diff --git a/batchbuilder/batchbuilder.go b/batchbuilder/batchbuilder.go
new file mode 100644
index 0000000..26b4e41
--- /dev/null
+++ b/batchbuilder/batchbuilder.go
@@ -0,0 +1,161 @@
+package batchbuilder
+
+import (
+	"math/big"
+
+	ethCommon "github.com/ethereum/go-ethereum/common"
+	"github.com/hermeznetwork/hermez-node/common"
+	"github.com/iden3/go-merkletree"
+	"github.com/iden3/go-merkletree/db"
+	"github.com/iden3/go-merkletree/db/memory"
+)
+
+type ConfigCircuit struct {
+	TxsMax       uint64
+	L1TxsMax     uint64
+	SMTLevelsMax uint64
+}
+
+type BatchBuilder struct {
+	StateDB        db.Storage // where the MTs will be stored by the Synchronizer
+	idx            uint64
+	mt             *merkletree.MerkleTree
+	configCircuits []ConfigCircuit
+}
+
+type ConfigBatch struct {
+	CoordinatorAddress ethCommon.Address
+}
+
+// NewBatchBuilder constructs a new BatchBuilder, and executes the bb.Reset
+// method
+func NewBatchBuilder(stateDB db.Storage, configCircuits []ConfigCircuit, batchNum int, idx, nLevels uint64) (*BatchBuilder, error) {
+	localMt, err := merkletree.NewMerkleTree(memory.NewMemoryStorage(), int(nLevels))
+	if err != nil {
+		return nil, err
+	}
+	bb := BatchBuilder{
+		StateDB:        stateDB,
+		idx:            idx,
+		mt:             localMt,
+		configCircuits: configCircuits,
+	}
+
+	bb.Reset(batchNum, idx, true)
+
+	return &bb, nil
+}
+
+// Reset tells the BatchBuilder to reset it's internal state to the required
+// `batchNum`.  If `fromSynchronizer` is true, the BatchBuilder must take a
+// copy of the rollup state from the Synchronizer at that `batchNum`, otherwise
+// it can just roll back the internal copy.
+func (bb *BatchBuilder) Reset(batchNum int, idx uint64, fromSynchronizer bool) error {
+
+	return nil
+}
+
+func (bb *BatchBuilder) BuildBatch(configBatch ConfigBatch, l1usertxs, l1coordinatortxs []common.L1Tx, l2txs []common.L2Tx, tokenIDs []common.TokenID) (*common.ZKInputs, error) {
+
+	for _, tx := range l1usertxs {
+		bb.processL1Tx(tx)
+	}
+	for _, tx := range l1coordinatortxs {
+		bb.processL1Tx(tx)
+	}
+	for _, tx := range l2txs {
+		switch tx.Type {
+		case common.TxTypeTransfer:
+			// go to the MT leaf of sender and receiver, and update
+			// balance & nonce
+			bb.applyTransfer(tx.Tx)
+		case common.TxTypeExit:
+			// execute exit flow
+		default:
+		}
+
+	}
+
+	return nil, nil
+}
+
+func (bb *BatchBuilder) processL1Tx(tx common.L1Tx) error {
+	switch tx.Type {
+	case common.TxTypeForceTransfer, common.TxTypeTransfer:
+		// go to the MT leaf of sender and receiver, and update balance
+		// & nonce
+		bb.applyTransfer(tx.Tx)
+	case common.TxTypeCreateAccountDeposit:
+		// add new leaf to the MT, update balance of the MT leaf
+		bb.applyCreateLeaf(tx)
+	case common.TxTypeDeposit:
+		// update balance of the MT leaf
+		bb.applyDeposit(tx)
+	case common.TxTypeDepositAndTransfer:
+		// update balance in MT leaf, update balance & nonce of sender
+		// & receiver
+		bb.applyDeposit(tx) // this after v0, can be done by bb.applyDepositAndTransfer in a single step
+		bb.applyTransfer(tx.Tx)
+	case common.TxTypeCreateAccountDepositAndTransfer:
+		// add new leaf to the merkletree, update balance in MT leaf,
+		// update balance & nonce of sender & receiver
+		bb.applyCreateLeaf(tx)
+		bb.applyTransfer(tx.Tx)
+	case common.TxTypeExit:
+		// execute exit flow
+	default:
+	}
+
+	return nil
+}
+
+// applyCreateLeaf creates a new leaf in the leaf of the depositer, it stores
+// the deposit value
+func (bb *BatchBuilder) applyCreateLeaf(tx common.L1Tx) error {
+	k := big.NewInt(int64(bb.idx + 1))
+
+	leaf := common.Leaf{
+		TokenID: tx.TokenID,
+		Nonce:   0, // TODO check always that a new leaf is created nonce is at 0
+		Balance: tx.LoadAmount,
+		Ax:      tx.FromBJJ.X,
+		Ay:      tx.FromBJJ.Y,
+		EthAddr: tx.FromEthAddr,
+	}
+
+	v, err := leaf.Value()
+	if err != nil {
+		return err
+	}
+
+	// store at the DB the key: v, and value: leaf.Bytes()
+	dbTx, err := bb.mt.DB().NewTx()
+	if err != nil {
+		return err
+	}
+	leafBytes := leaf.Bytes()
+	dbTx.Put(v.Bytes(), leafBytes[:])
+
+	// Add k & v into the MT
+	err = bb.mt.Add(k, v)
+	if err != nil {
+		return err
+	}
+
+	// if everything is fine, increment idx
+	bb.idx = bb.idx + 1
+	return nil
+}
+
+// applyDeposit updates the balance in the leaf of the depositer
+func (bb *BatchBuilder) applyDeposit(tx common.L1Tx) error {
+
+	return nil
+}
+
+// applyTransfer updates the balance & nonce in the leaf of the sender, and the
+// balance in the leaf of the receiver
+func (bb *BatchBuilder) applyTransfer(tx common.Tx) error {
+
+	return nil
+}
diff --git a/batchbuilder/batchbuilder_test.go b/batchbuilder/batchbuilder_test.go
new file mode 100644
index 0000000..b8fd379
--- /dev/null
+++ b/batchbuilder/batchbuilder_test.go
@@ -0,0 +1,18 @@
+package batchbuilder
+
+import (
+	"fmt"
+	"testing"
+
+	"github.com/iden3/go-merkletree/db/memory"
+	"github.com/stretchr/testify/assert"
+)
+
+func TestBatchBuilder(t *testing.T) {
+
+	stateDB := memory.NewMemoryStorage()
+
+	bb, err := NewBatchBuilder(stateDB, nil, 0, 0, 32)
+	assert.Nil(t, err)
+	fmt.Println(bb)
+}
diff --git a/common/leaf.go b/common/leaf.go
index 9cb4e73..7bf60d6 100644
--- a/common/leaf.go
+++ b/common/leaf.go
@@ -8,6 +8,7 @@ import (
 	"math/big"
 
 	eth "github.com/ethereum/go-ethereum/common"
+	"github.com/iden3/go-iden3-crypto/poseidon"
 	cryptoUtils "github.com/iden3/go-iden3-crypto/utils"
 )
 
@@ -65,6 +66,16 @@ func (l *Leaf) BigInts() ([5]*big.Int, error) {
 	return e, nil
 }
 
+// Value returns the value of the Leaf, which is the Poseidon hash of its *big.Int representation
+func (l *Leaf) Value() (*big.Int, error) {
+	toHash := [poseidon.T]*big.Int{}
+	lBI := l.BigInts()
+	copy(toHash[:], lBI[:])
+
+	v, err := poseidon.Hash(toHash)
+	return v, err
+}
+
 // LeafFromBigInts returns a Leaf from a [5]*big.Int
 func LeafFromBigInts(e [5]*big.Int) (*Leaf, error) {
 	if !cryptoUtils.CheckBigIntArrayInField(e[:]) {
diff --git a/go.mod b/go.mod
index 1425a09..584e13f 100644
--- a/go.mod
+++ b/go.mod
@@ -3,6 +3,7 @@ module github.com/hermeznetwork/hermez-node
 go 1.14
 
 require (
+	github.com/dghubble/sling v1.3.0
 	github.com/ethereum/go-ethereum v1.9.17
 	github.com/iden3/go-iden3-crypto v0.0.6-0.20200723082457-29a66457f0bf
 	github.com/iden3/go-merkletree v0.0.0-20200723202738-75e24244a1e3
diff --git a/go.sum b/go.sum
index 76132c8..977471c 100644
--- a/go.sum
+++ b/go.sum
@@ -62,6 +62,7 @@ github.com/deckarep/golang-set v0.0.0-20180603214616-504e848d77ea/go.mod h1:93vs
 github.com/deckarep/golang-set v1.7.1/go.mod h1:93vsz/8Wt4joVM7c2AVqh+YRMiUSc14yDtF28KmMOgQ=
 github.com/denisenkom/go-mssqldb v0.0.0-20191124224453-732737034ffd h1:83Wprp6ROGeiHFAP8WJdI2RoxALQYgdllERc3N5N2DM=
 github.com/denisenkom/go-mssqldb v0.0.0-20191124224453-732737034ffd/go.mod h1:xbL0rPBG9cCiLr28tMa8zpbdarY27NDyej4t/EjAShU=
+github.com/dghubble/sling v1.3.0 h1:pZHjCJq4zJvc6qVQ5wN1jo5oNZlNE0+8T/h0XeXBUKU=
 github.com/dghubble/sling v1.3.0/go.mod h1:XXShWaBWKzNLhu2OxikSNFrlsvowtz4kyRuXUG7oQKY=
 github.com/dgrijalva/jwt-go v3.2.0+incompatible/go.mod h1:E3ru+11k8xSBh+hMPgOLZmtrrCbhqsmaPHjLKYnJCaQ=
 github.com/dgryski/go-sip13 v0.0.0-20181026042036-e10d5fee7954/go.mod h1:vAd38F8PWV+bWy6jNmig1y/TA+kYO4g3RSRF0IAv0no=
@@ -111,6 +112,7 @@ github.com/golang/snappy v0.0.1/go.mod h1:/XxbfmMg8lxefKM7IXC3fBNl/7bRcc72aCRzEW
 github.com/golang/snappy v0.0.2-0.20200707131729-196ae77b8a26/go.mod h1:/XxbfmMg8lxefKM7IXC3fBNl/7bRcc72aCRzEWrmP2Q=
 github.com/google/go-cmp v0.3.0/go.mod h1:8QqcDgzrUqlUb/G2PQTWiueGozuR1884gddMywk6iLU=
 github.com/google/go-cmp v0.3.1/go.mod h1:8QqcDgzrUqlUb/G2PQTWiueGozuR1884gddMywk6iLU=
+github.com/google/go-querystring v1.0.0 h1:Xkwi/a1rcvNg1PPYe5vI8GbeBY/jrVuDX5ASuANWTrk=
 github.com/google/go-querystring v1.0.0/go.mod h1:odCYkC5MyYFN7vkCjXpyrEuKhc/BUO6wN/zVPAxq5ck=
 github.com/google/uuid v1.0.0/go.mod h1:TIyPZe4MgqvfeYDBFedMoGGpEw/LqOeaOT+nhxU+yHo=
 github.com/gorilla/websocket v1.4.1-0.20190629185528-ae1634f6a989/go.mod h1:E7qHFY5m1UJ88s3WnNqhKjPHQ0heANvMoAMk2YaljkQ=