKnownRegex struct {
 	// `well_known_regex` specifies a common well-known pattern
 	// defined as a regex. If the field value doesn't match the well-known
@@ -5479,6 +5507,8 @@ func (*StringRules_Ipv6Prefix) isStringRules_WellKnown() {}
 
 func (*StringRules_HostAndPort) isStringRules_WellKnown() {}
 
+func (*StringRules_Ulid) isStringRules_WellKnown() {}
+
 func (*StringRules_WellKnownRegex) isStringRules_WellKnown() {}
 
 // BytesRules describe the rules applied to `bytes` values. These rules
@@ -8079,7 +8109,7 @@ const file_buf_validate_validate_proto_rawDesc = "" +
 	"bool.const\x1a`this != getField(rules, 'const') ? 'value must equal %s'.format([getField(rules, 'const')]) : ''R\x05const\x123\n" +
 	"\aexample\x18\x02 \x03(\bB\x19\xc2H\x16\n" +
 	"\x14\n" +
-	"\fbool.example\x1a\x04trueR\aexample*\t\b\xe8\a\x10\x80\x80\x80\x80\x02\"\xd19\n" +
+	"\fbool.example\x1a\x04trueR\aexample*\t\b\xe8\a\x10\x80\x80\x80\x80\x02\"\xc9;\n" +
 	"\vStringRules\x12\x8d\x01\n" +
 	"\x05const\x18\x01 \x01(\tBw\xc2Ht\n" +
 	"r\n" +
@@ -8210,7 +8240,12 @@ const file_buf_validate_validate_proto_rawDesc = "" +
 	"\x99\x01\n" +
 	"\x14string.host_and_port\x12Avalue must be a valid host (hostname or IP address) and port pair\x1a>!rules.host_and_port || this == '' || this.isHostAndPort(true)\n" +
 	"y\n" +
-	"\x1astring.host_and_port_empty\x127value is empty, which is not a valid host and port pair\x1a\"!rules.host_and_port || this != ''H\x00R\vhostAndPort\x12\xb8\x05\n" +
+	"\x1astring.host_and_port_empty\x127value is empty, which is not a valid host and port pair\x1a\"!rules.host_and_port || this != ''H\x00R\vhostAndPort\x12\xf5\x01\n" +
+	"\x04ulid\x18# \x01(\bB\xde\x01\xc2H\xda\x01\n" +
+	"}\n" +
+	"\vstring.ulid\x12\x1avalue must be a valid ULID\x1aR!rules.ulid || this == '' || this.matches('^[0-9A-HJKMNP-TV-Za-hjkmnp-tv-z]{26}$')\n" +
+	"Y\n" +
+	"\x11string.ulid_empty\x12)value is empty, which is not a valid ULID\x1a\x19!rules.ulid || this != ''H\x00R\x04ulid\x12\xb8\x05\n" +
 	"\x10well_known_regex\x18\x18 \x01(\x0e2\x18.buf.validate.KnownRegexB\xf1\x04\xc2H\xed\x04\n" +
 	"\xf0\x01\n" +
 	"#string.well_known_regex.header_name\x12&value must be a valid HTTP header name\x1a\xa0\x01rules.well_known_regex != 1 || this == '' || this.matches(!has(rules.strict) || rules.strict ?'^:?[0-9a-zA-Z!#$%&\\'*+-.^_|~\\x60]+$' :'^[^\\u0000\\u000A\\u000D]+$')\n" +
@@ -8696,6 +8731,7 @@ func file_buf_validate_validate_proto_init() {
 		(*StringRules_Ipv4Prefix)(nil),
 		(*StringRules_Ipv6Prefix)(nil),
 		(*StringRules_HostAndPort)(nil),
+		(*StringRules_Ulid)(nil),
 		(*StringRules_WellKnownRegex)(nil),
 	}
 	file_buf_validate_validate_proto_msgTypes[20].OneofWrappers = []any{
diff --git a/tools/protovalidate-conformance/internal/cases/cases_strings.go b/tools/protovalidate-conformance/internal/cases/cases_strings.go
index 5a1418f2..3c242ec6 100644
--- a/tools/protovalidate-conformance/internal/cases/cases_strings.go
+++ b/tools/protovalidate-conformance/internal/cases/cases_strings.go
@@ -1402,6 +1402,110 @@ func stringSuite() suites.Suite {
 				},
 			),
 		},
+		"ulid/valid/lowercase": {
+			Message:  &cases.StringULID{Val: "01arz3ndektsv4rrffq69g5fav"},
+			Expected: results.Success(true),
+		},
+		"ulid/valid/uppercase": {
+			Message:  &cases.StringULID{Val: "01ARZ3NDEKTSV4RRFFQ69G5FAV"},
+			Expected: results.Success(true),
+		},
+		"ulid/valid/mixed_case": {
+			Message:  &cases.StringULID{Val: "01ArZ3NdEkTsV4RrFfQ69G5FaV"},
+			Expected: results.Success(true),
+		},
+		"ulid/valid/nil": {
+			Message:  &cases.StringULID{Val: "00000000000000000000000000"},
+			Expected: results.Success(true),
+		},
+		"ulid/invalid/empty": {
+			Message: &cases.StringULID{Val: ""},
+			Expected: results.Violations(
+				&validate.Violation{
+					Field:  results.FieldPath("val"),
+					Rule:   results.FieldPath("string.ulid"),
+					RuleId: proto.String("string.ulid_empty"),
+				},
+			),
+		},
+		"ulid/invalid/not_checked/empty": {
+			Message:  &cases.StringNotULID{Val: ""},
+			Expected: results.Success(true),
+		},
+		"ulid/invalid/not_checked/malformed": {
+			Message:  &cases.StringNotULID{Val: "foobar"},
+			Expected: results.Success(true),
+		},
+		"ulid/invalid/malformed": {
+			Message: &cases.StringULID{Val: "foobar"},
+			Expected: results.Violations(
+				&validate.Violation{
+					Field:  results.FieldPath("val"),
+					Rule:   results.FieldPath("string.ulid"),
+					RuleId: proto.String("string.ulid"),
+				},
+			),
+		},
+		"ulid/invalid/too_short": {
+			Message: &cases.StringULID{Val: "01ARZ3NDEKTSV4RRFFQ69G5FA"},
+			Expected: results.Violations(
+				&validate.Violation{
+					Field:  results.FieldPath("val"),
+					Rule:   results.FieldPath("string.ulid"),
+					RuleId: proto.String("string.ulid"),
+				},
+			),
+		},
+		"ulid/invalid/too_long": {
+			Message: &cases.StringULID{Val: "01ARZ3NDEKTSV4RRFFQ69G5FAVX"},
+			Expected: results.Violations(
+				&validate.Violation{
+					Field:  results.FieldPath("val"),
+					Rule:   results.FieldPath("string.ulid"),
+					RuleId: proto.String("string.ulid"),
+				},
+			),
+		},
+		"ulid/invalid/invalid_characters/i": {
+			Message: &cases.StringULID{Val: "01ARZ3NDEKTSV4RRFFQ69G5FAI"},
+			Expected: results.Violations(
+				&validate.Violation{
+					Field:  results.FieldPath("val"),
+					Rule:   results.FieldPath("string.ulid"),
+					RuleId: proto.String("string.ulid"),
+				},
+			),
+		},
+		"ulid/invalid/invalid_characters/l": {
+			Message: &cases.StringULID{Val: "01ARZ3NDEKTSV4RRFFQ69G5FAL"},
+			Expected: results.Violations(
+				&validate.Violation{
+					Field:  results.FieldPath("val"),
+					Rule:   results.FieldPath("string.ulid"),
+					RuleId: proto.String("string.ulid"),
+				},
+			),
+		},
+		"ulid/invalid/invalid_characters/o": {
+			Message: &cases.StringULID{Val: "01ARZ3NDEKTSV4RRFFQ69G5FAO"},
+			Expected: results.Violations(
+				&validate.Violation{
+					Field:  results.FieldPath("val"),
+					Rule:   results.FieldPath("string.ulid"),
+					RuleId: proto.String("string.ulid"),
+				},
+			),
+		},
+		"ulid/invalid/invalid_characters/u": {
+			Message: &cases.StringULID{Val: "01ARZ3NDEKTSV4RRFFQ69G5FAU"},
+			Expected: results.Violations(
+				&validate.Violation{
+					Field:  results.FieldPath("val"),
+					Rule:   results.FieldPath("string.ulid"),
+					RuleId: proto.String("string.ulid"),
+				},
+			),
+		},
 		"well_known_regex/header_name/strict/valid/header": {
 			Message:  &cases.StringHttpHeaderName{Val: "clustername"},
 			Expected: results.Success(true),