diff --git a/server/channelserver/rengoku_build.go b/server/channelserver/rengoku_build.go
new file mode 100644
index 000000000..c48efde0f
--- /dev/null
+++ b/server/channelserver/rengoku_build.go
@@ -0,0 +1,270 @@
+package channelserver
+
+/*
+	JSON-based rengoku_data.bin builder.
+
+	Operators can place rengoku_data.json in the bin/ directory instead of
+	(or alongside) rengoku_data.bin. When the JSON file is found it takes
+	precedence: it is parsed, validated, assembled into the raw binary layout,
+	and ECD-encrypted before being cached. The .bin file is used as a fallback.
+
+	Binary layout produced by BuildRengokuBinary:
+	  0x00–0x13  header  (20 bytes: magic + version + zeros)
+	  0x14–0x2B  multiDef RoadMode  (24 bytes)
+	  0x2C–0x43  soloDef  RoadMode  (24 bytes)
+	  -- multi road data --
+	  floorStats[]          (floorStatsCount × 24 bytes)
+	  spawnTablePtrs[]      (spawnTablePtrCount × 4 bytes)
+	  spawnCountPtrs[]      (spawnTablePtrCount × 4 bytes, zeroed)
+	  spawnTables[]         (spawnTablePtrCount × 32 bytes)
+	  -- solo road data --  (same sub-layout)
+*/
+
+import (
+	"encoding/binary"
+	"encoding/json"
+	"fmt"
+	"math"
+	"os"
+	"path/filepath"
+
+	"erupe-ce/common/decryption"
+
+	"go.uber.org/zap"
+)
+
+// ─── JSON schema ────────────────────────────────────────────────────────────
+
+// RengokuConfig is the top-level JSON structure for rengoku_data.json.
+type RengokuConfig struct {
+	MultiRoad RoadConfig `json:"multi_road"`
+	SoloRoad  RoadConfig `json:"solo_road"`
+}
+
+// RoadConfig describes one road mode (multi or solo) with its floors and
+// spawn tables. Floors reference spawn tables by zero-based index.
+type RoadConfig struct {
+	Floors      []FloorConfig      `json:"floors"`
+	SpawnTables []SpawnTableConfig `json:"spawn_tables"`
+}
+
+// FloorConfig describes one floor within a road mode.
+//
+//   - SpawnTableIndex: zero-based index into this road's SpawnTables slice,
+//     selecting which monster configuration is active on this floor.
+//   - PointMulti1/2: point multipliers applied to rewards on this floor.
+//   - FinalLoop: non-zero on the last floor of a loop cycle.
+type FloorConfig struct {
+	FloorNumber     uint32  `json:"floor_number"`
+	SpawnTableIndex uint32  `json:"spawn_table_index"`
+	Unk0            uint32  `json:"unk0,omitempty"`
+	PointMulti1     float32 `json:"point_multi_1"`
+	PointMulti2     float32 `json:"point_multi_2"`
+	FinalLoop       uint32  `json:"final_loop,omitempty"`
+}
+
+// SpawnTableConfig describes the two monsters that appear together on a floor.
+type SpawnTableConfig struct {
+	Monster1ID      uint32 `json:"monster1_id"`
+	Monster1Variant uint32 `json:"monster1_variant,omitempty"`
+	Monster2ID      uint32 `json:"monster2_id"`
+	Monster2Variant uint32 `json:"monster2_variant,omitempty"`
+	StatTable       uint32 `json:"stat_table,omitempty"`
+	MapZoneOverride uint32 `json:"map_zone_override,omitempty"`
+	SpawnWeighting  uint32 `json:"spawn_weighting,omitempty"`
+	AdditionalFlag  uint32 `json:"additional_flag,omitempty"`
+}
+
+// ─── Builder ─────────────────────────────────────────────────────────────────
+
+// BuildRengokuBinary assembles a raw (unencrypted, uncompressed) rengoku
+// binary from a RengokuConfig. The result can be passed to EncodeECD and
+// served directly to clients.
+func BuildRengokuBinary(cfg RengokuConfig) ([]byte, error) {
+	if err := validateRengokuConfig(cfg); err != nil {
+		return nil, err
+	}
+
+	// ── Offset plan ──────────────────────────────────────────────────────────
+	// Fixed regions: header (0x14) + two RoadModes (2×24) = 0x44
+	const dataStart = uint32(rengokuMinSize) // 0x44
+
+	// Multi road sections
+	mFloorOff := dataStart
+	mFloorSz := uint32(len(cfg.MultiRoad.Floors)) * floorStatsByteSize
+	mPtrsOff := mFloorOff + mFloorSz
+	mPtrsSz := uint32(len(cfg.MultiRoad.SpawnTables)) * spawnPtrEntrySize
+	mCntOff := mPtrsOff + mPtrsSz
+	mCntSz := uint32(len(cfg.MultiRoad.SpawnTables)) * spawnPtrEntrySize
+	mTablesOff := mCntOff + mCntSz
+	mTablesSz := uint32(len(cfg.MultiRoad.SpawnTables)) * spawnTableByteSize
+
+	// Solo road sections (appended directly after multi)
+	sFloorOff := mTablesOff + mTablesSz
+	sFloorSz := uint32(len(cfg.SoloRoad.Floors)) * floorStatsByteSize
+	sPtrsOff := sFloorOff + sFloorSz
+	sPtrsSz := uint32(len(cfg.SoloRoad.SpawnTables)) * spawnPtrEntrySize
+	sCntOff := sPtrsOff + sPtrsSz
+	sCntSz := uint32(len(cfg.SoloRoad.SpawnTables)) * spawnPtrEntrySize
+	sTablesOff := sCntOff + sCntSz
+	sTablesSz := uint32(len(cfg.SoloRoad.SpawnTables)) * spawnTableByteSize
+
+	totalSize := sTablesOff + sTablesSz
+	buf := make([]byte, totalSize)
+
+	// ── Header ───────────────────────────────────────────────────────────────
+	buf[0], buf[1], buf[2], buf[3] = 'r', 'e', 'f', 0x1A
+	buf[4] = 1 // version
+
+	le := binary.LittleEndian
+
+	// ── RoadMode structs ─────────────────────────────────────────────────────
+	writeRoadMode(buf, 0x14, le, RoadModeFields{
+		FloorCount:   uint32(len(cfg.MultiRoad.Floors)),
+		SpawnCount:   uint32(len(cfg.MultiRoad.SpawnTables)),
+		TablePtrCnt:  uint32(len(cfg.MultiRoad.SpawnTables)),
+		FloorPtr:     mFloorOff,
+		TablePtrsPtr: mPtrsOff,
+		CountPtrsPtr: mCntOff,
+	})
+	writeRoadMode(buf, 0x2C, le, RoadModeFields{
+		FloorCount:   uint32(len(cfg.SoloRoad.Floors)),
+		SpawnCount:   uint32(len(cfg.SoloRoad.SpawnTables)),
+		TablePtrCnt:  uint32(len(cfg.SoloRoad.SpawnTables)),
+		FloorPtr:     sFloorOff,
+		TablePtrsPtr: sPtrsOff,
+		CountPtrsPtr: sCntOff,
+	})
+
+	// ── Data sections ────────────────────────────────────────────────────────
+	writeFloors(buf, cfg.MultiRoad.Floors, mFloorOff, le)
+	writeSpawnSection(buf, cfg.MultiRoad.SpawnTables, mPtrsOff, mTablesOff, le)
+
+	writeFloors(buf, cfg.SoloRoad.Floors, sFloorOff, le)
+	writeSpawnSection(buf, cfg.SoloRoad.SpawnTables, sPtrsOff, sTablesOff, le)
+
+	return buf, nil
+}
+
+// RoadModeFields carries the computed field values for one RoadMode struct.
+type RoadModeFields struct {
+	FloorCount, SpawnCount, TablePtrCnt uint32
+	FloorPtr, TablePtrsPtr, CountPtrsPtr uint32
+}
+
+func writeRoadMode(buf []byte, offset int, le binary.ByteOrder, f RoadModeFields) {
+	le.PutUint32(buf[offset:], f.FloorCount)
+	le.PutUint32(buf[offset+4:], f.SpawnCount)
+	le.PutUint32(buf[offset+8:], f.TablePtrCnt)
+	le.PutUint32(buf[offset+12:], f.FloorPtr)
+	le.PutUint32(buf[offset+16:], f.TablePtrsPtr)
+	le.PutUint32(buf[offset+20:], f.CountPtrsPtr)
+}
+
+func writeFloors(buf []byte, floors []FloorConfig, base uint32, le binary.ByteOrder) {
+	for i, f := range floors {
+		off := base + uint32(i)*floorStatsByteSize
+		le.PutUint32(buf[off:], f.FloorNumber)
+		le.PutUint32(buf[off+4:], f.SpawnTableIndex)
+		le.PutUint32(buf[off+8:], f.Unk0)
+		le.PutUint32(buf[off+12:], math.Float32bits(f.PointMulti1))
+		le.PutUint32(buf[off+16:], math.Float32bits(f.PointMulti2))
+		le.PutUint32(buf[off+20:], f.FinalLoop)
+	}
+}
+
+func writeSpawnSection(buf []byte, tables []SpawnTableConfig, ptrsBase, tablesBase uint32, le binary.ByteOrder) {
+	for i, t := range tables {
+		tableOff := tablesBase + uint32(i)*spawnTableByteSize
+		// Pointer entry
+		le.PutUint32(buf[ptrsBase+uint32(i)*spawnPtrEntrySize:], tableOff)
+		// SpawnTable (32 bytes)
+		le.PutUint32(buf[tableOff:], t.Monster1ID)
+		le.PutUint32(buf[tableOff+4:], t.Monster1Variant)
+		le.PutUint32(buf[tableOff+8:], t.Monster2ID)
+		le.PutUint32(buf[tableOff+12:], t.Monster2Variant)
+		le.PutUint32(buf[tableOff+16:], t.StatTable)
+		le.PutUint32(buf[tableOff+20:], t.MapZoneOverride)
+		le.PutUint32(buf[tableOff+24:], t.SpawnWeighting)
+		le.PutUint32(buf[tableOff+28:], t.AdditionalFlag)
+	}
+}
+
+// validateRengokuConfig checks that all spawn_table_index references are
+// within range for both road modes.
+func validateRengokuConfig(cfg RengokuConfig) error {
+	for _, road := range []struct {
+		name  string
+		r     RoadConfig
+	}{{"multi_road", cfg.MultiRoad}, {"solo_road", cfg.SoloRoad}} {
+		n := len(road.r.SpawnTables)
+		for i, f := range road.r.Floors {
+			if int(f.SpawnTableIndex) >= n {
+				return fmt.Errorf("rengoku: %s floor %d: spawn_table_index %d out of range (have %d tables)",
+					road.name, i, f.SpawnTableIndex, n)
+			}
+		}
+	}
+	return nil
+}
+
+// ─── Shared helper ───────────────────────────────────────────────────────────
+
+// encodeRengokuECD wraps decryption.EncodeECD with error logging.
+func encodeRengokuECD(raw []byte, logger *zap.Logger) ([]byte, error) {
+	enc, err := decryption.EncodeECD(raw, decryption.DefaultECDKey)
+	if err != nil {
+		logger.Error("rengoku: ECD encryption failed", zap.Error(err))
+	}
+	return enc, err
+}
+
+// ─── JSON loader ─────────────────────────────────────────────────────────────
+
+// loadRengokuFromJSON attempts to load rengoku configuration from
+// rengoku_data.json in binPath. It returns the ECD-encrypted binary ready for
+// caching, or nil if the file is absent or cannot be processed.
+func loadRengokuFromJSON(binPath string, logger *zap.Logger) []byte {
+	path := filepath.Join(binPath, "rengoku_data.json")
+	raw, err := os.ReadFile(path)
+	if err != nil {
+		return nil // file absent — not an error
+	}
+
+	var cfg RengokuConfig
+	if err := json.Unmarshal(raw, &cfg); err != nil {
+		logger.Error("rengoku_data.json: JSON parse error",
+			zap.String("path", path), zap.Error(err))
+		return nil
+	}
+
+	bin, err := BuildRengokuBinary(cfg)
+	if err != nil {
+		logger.Error("rengoku_data.json: binary build failed",
+			zap.String("path", path), zap.Error(err))
+		return nil
+	}
+
+	// Validate the freshly built binary (should always pass, but good to confirm).
+	info, parseErr := parseRengokuBinary(bin)
+	if parseErr != nil {
+		logger.Error("rengoku_data.json: structural validation of built binary failed",
+			zap.String("path", path), zap.Error(parseErr))
+		return nil
+	}
+
+	enc, err := encodeRengokuECD(bin, logger)
+	if err != nil {
+		return nil
+	}
+
+	logger.Info("Hunting Road config (from JSON)",
+		zap.Int("multi_floors", info.MultiFloors),
+		zap.Int("multi_spawn_tables", info.MultiSpawnTables),
+		zap.Int("solo_floors", info.SoloFloors),
+		zap.Int("solo_spawn_tables", info.SoloSpawnTables),
+		zap.Int("unique_monsters", info.UniqueMonsters),
+	)
+	logger.Info("Loaded rengoku_data.json", zap.Int("bytes", len(enc)))
+	return enc
+}
diff --git a/server/channelserver/rengoku_build_test.go b/server/channelserver/rengoku_build_test.go
new file mode 100644
index 000000000..5fcf9a3a1
--- /dev/null
+++ b/server/channelserver/rengoku_build_test.go
@@ -0,0 +1,217 @@
+package channelserver
+
+import (
+	"encoding/json"
+	"math"
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
+
+	"go.uber.org/zap"
+)
+
+// sampleRengokuConfig returns a small but complete RengokuConfig for tests.
+func sampleRengokuConfig() RengokuConfig {
+	spawnTables := []SpawnTableConfig{
+		{Monster1ID: 101, Monster1Variant: 0, Monster2ID: 102, Monster2Variant: 1,
+			StatTable: 3, SpawnWeighting: 10},
+		{Monster1ID: 103, Monster1Variant: 2, Monster2ID: 104, Monster2Variant: 0,
+			SpawnWeighting: 20},
+	}
+	floors := []FloorConfig{
+		{FloorNumber: 1, SpawnTableIndex: 0, PointMulti1: 1.0, PointMulti2: 1.5},
+		{FloorNumber: 2, SpawnTableIndex: 1, PointMulti1: 1.2, PointMulti2: 2.0},
+		{FloorNumber: 3, SpawnTableIndex: 0, PointMulti1: 1.5, PointMulti2: 2.5, FinalLoop: 1},
+	}
+	soloFloors := []FloorConfig{
+		{FloorNumber: 1, SpawnTableIndex: 0, PointMulti1: 1.0, PointMulti2: 1.5},
+		{FloorNumber: 2, SpawnTableIndex: 0, PointMulti1: 1.2, PointMulti2: 2.0},
+	}
+	return RengokuConfig{
+		MultiRoad: RoadConfig{Floors: floors, SpawnTables: spawnTables},
+		SoloRoad:  RoadConfig{Floors: soloFloors, SpawnTables: spawnTables[1:]},
+	}
+}
+
+// TestBuildRengokuBinary_RoundTrip builds a binary from a config and verifies
+// that parseRengokuBinary accepts it and reports the expected summary.
+func TestBuildRengokuBinary_RoundTrip(t *testing.T) {
+	cfg := sampleRengokuConfig()
+
+	bin, err := BuildRengokuBinary(cfg)
+	if err != nil {
+		t.Fatalf("BuildRengokuBinary: %v", err)
+	}
+
+	info, err := parseRengokuBinary(bin)
+	if err != nil {
+		t.Fatalf("parseRengokuBinary on built binary: %v", err)
+	}
+
+	if info.MultiFloors != len(cfg.MultiRoad.Floors) {
+		t.Errorf("MultiFloors = %d, want %d", info.MultiFloors, len(cfg.MultiRoad.Floors))
+	}
+	if info.MultiSpawnTables != len(cfg.MultiRoad.SpawnTables) {
+		t.Errorf("MultiSpawnTables = %d, want %d", info.MultiSpawnTables, len(cfg.MultiRoad.SpawnTables))
+	}
+	if info.SoloFloors != len(cfg.SoloRoad.Floors) {
+		t.Errorf("SoloFloors = %d, want %d", info.SoloFloors, len(cfg.SoloRoad.Floors))
+	}
+	if info.SoloSpawnTables != len(cfg.SoloRoad.SpawnTables) {
+		t.Errorf("SoloSpawnTables = %d, want %d", info.SoloSpawnTables, len(cfg.SoloRoad.SpawnTables))
+	}
+	// Unique monsters: multi has 101,102,103,104; solo has 103,104 → 4 total
+	if info.UniqueMonsters != 4 {
+		t.Errorf("UniqueMonsters = %d, want 4", info.UniqueMonsters)
+	}
+}
+
+// TestBuildRengokuBinary_FloatFields verifies that PointMulti1/2 values
+// survive the binary encoding intact.
+func TestBuildRengokuBinary_FloatFields(t *testing.T) {
+	cfg := RengokuConfig{
+		MultiRoad: RoadConfig{
+			Floors: []FloorConfig{
+				{FloorNumber: 1, SpawnTableIndex: 0, PointMulti1: 1.25, PointMulti2: 3.75},
+			},
+			SpawnTables: []SpawnTableConfig{{Monster1ID: 1}},
+		},
+		SoloRoad: RoadConfig{
+			Floors:      []FloorConfig{{FloorNumber: 1, SpawnTableIndex: 0}},
+			SpawnTables: []SpawnTableConfig{{Monster1ID: 2}},
+		},
+	}
+
+	bin, err := BuildRengokuBinary(cfg)
+	if err != nil {
+		t.Fatalf("BuildRengokuBinary: %v", err)
+	}
+
+	// Re-parse the binary and check that we can read back the float fields.
+	// The floor stats for multiDef start at rengokuMinSize (0x44).
+	// Layout: floorNumber(4) + spawnTableIndex(4) + unk0(4) + pointMulti1(4) + pointMulti2(4)
+	floorBase := rengokuMinSize // 0x44
+	pm1Bits := uint32(bin[floorBase+12]) | uint32(bin[floorBase+13])<<8 |
+		uint32(bin[floorBase+14])<<16 | uint32(bin[floorBase+15])<<24
+	pm2Bits := uint32(bin[floorBase+16]) | uint32(bin[floorBase+17])<<8 |
+		uint32(bin[floorBase+18])<<16 | uint32(bin[floorBase+19])<<24
+
+	if got := math.Float32frombits(pm1Bits); got != 1.25 {
+		t.Errorf("PointMulti1 = %f, want 1.25", got)
+	}
+	if got := math.Float32frombits(pm2Bits); got != 3.75 {
+		t.Errorf("PointMulti2 = %f, want 3.75", got)
+	}
+}
+
+// TestBuildRengokuBinary_ValidationErrors verifies that out-of-range
+// spawn_table_index values are caught before the binary is built.
+func TestBuildRengokuBinary_ValidationErrors(t *testing.T) {
+	cases := []struct {
+		name    string
+		cfg     RengokuConfig
+		wantErr string
+	}{
+		{
+			name: "multi_index_out_of_range",
+			cfg: RengokuConfig{
+				MultiRoad: RoadConfig{
+					Floors:      []FloorConfig{{FloorNumber: 1, SpawnTableIndex: 5}},
+					SpawnTables: []SpawnTableConfig{{Monster1ID: 1}},
+				},
+				SoloRoad: RoadConfig{
+					Floors:      []FloorConfig{{FloorNumber: 1, SpawnTableIndex: 0}},
+					SpawnTables: []SpawnTableConfig{{Monster1ID: 2}},
+				},
+			},
+			wantErr: "multi_road",
+		},
+		{
+			name: "solo_index_out_of_range",
+			cfg: RengokuConfig{
+				MultiRoad: RoadConfig{
+					Floors:      []FloorConfig{{FloorNumber: 1, SpawnTableIndex: 0}},
+					SpawnTables: []SpawnTableConfig{{Monster1ID: 1}},
+				},
+				SoloRoad: RoadConfig{
+					Floors:      []FloorConfig{{FloorNumber: 1, SpawnTableIndex: 99}},
+					SpawnTables: []SpawnTableConfig{{Monster1ID: 2}},
+				},
+			},
+			wantErr: "solo_road",
+		},
+	}
+
+	for _, tc := range cases {
+		t.Run(tc.name, func(t *testing.T) {
+			_, err := BuildRengokuBinary(tc.cfg)
+			if err == nil {
+				t.Fatal("expected error, got nil")
+			}
+			if !strings.Contains(err.Error(), tc.wantErr) {
+				t.Errorf("error %q does not contain %q", err.Error(), tc.wantErr)
+			}
+		})
+	}
+}
+
+// TestLoadRengokuBinary_JSONPreferredOverBin writes both a JSON file and a
+// .bin file and verifies that the JSON source is used (different monster IDs).
+func TestLoadRengokuBinary_JSONPreferredOverBin(t *testing.T) {
+	dir := t.TempDir()
+	logger, _ := zap.NewDevelopment()
+
+	// Write a valid rengoku_data.json
+	cfg := sampleRengokuConfig()
+	jsonBytes, err := json.Marshal(cfg)
+	if err != nil {
+		t.Fatalf("marshal: %v", err)
+	}
+	if err := os.WriteFile(filepath.Join(dir, "rengoku_data.json"), jsonBytes, 0644); err != nil {
+		t.Fatal(err)
+	}
+
+	// Also write a minimal (but incompletely valid) rengoku_data.bin that
+	// would be returned if JSON loading was skipped.
+	binData := make([]byte, 16) // 16-byte ECD header, zero payload
+	binData[0], binData[1], binData[2], binData[3] = 0x65, 0x63, 0x64, 0x1A
+	if err := os.WriteFile(filepath.Join(dir, "rengoku_data.bin"), binData, 0644); err != nil {
+		t.Fatal(err)
+	}
+
+	result := loadRengokuBinary(dir, logger)
+	if result == nil {
+		t.Fatal("expected non-nil result from JSON loading")
+	}
+	// The JSON-built binary is longer than the 16-byte stub .bin.
+	if len(result) <= 16 {
+		t.Errorf("result is %d bytes — looks like .bin was used instead of JSON", len(result))
+	}
+}
+
+// TestLoadRengokuBinary_JSONFallsThroughOnBadJSON verifies that a malformed
+// JSON file causes loadRengokuBinary to fall back to the .bin file.
+func TestLoadRengokuBinary_JSONFallsThroughOnBadJSON(t *testing.T) {
+	dir := t.TempDir()
+	logger, _ := zap.NewDevelopment()
+
+	if err := os.WriteFile(filepath.Join(dir, "rengoku_data.json"), []byte("{invalid json"), 0644); err != nil {
+		t.Fatal(err)
+	}
+
+	// Write a valid minimal .bin
+	binData := make([]byte, 16)
+	binData[0], binData[1], binData[2], binData[3] = 0x65, 0x63, 0x64, 0x1A
+	if err := os.WriteFile(filepath.Join(dir, "rengoku_data.bin"), binData, 0644); err != nil {
+		t.Fatal(err)
+	}
+
+	result := loadRengokuBinary(dir, logger)
+	if result == nil {
+		t.Fatal("expected fallback to .bin, got nil")
+	}
+	if len(result) != 16 {
+		t.Errorf("expected 16-byte .bin result, got %d bytes", len(result))
+	}
+}
diff --git a/server/channelserver/sys_channel_server.go b/server/channelserver/sys_channel_server.go
index 4d4357b06..5edd1dab7 100644
--- a/server/channelserver/sys_channel_server.go
+++ b/server/channelserver/sys_channel_server.go
@@ -450,12 +450,15 @@ func (s *Server) Season() uint8 {
 	return uint8(((TimeAdjusted().Unix() / secsPerDay) + sid) % 3)
 }
 
-// loadRengokuBinary reads, validates, and caches rengoku_data.bin from binPath.
-// The file is served to clients as-is (ECD-encrypted); decryption and parsing
-// are performed only for structural validation and startup logging.
-// Returns the raw encrypted bytes on success, or nil if the file is
-// missing or structurally invalid.
+// loadRengokuBinary loads and caches Hunting Road config. It prefers
+// rengoku_data.json (human-readable, built on the fly) and falls back to the
+// pre-encrypted rengoku_data.bin. Returns ECD-encrypted bytes ready to serve,
+// or nil if no valid source is found.
 func loadRengokuBinary(binPath string, logger *zap.Logger) []byte {
+	if enc := loadRengokuFromJSON(binPath, logger); enc != nil {
+		return enc
+	}
+
 	path := filepath.Join(binPath, "rengoku_data.bin")
 	data, err := os.ReadFile(path)
 	if err != nil {