diff --git a/README.md b/README.md
index cab0f9f..4108deb 100644
--- a/README.md
+++ b/README.md
@@ -193,11 +193,15 @@ we'll get `children` array and reverse the order:
 "children|@reverse|0"         >> "Jack"
 ```
 
-There are currently three built-in modifiers:
+There are currently the following built-in modifiers:
 
 - `@reverse`: Reverse an array or the members of an object.
 - `@ugly`: Remove all whitespace from a json document.
 - `@pretty`: Make the json document more human readable.
+- `@this`: Returns the current element. It can be used to retrieve the root element.
+- `@valid`: Ensure the json document is valid.
+- `@flatten`: Flattens an array.
+- `@join`: Joins multiple objects into a single object.
 
 ### Modifier arguments
 
diff --git a/SYNTAX.md b/SYNTAX.md
index ed584de..9558019 100644
--- a/SYNTAX.md
+++ b/SYNTAX.md
@@ -181,12 +181,15 @@ children.@reverse                   ["Jack","Alex","Sara"]
 children.@reverse.0                 "Jack"
 ```
 
-There are currently three built-in modifiers:
+There are currently the following built-in modifiers:
 
 - `@reverse`: Reverse an array or the members of an object.
 - `@ugly`: Remove all whitespace from JSON.
 - `@pretty`: Make the JSON more human readable.
-- `@this`: Returns the current element. Can be used to retrieve the root element.
+- `@this`: Returns the current element. It can be used to retrieve the root element.
+- `@valid`: Ensure the json document is valid.
+- `@flatten`: Flattens an array.
+- `@join`: Joins multiple objects into a single object.
 
 #### Modifier arguments
 
diff --git a/gjson.go b/gjson.go
index bac29a9..647ed73 100644
--- a/gjson.go
+++ b/gjson.go
@@ -2595,6 +2595,15 @@ func execModifier(json, path string) (pathOut, res string, ok bool) {
 	return pathOut, res, false
 }
 
+// unwrap removes the '[]' or '{}' characters around json
+func unwrap(json string) string {
+	json = trim(json)
+	if len(json) >= 2 && json[0] == '[' || json[0] == '{' {
+		json = json[1 : len(json)-1]
+	}
+	return json
+}
+
 // DisableModifiers will disable the modifier syntax
 var DisableModifiers = false
 
@@ -2603,6 +2612,9 @@ var modifiers = map[string]func(json, arg string) string{
 	"ugly":    modUgly,
 	"reverse": modReverse,
 	"this":    modThis,
+	"flatten": modFlatten,
+	"join":    modJoin,
+	"valid":   modValid,
 }
 
 // AddModifier binds a custom modifier command to the GJSON syntax.
@@ -2691,3 +2703,122 @@ func modReverse(json, arg string) string {
 	}
 	return json
 }
+
+// @flatten an array with child arrays.
+//   [1,[2],[3,4],[5,[6,7]]] -> [1,2,3,4,5,[6,7]]
+// The {"deep":true} arg can be provide for deep flattening.
+//   [1,[2],[3,4],[5,[6,7]]] -> [1,2,3,4,5,6,7]
+// The original json is returned when the json is not an array.
+func modFlatten(json, arg string) string {
+	res := Parse(json)
+	if !res.IsArray() {
+		return json
+	}
+	var deep bool
+	if arg != "" {
+		Parse(arg).ForEach(func(key, value Result) bool {
+			if key.String() == "deep" {
+				deep = value.Bool()
+			}
+			return true
+		})
+	}
+	var out []byte
+	out = append(out, '[')
+	var idx int
+	res.ForEach(func(_, value Result) bool {
+		if idx > 0 {
+			out = append(out, ',')
+		}
+		if value.IsArray() {
+			if deep {
+				out = append(out, unwrap(modFlatten(value.Raw, arg))...)
+			} else {
+				out = append(out, unwrap(value.Raw)...)
+			}
+		} else {
+			out = append(out, value.Raw...)
+		}
+		idx++
+		return true
+	})
+	out = append(out, ']')
+	return bytesString(out)
+}
+
+// @join multiple objects into a single object.
+//   [{"first":"Tom"},{"last":"Smith"}] -> {"first","Tom","last":"Smith"}
+// The arg can be "true" to specify that duplicate keys should be preserved.
+//   [{"first":"Tom","age":37},{"age":41}] -> {"first","Tom","age":37,"age":41}
+// Without preserved keys:
+//   [{"first":"Tom","age":37},{"age":41}] -> {"first","Tom","age":41}
+// The original json is returned when the json is not an object.
+func modJoin(json, arg string) string {
+	res := Parse(json)
+	if !res.IsArray() {
+		return json
+	}
+	var preserve bool
+	if arg != "" {
+		Parse(arg).ForEach(func(key, value Result) bool {
+			if key.String() == "preserve" {
+				preserve = value.Bool()
+			}
+			return true
+		})
+	}
+	var out []byte
+	out = append(out, '{')
+	if preserve {
+		// Preserve duplicate keys.
+		var idx int
+		res.ForEach(func(_, value Result) bool {
+			if !value.IsObject() {
+				return true
+			}
+			if idx > 0 {
+				out = append(out, ',')
+			}
+			out = append(out, unwrap(value.Raw)...)
+			idx++
+			return true
+		})
+	} else {
+		// Deduplicate keys and generate an object with stable ordering.
+		var keys []Result
+		kvals := make(map[string]Result)
+		res.ForEach(func(_, value Result) bool {
+			if !value.IsObject() {
+				return true
+			}
+			value.ForEach(func(key, value Result) bool {
+				k := key.String()
+				if _, ok := kvals[k]; !ok {
+					keys = append(keys, key)
+				}
+				kvals[k] = value
+				return true
+			})
+			return true
+		})
+		for i := 0; i < len(keys); i++ {
+			if i > 0 {
+				out = append(out, ',')
+			}
+			out = append(out, keys[i].Raw...)
+			out = append(out, ':')
+			out = append(out, kvals[keys[i].String()].Raw...)
+		}
+	}
+	out = append(out, '}')
+	return bytesString(out)
+}
+
+// @valid ensures that the json is valid before moving on. An empty string is
+// returned when the json is not valid, otherwise it returns the original json.
+func modValid(json, arg string) string {
+	if !Valid(json) {
+		return ""
+	}
+	return json
+}
diff --git a/gjson_test.go b/gjson_test.go
index 7a3255a..36a4273 100644
--- a/gjson_test.go
+++ b/gjson_test.go
@@ -2025,3 +2025,140 @@ func TestChainedModifierStringArgs(t *testing.T) {
 	res := Get("[]", `@push:"2"|@push:"3"|@push:{"a":"b","c":["e","f"]}|@push:true|@push:10.23`)
 	assert(t, res.String() == `["2","3",{"a":"b","c":["e","f"]},true,10.23]`)
 }
+
+func TestFlatten(t *testing.T) {
+	json := `[1,[2],[3,4],[5,[6,[7]]],{"hi":"there"},8,[9]]`
+	assert(t, Get(json, "@flatten").String() == `[1,2,3,4,5,[6,[7]],{"hi":"there"},8,9]`)
+	assert(t, Get(json, `@flatten:{"deep":true}`).String() == `[1,2,3,4,5,6,7,{"hi":"there"},8,9]`)
+	assert(t, Get(`{"9999":1234}`, "@flatten").String() == `{"9999":1234}`)
+}
+
+func TestJoin(t *testing.T) {
+	assert(t, Get(`[{},{}]`, "@join").String() == `{}`)
+	assert(t, Get(`[{"a":1},{"b":2}]`, "@join").String() == `{"a":1,"b":2}`)
+	assert(t, Get(`[{"a":1,"b":1},{"b":2}]`, "@join").String() == `{"a":1,"b":2}`)
+	assert(t, Get(`[{"a":1,"b":1},{"b":2},5,{"c":3}]`, "@join").String() == `{"a":1,"b":2,"c":3}`)
+	assert(t, Get(`[{"a":1,"b":1},{"b":2},5,{"c":3}]`, `@join:{"preserve":true}`).String() == `{"a":1,"b":1,"b":2,"c":3}`)
+	assert(t, Get(`[{"a":1,"b":1},{"b":2},5,{"c":3}]`, `@join:{"preserve":true}.b`).String() == `1`)
+	assert(t, Get(`{"9999":1234}`, "@join").String() == `{"9999":1234}`)
+}
+
+func TestValid(t *testing.T) {
+	assert(t, Get("[{}", "@valid").Exists() == false)
+	assert(t, Get("[{}]", "@valid").Exists() == true)
+}
+
+// https://github.com/tidwall/gjson/issues/152
+func TestJoin152(t *testing.T) {
+	var json = `{
+		"distance": 1374.0,
+		"validFrom": "2005-11-14",
+		"historical": {
+		  "type": "Day",
+		  "name": "last25Hours",
+		  "summary": {
+			"units": {
+			  "temperature": "C",
+			  "wind": "m/s",
+			  "snow": "cm",
+			  "precipitation": "mm"
+			},
+			"days": [
+			  {
+				"time": "2020-02-08",
+				"hours": [
+				  {
+					"temperature": {
+					  "min": -2.0,
+					  "max": -1.6,
+					  "value": -1.6
+					},
+					"wind": {},
+					"precipitation": {},
+					"humidity": {
+					  "value": 92.0
+					},
+					"snow": {
+					  "depth": 49.0
+					},
+					"time": "2020-02-08T16:00:00+01:00"
+				  },
+				  {
+					"temperature": {
+					  "min": -1.7,
+					  "max": -1.3,
+					  "value": -1.3
+					},
+					"wind": {},
+					"precipitation": {},
+					"humidity": {
+					  "value": 92.0
+					},
+					"snow": {
+					  "depth": 49.0
+					},
+					"time": "2020-02-08T17:00:00+01:00"
+				  },
+				  {
+					"temperature": {
+					  "min": -1.3,
+					  "max": -0.9,
+					  "value": -1.2
+					},
+					"wind": {},
+					"precipitation": {},
+					"humidity": {
+					  "value": 91.0
+					},
+					"snow": {
+					  "depth": 49.0
+					},
+					"time": "2020-02-08T18:00:00+01:00"
+				  }
+				]
+			  },
+			  {
+				"time": "2020-02-09",
+				"hours": [
+				  {
+					"temperature": {
+					  "min": -1.7,
+					  "max": -0.9,
+					  "value": -1.5
+					},
+					"wind": {},
+					"precipitation": {},
+					"humidity": {
+					  "value": 91.0
+					},
+					"snow": {
+					  "depth": 49.0
+					},
+					"time": "2020-02-09T00:00:00+01:00"
+				  },
+				  {
+					"temperature": {
+					  "min": -1.5,
+					  "max": 0.9,
+					  "value": 0.2
+					},
+					"wind": {},
+					"precipitation": {},
+					"humidity": {
+					  "value": 67.0
+					},
+					"snow": {
+					  "depth": 49.0
+					},
+					"time": "2020-02-09T01:00:00+01:00"
+				  }
+				]
+			  }
+			]
+		  }
+		}
+	  }`
+
+	res := Get(json, "historical.summary.days.#.hours|@flatten|#.humidity.value")
+	assert(t, res.Raw == `[92.0,92.0,91.0,91.0,67.0]`)
+}