diff --git a/.gitignore b/.gitignore
index 5ea5ffa..67563dc 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,3 +1,4 @@
 *.dSYM
 fsm
 fsm2
+fsm3
diff --git a/fsm3.c b/fsm3.c
new file mode 100644
index 0000000..27c1786
--- /dev/null
+++ b/fsm3.c
@@ -0,0 +1,110 @@
+#include <ctype.h>
+#include <stdbool.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+#define ARR_LEN(X) (sizeof(X) / sizeof(X[0]))
+
+typedef enum {
+  STATE_START,
+  STATE_INVALID,
+  STATE_KEY,
+  STATE_STRING,
+  STATE_KEY_END,
+  STATE_END,
+} states;
+
+typedef states (*state_handler)(char input);
+
+states handle_start(char input);
+states handle_key(char input);
+states handle_string(char input);
+states handle_key_end(char input);
+
+states state_machine(states current, char input);
+
+bool check_input(const char *text);
+
+// clang-format off
+const char *inputs[] = {
+	"",
+	"{\"kjehu efhkwejhf wkehjf iyg\"}",
+	"{",
+	"}",
+	"{\"lkhefhkjhefhjjrj}",
+	"{jhejhuef hkwehj fwe}",
+	"{'wuy iygef'}",
+	"{\"hwekhewf'}",
+};
+// clang-format on
+
+int main(int argc, char *argv[]) {
+  for (int i = 0; i < ARR_LEN(inputs); ++i) {
+    printf("%32s is %s\n", inputs[i],
+           check_input(inputs[i]) ? "VALID" : "INVALID");
+  }
+
+  return EXIT_SUCCESS;
+}
+
+bool check_input(const char *text) {
+  states current = STATE_START;
+
+  for (const char *c = &(text[0]); *c != '\0'; ++c) {
+    current = state_machine(current, *c);
+  }
+
+  return current == STATE_END;
+}
+
+states state_machine(states current, char input) {
+  switch (current) {
+  case STATE_START:
+    return handle_start(input);
+  case STATE_KEY:
+    return handle_key(input);
+  case STATE_STRING:
+    return handle_string(input);
+  case STATE_KEY_END:
+    return handle_key_end(input);
+  case STATE_INVALID:
+  case STATE_END:
+    return current;
+  }
+}
+
+states handle_start(char input) {
+  if (isspace(input)) {
+    return STATE_START;
+  } else if (input == '{') {
+    return STATE_KEY;
+  }
+
+  return STATE_INVALID;
+}
+
+states handle_key(char input) {
+  if (isspace(input)) {
+    return STATE_KEY;
+  } else if (input == '"') {
+    return STATE_STRING;
+  }
+
+  return STATE_INVALID;
+}
+
+states handle_string(char input) {
+  if (input == '"') {
+    return STATE_KEY_END;
+  }
+
+  return STATE_STRING;
+}
+
+states handle_key_end(char input) {
+  if (input == '}') {
+    return STATE_END;
+  }
+
+  return STATE_INVALID;
+}