diff --git a/runtimes/c/include/ads_helpers.h b/runtimes/c/include/ads_helpers.h
index c71f3bb..edad682 100644
--- a/runtimes/c/include/ads_helpers.h
+++ b/runtimes/c/include/ads_helpers.h
@@ -60,6 +60,9 @@ uint32_t ads_bitslice(uint32_t byte, uint8_t bit_start, uint8_t bit_end);
 uint32_t ads_concat_bits(const uint32_t *values, size_t count);
 
 /* ─── Formatter helpers (push items onto result.formatted.items) ──────── */
+/* Every ads_fmt_* takes ownership of the ads_value_t pointers passed in and
+ * frees them (matches ads_result_raw_set's transfer semantics). Pass NULL
+ * to no-op (matches the TS pattern of guarding before calling). */
 
 void ads_fmt_position(ads_decode_result_t *r, ads_value_t *lat, ads_value_t *lon);
 void ads_fmt_position_value(ads_decode_result_t *r, ads_value_t *position);
@@ -75,6 +78,69 @@ void ads_fmt_arrival_airport(ads_decode_result_t *r, ads_value_t *v);
 void ads_fmt_fuel(ads_decode_result_t *r, ads_value_t *v);
 void ads_fmt_unknown_arr(ads_decode_result_t *r, const char *const *values, size_t count);
 
+/* Time-of-day formatters (value in seconds since midnight). */
+void ads_fmt_eta(ads_decode_result_t *r, ads_value_t *v);
+void ads_fmt_off(ads_decode_result_t *r, ads_value_t *v);
+void ads_fmt_on(ads_decode_result_t *r, ads_value_t *v);
+void ads_fmt_in(ads_decode_result_t *r, ads_value_t *v);
+void ads_fmt_out(ads_decode_result_t *r, ads_value_t *v);
+
+/* Calendar formatters. */
+void ads_fmt_day(ads_decode_result_t *r, ads_value_t *v);
+void ads_fmt_departure_day(ads_decode_result_t *r, ads_value_t *v);
+void ads_fmt_arrival_day(ads_decode_result_t *r, ads_value_t *v);
+void ads_fmt_month(ads_decode_result_t *r, ads_value_t *v);
+
+/* Velocity / atmosphere formatters. */
+void ads_fmt_mach(ads_decode_result_t *r, ads_value_t *v);
+void ads_fmt_groundspeed(ads_decode_result_t *r, ads_value_t *v);
+void ads_fmt_airspeed(ads_decode_result_t *r, ads_value_t *v);
+void ads_fmt_temperature(ads_decode_result_t *r, ads_value_t *v);
+void ads_fmt_total_air_temp(ads_decode_result_t *r, ads_value_t *v);
+
+/* Fuel formatters. */
+void ads_fmt_current_fuel(ads_decode_result_t *r, ads_value_t *v);
+void ads_fmt_remaining_fuel(ads_decode_result_t *r, ads_value_t *v);
+
+/* Routing formatters. */
+void ads_fmt_alternate_airport(ads_decode_result_t *r, ads_value_t *v);
+void ads_fmt_arrival_runway(ads_decode_result_t *r, ads_value_t *v);
+void ads_fmt_alternate_runway(ads_decode_result_t *r, ads_value_t *v);
+
+/* Event formatters. */
+void ads_fmt_state_change(ads_decode_result_t *r, const char *from, const char *to);
+void ads_fmt_door_event(ads_decode_result_t *r, const char *door, const char *state);
+
+/* Free-text formatters. */
+void ads_fmt_text(ads_decode_result_t *r, const char *value);
+void ads_fmt_unknown(ads_decode_result_t *r, const char *value);
+void ads_fmt_unknown_sep(ads_decode_result_t *r, const char *value, const char *sep);
+void ads_fmt_unknown_arr_sep(ads_decode_result_t *r, const char *const *values, size_t count, const char *sep);
+
+/* Diagnostic formatters. */
+void ads_fmt_checksum(ads_decode_result_t *r, ads_value_t *v);
+void ads_fmt_checksum_algorithm(ads_decode_result_t *r, const char *value);
+
+/* Generic structured-item push for plugins that emit custom item shapes
+ * (OHMA, WRN, SQ, ATIS, etc.). Stores no raw field; just pushes the item. */
+void ads_fmt_push_item(ads_decode_result_t *r, const char *type, const char *code,
+                       const char *label, const char *value);
+
+/* Time-of-day helper: seconds since midnight → "HH:MM:SS" (for < 86400);
+ * larger values stringify as-is. Caller frees the returned malloc'd string. */
+char *ads_fmt_time_of_day_str(int64_t seconds);
+
+/* ─── Result mutators ────────────────────────────────────────────────────── */
+/* For escape hatches that need to override fields the ads_result_new() call
+ * already set up (e.g. variant-dependent description, custom remaining text). */
+
+void ads_result_set_description(ads_decode_result_t *r, const char *description);
+void ads_result_set_remaining(ads_decode_result_t *r, const char *text);
+void ads_result_append_remaining(ads_decode_result_t *r, const char *text, const char *sep);
+const char *ads_result_get_remaining(const ads_decode_result_t *r);
+void ads_result_set_decode_level(ads_decode_result_t *r, ads_decode_level_t level);
+void ads_result_clear_items(ads_decode_result_t *r);
+
 #ifdef __cplusplus
 }
 #endif
diff --git a/runtimes/c/src/result_formatter.c b/runtimes/c/src/result_formatter.c
index e3acbaa..c2ed7a0 100644
--- a/runtimes/c/src/result_formatter.c
+++ b/runtimes/c/src/result_formatter.c
@@ -93,23 +93,221 @@ void ads_fmt_departure_airport(ads_decode_result_t *r, ads_value_t *v) { push_st
 void ads_fmt_arrival_airport(ads_decode_result_t *r, ads_value_t *v)   { push_string(r, v, "arrival_icao", "airport_destination", "ARR", "Destination"); }
 
 void ads_fmt_unknown_arr(ads_decode_result_t *r, const char *const *values, size_t count) {
+    ads_fmt_unknown_arr_sep(r, values, count, ",");
+}
+
+void ads_fmt_unknown_arr_sep(ads_decode_result_t *r, const char *const *values, size_t count, const char *sep) {
+    if (!r || !values || count == 0) return;
+    if (!sep) sep = ",";
+    size_t sep_len = strlen(sep);
     size_t total = 1;
-    for (size_t i = 0; i < count; i++) total += strlen(values[i] ? values[i] : "") + 1;
+    for (size_t i = 0; i < count; i++) total += strlen(values[i] ? values[i] : "") + sep_len;
     char *joined = malloc(total);
     if (!joined) return;
     joined[0] = '\0';
     for (size_t i = 0; i < count; i++) {
-        if (i > 0) strcat(joined, ",");
+        if (i > 0) strcat(joined, sep);
         strcat(joined, values[i] ? values[i] : "");
     }
+    ads_result_append_remaining(r, joined, sep);
+    free(joined);
+}
+
+void ads_fmt_unknown(ads_decode_result_t *r, const char *value) {
+    ads_result_append_remaining(r, value, ",");
+}
+
+void ads_fmt_unknown_sep(ads_decode_result_t *r, const char *value, const char *sep) {
+    ads_result_append_remaining(r, value, sep);
+}
+
+/* ─── Time-of-day helper ─────────────────────────────────────────────────── */
+
+char *ads_fmt_time_of_day_str(int64_t seconds) {
+    char *out = malloc(16);
+    if (!out) return NULL;
+    if (seconds >= 0 && seconds < 86400) {
+        int h = (int)(seconds / 3600);
+        int m = (int)((seconds % 3600) / 60);
+        int s = (int)(seconds % 60);
+        snprintf(out, 16, "%02d:%02d:%02d", h, m, s);
+    } else {
+        snprintf(out, 16, "%lld", (long long)seconds);
+    }
+    return out;
+}
+
+/* ─── Time-of-day formatters (value in seconds since midnight) ───────────── */
+
+static void push_tod(ads_decode_result_t *r, ads_value_t *v, const char *raw_key,
+                     const char *kind, const char *code, const char *label) {
+    if (!v) return;
+    int64_t n = 0;
+    ads_value_as_int(v, &n);
+    cJSON_AddNumberToObject(r->raw, raw_key, (double)n);
+    char *display = ads_fmt_time_of_day_str(n);
+    push_item(r, kind, code, label, display ? display : "");
+    free(display);
+    ads_value_free(v);
+}
+
+void ads_fmt_eta(ads_decode_result_t *r, ads_value_t *v) {
+    push_tod(r, v, "eta_time", "time", "ETA", "Estimated Time of Arrival");
+}
+void ads_fmt_off(ads_decode_result_t *r, ads_value_t *v) {
+    push_tod(r, v, "off_time", "time", "OFF", "Takeoff Time");
+}
+void ads_fmt_on(ads_decode_result_t *r, ads_value_t *v) {
+    push_tod(r, v, "on_time", "time", "ON", "Landing Time");
+}
+void ads_fmt_in(ads_decode_result_t *r, ads_value_t *v) {
+    push_tod(r, v, "in_time", "time", "IN", "Arrival at Gate");
+}
+void ads_fmt_out(ads_decode_result_t *r, ads_value_t *v) {
+    push_tod(r, v, "out_time", "time", "OUT", "Departure from Gate");
+}
+
+/* ─── Calendar formatters ────────────────────────────────────────────────── */
+
+static void push_int_item(ads_decode_result_t *r, ads_value_t *v, const char *raw_key,
+                          const char *kind, const char *code, const char *label) {
+    if (!v) return;
+    int64_t n = 0;
+    ads_value_as_int(v, &n);
+    cJSON_AddNumberToObject(r->raw, raw_key, (double)n);
+    char buf[32];
+    snprintf(buf, sizeof(buf), "%lld", (long long)n);
+    push_item(r, kind, code, label, buf);
+    ads_value_free(v);
+}
+
+void ads_fmt_day(ads_decode_result_t *r, ads_value_t *v)            { push_int_item(r, v, "day", "day", "MSG_DAY", "Day of Month"); }
+void ads_fmt_departure_day(ads_decode_result_t *r, ads_value_t *v)  { push_int_item(r, v, "departure_day", "day", "DEP_DAY", "Departure Day"); }
+void ads_fmt_arrival_day(ads_decode_result_t *r, ads_value_t *v)    { push_int_item(r, v, "arrival_day", "day", "ARR_DAY", "Arrival Day"); }
+void ads_fmt_month(ads_decode_result_t *r, ads_value_t *v)          { push_int_item(r, v, "month", "month", "MSG_MONTH", "Month"); }
+
+/* ─── Velocity / atmosphere formatters ───────────────────────────────────── */
+
+void ads_fmt_mach(ads_decode_result_t *r, ads_value_t *v)            { push_numeric(r, v, "mach", "mach", "MACH", "Mach", ""); }
+void ads_fmt_groundspeed(ads_decode_result_t *r, ads_value_t *v)     { push_numeric(r, v, "groundspeed", "groundspeed", "GS", "Ground Speed", "knots"); }
+void ads_fmt_airspeed(ads_decode_result_t *r, ads_value_t *v)        { push_numeric(r, v, "airspeed", "airspeed", "IAS", "Indicated Airspeed", "knots"); }
+void ads_fmt_temperature(ads_decode_result_t *r, ads_value_t *v)     { push_numeric(r, v, "outside_air_temperature", "outside_air_temperature", "OATEMP", "Outside Air Temperature (C)", "degrees"); }
+void ads_fmt_total_air_temp(ads_decode_result_t *r, ads_value_t *v)  { push_numeric(r, v, "total_air_temperature", "total_air_temperature", "TATEMP", "Total Air Temperature (C)", "degrees"); }
+
+/* ─── Fuel formatters ────────────────────────────────────────────────────── */
+
+void ads_fmt_current_fuel(ads_decode_result_t *r, ads_value_t *v)   { push_numeric(r, v, "fuel_on_board", "fuel_on_board", "FOB", "Fuel On Board", ""); }
+void ads_fmt_remaining_fuel(ads_decode_result_t *r, ads_value_t *v) { push_numeric(r, v, "fuel_remaining", "fuel_remaining", "FUEL_REM", "Fuel Remaining", ""); }
+
+/* ─── Routing formatters ─────────────────────────────────────────────────── */
+
+void ads_fmt_alternate_airport(ads_decode_result_t *r, ads_value_t *v) { push_string(r, v, "alternate_icao", "icao", "ALT_DST", "Alternate Destination"); }
+void ads_fmt_arrival_runway(ads_decode_result_t *r, ads_value_t *v)    { push_string(r, v, "arrival_runway", "runway", "ARWY", "Arrival Runway"); }
+void ads_fmt_alternate_runway(ads_decode_result_t *r, ads_value_t *v)  { push_string(r, v, "alternate_runway", "runway", "ALT_RWY", "Alternate Runway"); }
+
+/* ─── Event formatters ───────────────────────────────────────────────────── */
+
+void ads_fmt_state_change(ads_decode_result_t *r, const char *from, const char *to) {
+    if (!r || !from || !to) return;
+    cJSON *obj = cJSON_CreateObject();
+    cJSON_AddStringToObject(obj, "from", from);
+    cJSON_AddStringToObject(obj, "to", to);
+    cJSON_AddItemToObject(r->raw, "state_change", obj);
+    char buf[128];
+    snprintf(buf, sizeof(buf), "%s -> %s", from, to);
+    push_item(r, "state_change", "STATE_CHANGE", "State Change", buf);
+}
+
+void ads_fmt_door_event(ads_decode_result_t *r, const char *door, const char *state) {
+    if (!r || !door || !state) return;
+    cJSON *obj = cJSON_CreateObject();
+    cJSON_AddStringToObject(obj, "door", door);
+    cJSON_AddStringToObject(obj, "state", state);
+    cJSON_AddItemToObject(r->raw, "door_event", obj);
+    char buf[128];
+    snprintf(buf, sizeof(buf), "%s %s", door, state);
+    push_item(r, "door_event", "DOOR", "Door Event", buf);
+}
+
+/* ─── Free-text formatters ───────────────────────────────────────────────── */
+
+void ads_fmt_text(ads_decode_result_t *r, const char *value) {
+    if (!r || !value) return;
+    cJSON_AddStringToObject(r->raw, "text", value);
+    push_item(r, "text", "TEXT", "Text Message", value);
+}
+
+/* ─── Diagnostic formatters ──────────────────────────────────────────────── */
+
+void ads_fmt_checksum(ads_decode_result_t *r, ads_value_t *v) {
+    if (!v) return;
+    int64_t n = 0;
+    ads_value_as_int(v, &n);
+    cJSON_AddNumberToObject(r->raw, "checksum", (double)n);
+    char buf[32];
+    snprintf(buf, sizeof(buf), "%llx", (long long)n);
+    push_item(r, "checksum", "CKSUM", "Checksum", buf);
+    ads_value_free(v);
+}
+
+void ads_fmt_checksum_algorithm(ads_decode_result_t *r, const char *value) {
+    if (!r || !value) return;
+    cJSON_AddStringToObject(r->raw, "checksum_algorithm", value);
+    push_item(r, "checksum_algorithm", "CKSUM_ALGO", "Checksum Algorithm", value);
+}
+
+/* ─── Generic structured-item push ───────────────────────────────────────── */
+
+void ads_fmt_push_item(ads_decode_result_t *r, const char *type, const char *code,
+                       const char *label, const char *value) {
+    if (!r) return;
+    push_item(r,
+              type  ? type  : "unknown",
+              code  ? code  : "",
+              label ? label : "",
+              value ? value : "");
+}
+
+/* ─── Result mutators (declared in ads_helpers.h) ────────────────────────── */
+
+void ads_result_set_description(ads_decode_result_t *r, const char *description) {
+    if (!r) return;
+    free(r->description);
+    r->description = description ? strdup(description) : NULL;
+}
+
+void ads_result_set_remaining(ads_decode_result_t *r, const char *text) {
+    if (!r) return;
+    free(r->remaining);
+    r->remaining = text ? strdup(text) : NULL;
+}
+
+void ads_result_append_remaining(ads_decode_result_t *r, const char *text, const char *sep) {
+    if (!r || !text) return;
+    if (!sep) sep = ",";
     if (r->remaining) {
-        size_t newlen = strlen(r->remaining) + 1 + strlen(joined) + 1;
+        size_t newlen = strlen(r->remaining) + strlen(sep) + strlen(text) + 1;
         char *grown = malloc(newlen);
-        snprintf(grown, newlen, "%s,%s", r->remaining, joined);
+        if (!grown) return;
+        snprintf(grown, newlen, "%s%s%s", r->remaining, sep, text);
         free(r->remaining);
         r->remaining = grown;
     } else {
-        r->remaining = strdup(joined);
+        r->remaining = strdup(text);
     }
-    free(joined);
+}
+
+const char *ads_result_get_remaining(const ads_decode_result_t *r) {
+    return r ? r->remaining : NULL;
+}
+
+void ads_result_set_decode_level(ads_decode_result_t *r, ads_decode_level_t level) {
+    if (!r) return;
+    r->decode_level = level;
+}
+
+void ads_result_clear_items(ads_decode_result_t *r) {
+    if (!r) return;
+    cJSON_Delete(r->items);
+    r->items = cJSON_CreateArray();
 }