diff --git a/lib/clienterror.js b/lib/clienterror.js
new file mode 100644
index 0000000..2e6fd84
--- /dev/null
+++ b/lib/clienterror.js
@@ -0,0 +1,21 @@
+function ClientError() {
+  var args = Array.prototype.slice.call(arguments);
+
+  switch (args.length) {
+    case 0:
+      this.code = 'BADREQUEST';
+      this.message = 'Bad request';
+      break;
+    case 1:
+      this.code = 'BADREQUEST';
+      this.message = args[0];
+      break;
+    default:
+    case 2:
+      this.code = args[0];
+      this.message = args[1];
+      break;
+  }
+};
+
+module.exports = ClientError;
diff --git a/lib/server.js b/lib/server.js
index 511635f..edf7834 100644
--- a/lib/server.js
+++ b/lib/server.js
@@ -13,6 +13,7 @@ var PublicKey = Bitcore.PublicKey;
 var HDPublicKey = Bitcore.HDPublicKey;
 var Explorers = require('bitcore-explorers');
 
+var ClientError = require('./clienterror');
 var Utils = require('./utils');
 var Storage = require('./storage');
 var SignUtils = require('./signutils');
@@ -57,9 +58,9 @@ CopayServer.prototype.createWallet = function(opts, cb) {
     pubKey;
 
   Utils.checkRequired(opts, ['id', 'name', 'm', 'n', 'pubKey']);
-  if (!Wallet.verifyCopayerLimits(opts.m, opts.n)) return cb('Invalid m/n combination');
+  if (!Wallet.verifyCopayerLimits(opts.m, opts.n)) return cb(new ClientError('Invalid combination of required copayers / total copayers'));
   var network = opts.network || 'livenet';
-  if (network != 'livenet' && network != 'testnet') return cb('Invalid network');
+  if (network != 'livenet' && network != 'testnet') return cb(new ClientError('Invalid network'));
 
   try {
     pubKey = new PublicKey.fromString(opts.pubKey);
@@ -69,7 +70,7 @@ CopayServer.prototype.createWallet = function(opts, cb) {
 
   self.storage.fetchWallet(opts.id, function(err, wallet) {
     if (err) return cb(err);
-    if (wallet) return cb('Wallet already exists');
+    if (wallet) return cb(new ClientError('WEXISTS', 'Wallet already exists'));
 
     var wallet = new Wallet({
       id: opts.id,
@@ -95,7 +96,7 @@ CopayServer.prototype.getWallet = function(opts, cb) {
 
   self.storage.fetchWallet(opts.id, function(err, wallet) {
     if (err) return cb(err);
-    if (!wallet) return cb('Wallet not found');
+    if (!wallet) return cb(new ClientError('Wallet not found'));
     return cb(null, wallet);
   });
 };
@@ -132,13 +133,13 @@ CopayServer.prototype.joinWallet = function(opts, cb) {
       if (err) return cb(err);
 
       if (!self._verifySignature(opts.xPubKey, opts.xPubKeySignature, wallet.pubKey)) {
-        return cb('Bad request');
+        return cb(new ClientError());
       }
 
       if (_.find(wallet.copayers, {
         xPubKey: opts.xPubKey
-      })) return cb('Copayer already in wallet');
-      if (wallet.copayers.length == wallet.n) return cb('Wallet full');
+      })) return cb(new ClientError('CINWALLET', 'Copayer already in wallet'));
+      if (wallet.copayers.length == wallet.n) return cb(new ClientError('WFULL', 'Wallet full'));
 
       var copayer = new Copayer({
         id: opts.id,
@@ -234,7 +235,7 @@ CopayServer.prototype.verifyMessageSignature = function(opts, cb) {
     if (err) return cb(err);
 
     var copayer = wallet.getCopayer(opts.copayerId);
-    if (!copayer) return cb('Copayer not found');
+    if (!copayer) return cb(new ClientError('Copayer not found'));
 
     var isValid = self._verifySignature(opts.message, opts.signature, copayer.signingPubKey);
     return cb(null, isValid);
@@ -268,7 +269,7 @@ CopayServer.prototype._getUtxos = function(opts, cb) {
   // Get addresses for this wallet
   self.storage.fetchAddresses(opts.walletId, function(err, addresses) {
     if (err) return cb(err);
-    if (addresses.length == 0) return cb('The wallet has no addresses');
+    if (addresses.length == 0) return cb(new ClientError('The wallet has no addresses'));
 
     var addresses = _.pluck(addresses, 'address');
 
@@ -417,8 +418,9 @@ CopayServer.prototype.createTx = function(opts, cb) {
       });
 
       txp.inputs = self._selectUtxos(txp, utxos);
-      if (!txp.inputs)
-        return cb('insufficient funds')
+      if (!txp.inputs) {
+        return cb(new ClientError('INSUFFICIENTFUNDS', 'Insufficient funds'));
+      }
 
       // no need to do this now: // TODO remove this comment
       //self._createRawTx(txp);
@@ -453,12 +455,12 @@ CopayServer.prototype.signTx = function(opts, cb) {
 
   self.fetchTx(opts.walletId, opts.txProposalId, function(err, txp) {
     if (err) return cb(err);
-    if (!txp) return cb('Transaction proposal not found');
+    if (!txp) return cb(new ClientError('Transaction proposal not found'));
     var action = _.find(txp.actions, {
       copayerId: opts.copayerId
     });
-    if (action) return cb('Copayer already voted on this transaction proposal');
-    if (txp.status != 'pending') return cb('The transaction proposal is not pending');
+    if (action) return cb(new ClientError('CVOTED', 'Copayer already voted on this transaction proposal'));
+    if (txp.status != 'pending') return cb(new ClientError('TXNOTPENDING', 'The transaction proposal is not pending'));
 
     txp.sign(opts.copayerId, opts.signature);
 
@@ -495,12 +497,12 @@ CopayServer.prototype.rejectTx = function(opts, cb) {
 
   self.fetchTx(opts.walletId, opts.txProposalId, function(err, txp) {
     if (err) return cb(err);
-    if (!txp) return cb('Transaction proposal not found');
+    if (!txp) return cb(new ClientError('Transaction proposal not found'));
     var action = _.find(txp.actions, {
       copayerId: opts.copayerId
     });
-    if (action) return cb('Copayer already voted on this transaction proposal');
-    if (txp.status != 'pending') return cb('The transaction proposal is not pending');
+    if (action) return cb(new ClientError('CVOTED', 'Copayer already voted on this transaction proposal'));
+    if (txp.status != 'pending') return cb(new ClientError('TXNOTPENDING', 'The transaction proposal is not pending'));
 
     txp.reject(opts.copayerId);
 
diff --git a/test/integration.js b/test/integration.js
index 03f1640..d631f98 100644
--- a/test/integration.js
+++ b/test/integration.js
@@ -218,7 +218,7 @@ describe('Copay server', function() {
         id: '345'
       }, function(err, wallet) {
         should.exist(err);
-        err.should.equal('Wallet not found');
+        err.message.should.equal('Wallet not found');
         done();
       });
     });
@@ -306,7 +306,7 @@ describe('Copay server', function() {
         opts.n = pair.n;
         server.createWallet(opts, function(err) {
           should.exist(err);
-          err.should.contain('Invalid m/n combination');
+          err.message.should.equal('Invalid combination of required copayers / total copayers');
           return cb();
         });
       }, function(err) {
@@ -413,7 +413,8 @@ describe('Copay server', function() {
             wallet.status.should.equal('complete');
             server.joinWallet(copayer2Opts, function(err) {
               should.exist(err);
-              err.should.equal('Wallet full');
+              err.code.should.equal('WFULL');
+              err.message.should.equal('Wallet full');
               done();
             });
           });
@@ -442,7 +443,8 @@ describe('Copay server', function() {
           should.not.exist(err);
           server.joinWallet(copayerOpts, function(err) {
             should.exist(err);
-            err.should.equal('Copayer already in wallet');
+            err.code.should.equal('CINWALLET');
+            err.message.should.equal('Copayer already in wallet');
             done();
           });
         });
@@ -468,7 +470,7 @@ describe('Copay server', function() {
           xPubKeySignature: 'bad sign',
         };
         server.joinWallet(copayerOpts, function(err) {
-          err.should.contain('Bad request');
+          err.message.should.equal('Bad request');
           done();
         });
       });
@@ -518,7 +520,7 @@ describe('Copay server', function() {
           xPubKeySignature: someXPubKeysSignatures[0],
         };
         server.joinWallet(copayerOpts, function(err) {
-          err.should.contain('Bad request');
+          err.message.should.equal('Bad request');
           done();
         });
       });
@@ -571,7 +573,7 @@ describe('Copay server', function() {
           signature: 'dummy',
         };
         server.verifyMessageSignature(opts, function(err, isValid) {
-          err.should.equal('Copayer not found');
+          err.message.should.equal('Copayer not found');
           done();
         });
       });
@@ -776,7 +778,8 @@ describe('Copay server', function() {
         };
 
         server.createTx(txOpts, function(err, tx) {
-          err.should.contain('insufficient');
+          err.code.should.equal('INSUFFICIENTFUNDS');
+          err.message.should.equal('Insufficient funds');
           server.getPendingTxs({
             walletId: '123'
           }, function(err, txs) {
@@ -877,7 +880,8 @@ describe('Copay server', function() {
             requestSignature: 'dummy',
           };
           server.createTx(txOpts2, function(err, tx) {
-            err.should.contain('insufficient');
+            err.code.should.equal('INSUFFICIENTFUNDS');
+            err.message.should.equal('Insufficient funds');
             should.not.exist(tx);
             server.getPendingTxs({
               walletId: '123'