diff --git a/proxyd/proxyd/config.go b/proxyd/proxyd/config.go
index ba60d67..0647074 100644
--- a/proxyd/proxyd/config.go
+++ b/proxyd/proxyd/config.go
@@ -95,19 +95,26 @@ type BackendGroupsConfig map[string]*BackendGroupConfig
 
 type MethodMappingsConfig map[string]string
 
+type BatchConfig struct {
+	MaxSize      int    `toml:"max_size"`
+	ErrorMessage string `toml:"error_message"`
+}
+
 type Config struct {
-	WSBackendGroup    string              `toml:"ws_backend_group"`
-	Server            ServerConfig        `toml:"server"`
-	Cache             CacheConfig         `toml:"cache"`
-	Redis             RedisConfig         `toml:"redis"`
-	Metrics           MetricsConfig       `toml:"metrics"`
-	RateLimit         RateLimitConfig     `toml:"rate_limit"`
-	BackendOptions    BackendOptions      `toml:"backend"`
-	Backends          BackendsConfig      `toml:"backends"`
-	Authentication    map[string]string   `toml:"authentication"`
-	BackendGroups     BackendGroupsConfig `toml:"backend_groups"`
-	RPCMethodMappings map[string]string   `toml:"rpc_method_mappings"`
-	WSMethodWhitelist []string            `toml:"ws_method_whitelist"`
+	WSBackendGroup        string              `toml:"ws_backend_group"`
+	Server                ServerConfig        `toml:"server"`
+	Cache                 CacheConfig         `toml:"cache"`
+	Redis                 RedisConfig         `toml:"redis"`
+	Metrics               MetricsConfig       `toml:"metrics"`
+	RateLimit             RateLimitConfig     `toml:"rate_limit"`
+	BackendOptions        BackendOptions      `toml:"backend"`
+	Backends              BackendsConfig      `toml:"backends"`
+	BatchConfig           BatchConfig         `toml:"batch"`
+	Authentication        map[string]string   `toml:"authentication"`
+	BackendGroups         BackendGroupsConfig `toml:"backend_groups"`
+	RPCMethodMappings     map[string]string   `toml:"rpc_method_mappings"`
+	WSMethodWhitelist     []string            `toml:"ws_method_whitelist"`
+	WhitelistErrorMessage string              `toml:"whitelist_error_message"`
 }
 
 func ReadFromEnvOrConfig(value string) (string, error) {
diff --git a/proxyd/proxyd/integration_tests/batching_test.go b/proxyd/proxyd/integration_tests/batching_test.go
index 1bcbba9..b0f811c 100644
--- a/proxyd/proxyd/integration_tests/batching_test.go
+++ b/proxyd/proxyd/integration_tests/batching_test.go
@@ -33,13 +33,13 @@ func TestBatching(t *testing.T) {
 	callMock1 := mockResult{"eth_call", "1", "ekans1"}
 
 	tests := []struct {
-		name                string
-		handler             http.Handler
-		mocks               []mockResult
-		reqs                []*proxyd.RPCReq
-		expectedRes         string
-		maxBatchSize        int
-		numExpectedForwards int
+		name                 string
+		handler              http.Handler
+		mocks                []mockResult
+		reqs                 []*proxyd.RPCReq
+		expectedRes          string
+		maxUpstreamBatchSize int
+		numExpectedForwards  int
 	}{
 		{
 			name:  "backend returns batches out of order",
@@ -49,9 +49,9 @@ func TestBatching(t *testing.T) {
 				NewRPCReq("2", "eth_chainId", nil),
 				NewRPCReq("3", "eth_chainId", nil),
 			},
-			expectedRes:         asArray(chainIDResponse1, chainIDResponse2, chainIDResponse3),
-			maxBatchSize:        2,
-			numExpectedForwards: 2,
+			expectedRes:          asArray(chainIDResponse1, chainIDResponse2, chainIDResponse3),
+			maxUpstreamBatchSize: 2,
+			numExpectedForwards:  2,
 		},
 		{
 			// infura behavior
@@ -65,8 +65,8 @@ func TestBatching(t *testing.T) {
 				`{"error":{"code":-32011,"message":"no backends available for method"},"id":1,"jsonrpc":"2.0"}`,
 				`{"error":{"code":-32011,"message":"no backends available for method"},"id":2,"jsonrpc":"2.0"}`,
 			),
-			maxBatchSize:        10,
-			numExpectedForwards: 1,
+			maxUpstreamBatchSize: 10,
+			numExpectedForwards:  1,
 		},
 		{
 			name:    "backend returns single RPC response object for minibatches",
@@ -79,8 +79,8 @@ func TestBatching(t *testing.T) {
 				`{"error":{"code":-32011,"message":"no backends available for method"},"id":1,"jsonrpc":"2.0"}`,
 				`{"error":{"code":-32011,"message":"no backends available for method"},"id":2,"jsonrpc":"2.0"}`,
 			),
-			maxBatchSize:        1,
-			numExpectedForwards: 2,
+			maxUpstreamBatchSize: 1,
+			numExpectedForwards:  2,
 		},
 		{
 			name: "duplicate request ids are on distinct batches",
@@ -96,9 +96,24 @@ func TestBatching(t *testing.T) {
 				NewRPCReq("1", "eth_chainId", nil),
 				NewRPCReq("1", "eth_call", nil),
 			},
-			expectedRes:         asArray(netVersionResponse1, chainIDResponse2, chainIDResponse1, callResponse1),
-			maxBatchSize:        2,
-			numExpectedForwards: 3,
+			expectedRes:          asArray(netVersionResponse1, chainIDResponse2, chainIDResponse1, callResponse1),
+			maxUpstreamBatchSize: 2,
+			numExpectedForwards:  3,
+		},
+		{
+			name:  "over max size",
+			mocks: []mockResult{},
+			reqs: []*proxyd.RPCReq{
+				NewRPCReq("1", "net_version", nil),
+				NewRPCReq("2", "eth_chainId", nil),
+				NewRPCReq("3", "eth_chainId", nil),
+				NewRPCReq("4", "eth_call", nil),
+				NewRPCReq("5", "eth_call", nil),
+				NewRPCReq("6", "eth_call", nil),
+			},
+			expectedRes:          "{\"error\":{\"code\":-32014,\"message\":\"over batch size custom message\"},\"id\":null,\"jsonrpc\":\"2.0\"}",
+			maxUpstreamBatchSize: 2,
+			numExpectedForwards:  0,
 		},
 		{
 			name: "eth_accounts does not get forwarded",
@@ -109,15 +124,15 @@ func TestBatching(t *testing.T) {
 				NewRPCReq("1", "eth_call", nil),
 				NewRPCReq("2", "eth_accounts", nil),
 			},
-			expectedRes:         asArray(callResponse1, ethAccountsResponse2),
-			maxBatchSize:        2,
-			numExpectedForwards: 1,
+			expectedRes:          asArray(callResponse1, ethAccountsResponse2),
+			maxUpstreamBatchSize: 2,
+			numExpectedForwards:  1,
 		},
 	}
 
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
-			config.Server.MaxUpstreamBatchSize = tt.maxBatchSize
+			config.Server.MaxUpstreamBatchSize = tt.maxUpstreamBatchSize
 
 			handler := tt.handler
 			if handler == nil {
diff --git a/proxyd/proxyd/integration_tests/testdata/batching.toml b/proxyd/proxyd/integration_tests/testdata/batching.toml
index 2aa591d..4762835 100644
--- a/proxyd/proxyd/integration_tests/testdata/batching.toml
+++ b/proxyd/proxyd/integration_tests/testdata/batching.toml
@@ -17,3 +17,7 @@ backends = ["good"]
 eth_chainId = "main"
 net_version = "main"
 eth_call = "main"
+
+[batch]
+error_message = "over batch size custom message"
+max_size = 5
\ No newline at end of file
diff --git a/proxyd/proxyd/integration_tests/testdata/whitelist.toml b/proxyd/proxyd/integration_tests/testdata/whitelist.toml
index 55b118c..4a65248 100644
--- a/proxyd/proxyd/integration_tests/testdata/whitelist.toml
+++ b/proxyd/proxyd/integration_tests/testdata/whitelist.toml
@@ -1,3 +1,5 @@
+whitelist_error_message = "rpc method is not whitelisted custom message"
+
 [server]
 rpc_port = 8545
 
diff --git a/proxyd/proxyd/integration_tests/testdata/ws.toml b/proxyd/proxyd/integration_tests/testdata/ws.toml
index f86b22f..4642e6b 100644
--- a/proxyd/proxyd/integration_tests/testdata/ws.toml
+++ b/proxyd/proxyd/integration_tests/testdata/ws.toml
@@ -1,3 +1,5 @@
+whitelist_error_message = "rpc method is not whitelisted"
+
 ws_backend_group = "main"
 
 ws_method_whitelist = [
diff --git a/proxyd/proxyd/integration_tests/validation_test.go b/proxyd/proxyd/integration_tests/validation_test.go
index be964c1..6f0653d 100644
--- a/proxyd/proxyd/integration_tests/validation_test.go
+++ b/proxyd/proxyd/integration_tests/validation_test.go
@@ -10,7 +10,7 @@ import (
 )
 
 const (
-	notWhitelistedResponse        = `{"jsonrpc":"2.0","error":{"code":-32001,"message":"rpc method is not whitelisted"},"id":999}`
+	notWhitelistedResponse        = `{"jsonrpc":"2.0","error":{"code":-32001,"message":"rpc method is not whitelisted custom message"},"id":999}`
 	parseErrResponse              = `{"jsonrpc":"2.0","error":{"code":-32700,"message":"parse error"},"id":null}`
 	invalidJSONRPCVersionResponse = `{"error":{"code":-32601,"message":"invalid JSON-RPC version"},"id":null,"jsonrpc":"2.0"}`
 	invalidIDResponse             = `{"error":{"code":-32601,"message":"invalid ID"},"id":null,"jsonrpc":"2.0"}`
diff --git a/proxyd/proxyd/integration_tests/ws_test.go b/proxyd/proxyd/integration_tests/ws_test.go
index d93d3a7..9ae12ab 100644
--- a/proxyd/proxyd/integration_tests/ws_test.go
+++ b/proxyd/proxyd/integration_tests/ws_test.go
@@ -7,6 +7,8 @@ import (
 	"testing"
 	"time"
 
+	"github.com/ethereum/go-ethereum/log"
+
 	"github.com/ethereum-optimism/optimism/proxyd"
 	"github.com/gorilla/websocket"
 	"github.com/stretchr/testify/require"
@@ -42,6 +44,13 @@ func TestConcurrentWSPanic(t *testing.T) {
 	require.NoError(t, err)
 	defer shutdown()
 
+	// suppress tons of log messages
+	oldHandler := log.Root().GetHandler()
+	log.Root().SetHandler(log.DiscardHandler())
+	defer func() {
+		log.Root().SetHandler(oldHandler)
+	}()
+
 	<-readyCh
 
 	var wg sync.WaitGroup
diff --git a/proxyd/proxyd/metrics.go b/proxyd/proxyd/metrics.go
index 5241dfa..a3cfe45 100644
--- a/proxyd/proxyd/metrics.go
+++ b/proxyd/proxyd/metrics.go
@@ -222,6 +222,20 @@ var (
 	}, []string{
 		"backend_name",
 	})
+
+	batchSizeHistogram = promauto.NewHistogram(prometheus.HistogramOpts{
+		Namespace: MetricsNamespace,
+		Name:      "batch_size_summary",
+		Help:      "Summary of batch sizes",
+		Buckets: []float64{
+			1,
+			5,
+			10,
+			25,
+			50,
+			100,
+		},
+	})
 )
 
 func RecordRedisError(source string) {
@@ -278,3 +292,7 @@ func RecordCacheHit(method string) {
 func RecordCacheMiss(method string) {
 	cacheMissesTotal.WithLabelValues(method).Inc()
 }
+
+func RecordBatchSize(size int) {
+	batchSizeHistogram.Observe(float64(size))
+}
diff --git a/proxyd/proxyd/proxyd.go b/proxyd/proxyd/proxyd.go
index e9bbe42..12a6a1a 100644
--- a/proxyd/proxyd/proxyd.go
+++ b/proxyd/proxyd/proxyd.go
@@ -55,6 +55,20 @@ func Start(config *Config) (func(), error) {
 		}
 	}
 
+	// While modifying shared globals is a bad practice, the alternative
+	// is to clone these errors on every invocation. This is inefficient.
+	// We'd also have to make sure that errors.Is and errors.As continue
+	// to function properly on the cloned errors.
+	if config.RateLimit.ErrorMessage != "" {
+		ErrOverRateLimit.Message = config.RateLimit.ErrorMessage
+	}
+	if config.WhitelistErrorMessage != "" {
+		ErrMethodNotWhitelisted.Message = config.WhitelistErrorMessage
+	}
+	if config.BatchConfig.ErrorMessage != "" {
+		ErrTooManyBatchRequests.Message = config.BatchConfig.ErrorMessage
+	}
+
 	maxConcurrentRPCs := config.Server.MaxConcurrentRPCs
 	if maxConcurrentRPCs == 0 {
 		maxConcurrentRPCs = math.MaxInt64
@@ -225,6 +239,7 @@ func Start(config *Config) (func(), error) {
 		config.RateLimit,
 		config.Server.EnableRequestLog,
 		config.Server.MaxRequestBodyLogLen,
+		config.BatchConfig.MaxSize,
 	)
 	if err != nil {
 		return nil, fmt.Errorf("error creating server: %w", err)
diff --git a/proxyd/proxyd/server.go b/proxyd/proxyd/server.go
index 455989d..94787d1 100644
--- a/proxyd/proxyd/server.go
+++ b/proxyd/proxyd/server.go
@@ -28,7 +28,7 @@ const (
 	ContextKeyAuth              = "authorization"
 	ContextKeyReqID             = "req_id"
 	ContextKeyXForwardedFor     = "x_forwarded_for"
-	MaxBatchRPCCalls            = 100
+	MaxBatchRPCCallsHardLimit   = 100
 	cacheStatusHdr              = "X-Proxyd-Cache-Status"
 	defaultServerTimeout        = time.Second * 10
 	maxRequestBodyLogLen        = 2000
@@ -48,6 +48,7 @@ type Server struct {
 	authenticatedPaths   map[string]string
 	timeout              time.Duration
 	maxUpstreamBatchSize int
+	maxBatchSize         int
 	upgrader             *websocket.Upgrader
 	mainLim              limiter.Store
 	overrideLims         map[string]limiter.Store
@@ -75,6 +76,7 @@ func NewServer(
 	rateLimitConfig RateLimitConfig,
 	enableRequestLog bool,
 	maxRequestBodyLogLen int,
+	maxBatchSize int,
 ) (*Server, error) {
 	if cache == nil {
 		cache = &NoopRPCCache{}
@@ -92,6 +94,10 @@ func NewServer(
 		maxUpstreamBatchSize = defaultMaxUpstreamBatchSize
 	}
 
+	if maxBatchSize == 0 || maxBatchSize > MaxBatchRPCCallsHardLimit {
+		maxBatchSize = MaxBatchRPCCallsHardLimit
+	}
+
 	var mainLim limiter.Store
 	limExemptOrigins := make(map[string]bool)
 	limExemptUserAgents := make(map[string]bool)
@@ -139,6 +145,7 @@ func NewServer(
 		cache:                cache,
 		enableRequestLog:     enableRequestLog,
 		maxRequestBodyLogLen: maxRequestBodyLogLen,
+		maxBatchSize:         maxBatchSize,
 		upgrader: &websocket.Upgrader{
 			HandshakeTimeout: 5 * time.Second,
 		},
@@ -244,12 +251,7 @@ func (s *Server) HandleRPC(w http.ResponseWriter, r *http.Request) {
 	}
 
 	if isLimited("") {
-		rpcErr := ErrOverRateLimit
-		if s.limConfig.ErrorMessage != "" {
-			rpcErr = ErrOverRateLimit.Clone()
-			rpcErr.Message = s.limConfig.ErrorMessage
-		}
-		RecordRPCError(ctx, BackendProxyd, "unknown", rpcErr)
+		RecordRPCError(ctx, BackendProxyd, "unknown", ErrOverRateLimit)
 		log.Warn(
 			"rate limited request",
 			"req_id", GetReqID(ctx),
@@ -258,7 +260,7 @@ func (s *Server) HandleRPC(w http.ResponseWriter, r *http.Request) {
 			"origin", origin,
 			"remote_ip", xff,
 		)
-		writeRPCError(ctx, w, nil, rpcErr)
+		writeRPCError(ctx, w, nil, ErrOverRateLimit)
 		return
 	}
 
@@ -296,7 +298,9 @@ func (s *Server) HandleRPC(w http.ResponseWriter, r *http.Request) {
 			return
 		}
 
-		if len(reqs) > MaxBatchRPCCalls {
+		RecordBatchSize(len(reqs))
+
+		if len(reqs) > s.maxBatchSize {
 			RecordRPCError(ctx, BackendProxyd, MethodUnknown, ErrTooManyBatchRequests)
 			writeRPCError(ctx, w, nil, ErrTooManyBatchRequests)
 			return
@@ -394,13 +398,8 @@ func (s *Server) handleBatchRPC(ctx context.Context, reqs []json.RawMessage, isL
 				"req_id", GetReqID(ctx),
 				"method", parsedReq.Method,
 			)
-			rpcErr := ErrOverRateLimit
-			if s.limConfig.ErrorMessage != "" {
-				rpcErr = rpcErr.Clone()
-				rpcErr.Message = s.limConfig.ErrorMessage
-			}
-			RecordRPCError(ctx, BackendProxyd, parsedReq.Method, rpcErr)
-			responses[i] = NewRPCErrorRes(parsedReq.ID, rpcErr)
+			RecordRPCError(ctx, BackendProxyd, parsedReq.Method, ErrOverRateLimit)
+			responses[i] = NewRPCErrorRes(parsedReq.ID, ErrOverRateLimit)
 			continue
 		}