diff --git a/error.go b/error.go
new file mode 100644
index 0000000..127ab45
--- /dev/null
+++ b/error.go
@@ -0,0 +1,97 @@
+package mstdn
+
+import (
+	"encoding/json"
+	"fmt"
+	"io"
+	"net/http"
+
+	"sourcecode.social/reiver/go-opt"
+)
+
+func errorJSON(writer io.Writer, statusCode int, msg ...interface{}) {
+	if nil == writer {
+		return
+	}
+
+	// short error message.
+	var short string
+	{
+		var shortErrorMessage opt.Optional[string]
+
+		shortErrorMessage.WhenNothing(func(){
+			if 1 <= len(msg) {
+				shortErrorMessage = opt.Something(fmt.Sprint(msg[0]))
+			}
+		})
+		shortErrorMessage.WhenNothing(func(){
+			shortErrorMessage = opt.Something(http.StatusText(statusCode))
+		})
+
+		shortErrorMessage.WhenSomething(func(value string){
+			short = value
+		})
+	}
+
+
+	var long opt.Optional[string]
+	{
+		if 2 <= len(msg) {
+			long = opt.Something(fmt.Sprint(msg[1:]...))
+		}
+	}
+
+	var array [512]byte
+	var buffer []byte = array[:0]
+	{
+
+		buffer = append(buffer, "{"...)
+			buffer = append(buffer, `"error":`...)
+			{
+				// This should never return an error since we are passing a string.
+				marshaled, _ := json.Marshal(short)
+
+				buffer = append(buffer, marshaled...)
+			}
+
+			long.WhenSomething(func(value string){
+				buffer = append(buffer, `,"error_description":`...)
+
+				// This should never return an error since we are passing a string.
+				marshaled, _ := json.Marshal(value)
+
+				buffer = append(buffer, marshaled...)
+			})
+		buffer = append(buffer, "}"...)
+	}
+
+	writer.Write(buffer)
+}
+
+// Error responds to the request with the specified error message and HTTP code.
+// The response will be in JSON (application/json; charset=utf-8).
+//
+// For example:
+//
+//	var statusCode int = http.StatusUnauthorized
+//	var shortErrorMessage = http.StatusText(http.StatusUnauthorized)
+//	var longErrorMessage = "Access Denied!!! — you can keep on knocking but you can't come in"
+//	
+//	mstdn.Error(resp, statusCode, shortErrorMessage, longErrorMessage)
+//
+// Responds with:
+//
+//	{
+//		"error":"Unauthorized",
+//		"error_description":"Access Defined!!!! — you can keep on knocking but you can't come in"
+//	}
+func Error(resp http.ResponseWriter, statusCode int, msg ...interface{}) {
+	if nil == resp {
+		return
+	}
+
+	resp.WriteHeader(statusCode)
+	resp.Header().Add("Content-Type", "application/json; charset=utf-8")
+
+	errorJSON(resp, statusCode, msg...)
+}
diff --git a/errorjson_test.go b/errorjson_test.go
new file mode 100644
index 0000000..57f77aa
--- /dev/null
+++ b/errorjson_test.go
@@ -0,0 +1,203 @@
+package mstdn
+
+import (
+	"testing"
+
+	"strings"
+)
+
+func TestErrorJSON(t *testing.T) {
+
+	tests := []struct{
+		StatusCode int
+		Message []interface{}
+		Expected string
+	}{
+		{
+			StatusCode: 400,
+			Message: []interface{}{},
+			Expected: `{"error":"Bad Request"}`,
+		},
+		{
+			StatusCode: 401,
+			Message: []interface{}{},
+			Expected: `{"error":"Unauthorized"}`,
+		},
+		{
+			StatusCode: 403,
+			Message: []interface{}{},
+			Expected: `{"error":"Forbidden"}`,
+		},
+		{
+			StatusCode: 404,
+			Message: []interface{}{},
+			Expected: `{"error":"Not Found"}`,
+		},
+		{
+			StatusCode: 422,
+			Message: []interface{}{},
+			Expected: `{"error":"Unprocessable Entity"}`,
+		},
+		{
+			StatusCode: 429,
+			Message: []interface{}{},
+			Expected: `{"error":"Too Many Requests"}`,
+		},
+		{
+			StatusCode: 500,
+			Message: []interface{}{},
+			Expected: `{"error":"Internal Server Error"}`,
+		},
+		{
+			StatusCode: 503,
+			Message: []interface{}{},
+			Expected: `{"error":"Service Unavailable"}`,
+		},
+
+
+
+		{
+			StatusCode: 400,
+			Message: []interface{}{"very bad request"},
+			Expected: `{"error":"very bad request"}`,
+		},
+		{
+			StatusCode: 401,
+			Message: []interface{}{"get out of here"},
+			Expected: `{"error":"get out of here"}`,
+		},
+		{
+			StatusCode: 403,
+			Message: []interface{}{"no!!!!"},
+			Expected: `{"error":"no!!!!"}`,
+		},
+		{
+			StatusCode: 404,
+			Message: []interface{}{"huh?"},
+			Expected: `{"error":"huh?"}`,
+		},
+		{
+			StatusCode: 422,
+			Message: []interface{}{"WTF?"},
+			Expected: `{"error":"WTF?"}`,
+		},
+		{
+			StatusCode: 429,
+			Message: []interface{}{"f-off"},
+			Expected: `{"error":"f-off"}`,
+		},
+		{
+			StatusCode: 500,
+			Message: []interface{}{"crap!"},
+			Expected: `{"error":"crap!"}`,
+		},
+		{
+			StatusCode: 503,
+			Message: []interface{}{"nope"},
+			Expected: `{"error":"nope"}`,
+		},
+
+
+
+		{
+			StatusCode: 400,
+			Message: []interface{}{"very bad request", "you have been naughty"},
+			Expected: `{"error":"very bad request","error_description":"you have been naughty"}`,
+		},
+		{
+			StatusCode: 401,
+			Message: []interface{}{"get out of here", "access denied!!! — you can keep on knocking but you can't come in"},
+			Expected: `{"error":"get out of here","error_description":"access denied!!! — you can keep on knocking but you can't come in"}`,
+		},
+		{
+			StatusCode: 403,
+			Message: []interface{}{"no!!!!", "go away"},
+			Expected: `{"error":"no!!!!","error_description":"go away"}`,
+		},
+		{
+			StatusCode: 404,
+			Message: []interface{}{"huh?", "what are you talking about"},
+			Expected: `{"error":"huh?","error_description":"what are you talking about"}`,
+		},
+		{
+			StatusCode: 422,
+			Message: []interface{}{"WTF?", "i don't understand the words coming out of your mouth"},
+			Expected: `{"error":"WTF?","error_description":"i don't understand the words coming out of your mouth"}`,
+		},
+		{
+			StatusCode: 429,
+			Message: []interface{}{"f-off", "slow it down, back it up"},
+			Expected: `{"error":"f-off","error_description":"slow it down, back it up"}`,
+		},
+		{
+			StatusCode: 500,
+			Message: []interface{}{"crap!", "i f-ed up"},
+			Expected: `{"error":"crap!","error_description":"i f-ed up"}`,
+		},
+		{
+			StatusCode: 503,
+			Message: []interface{}{"nope", "it not workie"},
+			Expected: `{"error":"nope","error_description":"it not workie"}`,
+		},
+
+
+
+		{
+			StatusCode: 400,
+			Message: []interface{}{"very bad request", "you have been naughty", " :-)"},
+			Expected: `{"error":"very bad request","error_description":"you have been naughty :-)"}`,
+		},
+		{
+			StatusCode: 401,
+			Message: []interface{}{"get out of here", "access denied!!! — you can keep on knocking but you can't come in", "."},
+			Expected: `{"error":"get out of here","error_description":"access denied!!! — you can keep on knocking but you can't come in."}`,
+		},
+		{
+			StatusCode: 403,
+			Message: []interface{}{"no!!!!", "go away", "!"},
+			Expected: `{"error":"no!!!!","error_description":"go away!"}`,
+		},
+		{
+			StatusCode: 404,
+			Message: []interface{}{"huh?", "what are you talking about", "?"},
+			Expected: `{"error":"huh?","error_description":"what are you talking about?"}`,
+		},
+		{
+			StatusCode: 422,
+			Message: []interface{}{"WTF?", "i don't understand the words coming out of your mouth", "."},
+			Expected: `{"error":"WTF?","error_description":"i don't understand the words coming out of your mouth."}`,
+		},
+		{
+			StatusCode: 429,
+			Message: []interface{}{"f-off", "slow it down, back it up", "."},
+			Expected: `{"error":"f-off","error_description":"slow it down, back it up."}`,
+		},
+		{
+			StatusCode: 500,
+			Message: []interface{}{"crap!", "i f-ed up", " :-("},
+			Expected: `{"error":"crap!","error_description":"i f-ed up :-("}`,
+		},
+		{
+			StatusCode: 503,
+			Message: []interface{}{"nope", "it not workie", "."},
+			Expected: `{"error":"nope","error_description":"it not workie."}`,
+		},
+	}
+
+	for testNumber, test := range tests {
+
+		var actualBuffer strings.Builder
+
+		errorJSON(&actualBuffer, test.StatusCode, test.Message...)
+
+		actual := actualBuffer.String()
+		expected := test.Expected
+
+		if expected != actual {
+			t.Errorf("For test #%d, the actual value is not what was expected.", testNumber)
+			t.Logf("EXPECTED:\n%s", expected)
+			t.Logf("ACTUAL:\n%s", actual)
+			continue
+		}
+	}
+}