diff --git a/README.md b/README.md
index 882b8b2e3..2eee7ff53 100644
--- a/README.md
+++ b/README.md
@@ -35,8 +35,8 @@ Documentation: <https://shopify.github.io/liquid/basics/introduction/#tags>
 - [ ] tablerow [Document: cols,limit,offset,range](https://shopify.github.io/liquid/tags/iteration/) [Source](https://github.com/harttle/shopify-liquid/blob/master/tags/.js) [Test][tt]
 - [x] assign [Document](https://shopify.github.io/liquid/tags/variable/) [Source](https://github.com/harttle/shopify-liquid/blob/master/tags/assign.js) [Test][tt]
 - [x] capture [Document](https://shopify.github.io/liquid/tags/variable/) [Source](https://github.com/harttle/shopify-liquid/blob/master/tags/.js) [Test][tt]
-- [ ] increment [Document](https://shopify.github.io/liquid/tags/variable/) [Source](https://github.com/harttle/shopify-liquid/blob/master/tags/.js) [Test][tt]
-- [ ] decrement [Document](https://shopify.github.io/liquid/tags/variable/) [Source](https://github.com/harttle/shopify-liquid/blob/master/tags/.js) [Test][tt]
+- [x] increment [Document](https://shopify.github.io/liquid/tags/variable/) [Source](https://github.com/harttle/shopify-liquid/blob/master/tags/.js) [Test][tt]
+- [x] decrement [Document](https://shopify.github.io/liquid/tags/variable/) [Source](https://github.com/harttle/shopify-liquid/blob/master/tags/.js) [Test][tt]
 
 
 ## Filters
diff --git a/error.js b/error.js
new file mode 100644
index 000000000..f4ba888ce
--- /dev/null
+++ b/error.js
@@ -0,0 +1,11 @@
+
+function factory(msg, token){
+    var err = new Error(msg || 'unkown error');
+    if(token){
+        err.token = token.raw;
+        err.line = token.line;
+    }
+    throw err;
+}
+
+module.exports = factory;
diff --git a/filter.js b/filter.js
index bb3eaf652..08626eec1 100644
--- a/filter.js
+++ b/filter.js
@@ -14,12 +14,9 @@ module.exports = function() {
 
     function construct(str) {
         var match = lexical.filterLine.exec(str.trim());
-        if (!match) {
-            throw new Error('illegal filter: ' + str);
-        }
-        var k = match[1],
-            v = match[2];
+        if (!match) error('illegal filter: ' + str);
 
+        var k = match[1], v = match[2];
         return factory(k, [v]);
     }
 
diff --git a/index.js b/index.js
index db2a104cf..e96e2d68f 100644
--- a/index.js
+++ b/index.js
@@ -6,6 +6,7 @@ const path = require("path");
 const fs = require('fs');
 const Tag = require('./tag.js');
 const Filter = require('./filter.js');
+const error = require('./error.js');
 
 const tagsPath = path.join(__dirname, "tags");
 const filtersPath = path.join(__dirname, "filters");
@@ -45,5 +46,6 @@ function factory(){
 }
 
 factory.lexical = lexical;
+factory.error = error;
 
 module.exports = factory;
diff --git a/package.json b/package.json
index a89b6e25e..36ad548f9 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "shopify-liquid",
-  "version": "1.0.1",
+  "version": "1.0.2",
   "description": "A Shopify Liquid Implementation in Node.js",
   "main": "index.js",
   "scripts": {
@@ -21,7 +21,8 @@
   },
   "homepage": "https://github.com/harttle/shopify-liquid#readme",
   "dependencies": {
-    "lodash": "^4.13.1"
+    "lodash": "^4.13.1",
+    "strftime": "^0.9.2"
   },
   "devDependencies": {
     "chai": "^3.5.0",
diff --git a/render.js b/render.js
index feed49490..731f3260e 100644
--- a/render.js
+++ b/render.js
@@ -1,5 +1,6 @@
 const lexical = require('./lexical.js');
 const syntax = require('./syntax.js');
+const error = require('./error.js');
 
 module.exports = function(Filter, Tag) {
     function render(tokens, scope) {
@@ -17,14 +18,14 @@ module.exports = function(Filter, Tag) {
                     html += renderTag(token, tokens, scope);
                     break;
                 default:
-                    throw new Error(`unexpected type: ${token.type}`);
+                    error(`unexpected type: ${token.type}`, token);
             }
         }
         return html;
     }
 
     function evalExp(exp, scope) {
-        if(!scope) throw new Error('unable to evalExp: scope undefined');
+        if(!scope) error('unable to evalExp: scope undefined');
         var operatorREs = lexical.operators;
         for (var i = 0; i < operatorREs.length; i++) {
             var operatorRE = operatorREs[i];
@@ -41,7 +42,7 @@ module.exports = function(Filter, Tag) {
     }
 
     function evalFilter(str, scope){
-        if(!scope) throw new Error('unable to evalFilter: scope undefined');
+        if(!scope) error('unable to evalFilter: scope undefined');
         var filters = str.split('|');
         var val = scope.get(filters.shift());
         return filters
@@ -57,9 +58,7 @@ module.exports = function(Filter, Tag) {
             while ((curToken = tokens.shift()) && curToken.value !== endToken) {
                 subTokens.push(curToken);
             }
-            if (!curToken) {
-                throw new Error(`${token.value} not closed`);
-            }
+            if (!curToken) error(`${token.value} not closed`);
         }
         return tag.render(subTokens, scope);
     }
diff --git a/tags/assign.js b/tags/assign.js
index 1d485d1c3..f31a32771 100644
--- a/tags/assign.js
+++ b/tags/assign.js
@@ -6,7 +6,7 @@ module.exports = function(liquid) {
 
     liquid.registerTag('assign', {
         render: function(tokens, scope, token, hash) {
-            var match = token.value.match(re);
+            var match = token.args.match(re);
             var k = match[1], v = match[2];
             scope.set(k, liquid.evaluate(v, scope));
         }
diff --git a/tags/decrement.js b/tags/decrement.js
new file mode 100644
index 000000000..e8eea2ee6
--- /dev/null
+++ b/tags/decrement.js
@@ -0,0 +1,17 @@
+const Liquid = require('..');
+const lexical = Liquid.lexical;
+const error = Liquid.error;
+
+module.exports = function(liquid) {
+
+    liquid.registerTag('decrement', {
+        render: function(tokens, scope, token, hash) {
+            var match = token.args.match(lexical.identifier);
+            if(!match) error(`illegal identifier ${token.args}`, token);
+            var k = match[0], v = scope.get(k);
+            if(typeof v !== 'number') v = 0;
+            scope.set(k, v-1);
+        }
+    });
+
+};
diff --git a/tags/increment.js b/tags/increment.js
new file mode 100644
index 000000000..f3bdeb6b6
--- /dev/null
+++ b/tags/increment.js
@@ -0,0 +1,17 @@
+const Liquid = require('..');
+const lexical = Liquid.lexical;
+const error = Liquid.error;
+
+module.exports = function(liquid) {
+
+    liquid.registerTag('increment', {
+        render: function(tokens, scope, token, hash) {
+            var match = token.args.match(lexical.identifier);
+            if(!match) error(`illegal identifier ${token.args}`, token);
+            var k = match[0], v = scope.get(k);
+            if(typeof v !== 'number') v = 0;
+            scope.set(k, v+1);
+        }
+    });
+
+};
diff --git a/test/tags.js b/test/tags.js
index 88062370c..111cd8e8d 100644
--- a/test/tags.js
+++ b/test/tags.js
@@ -1,18 +1,20 @@
 const chai = require("chai");
 const expect = chai.expect;
 
-var liquid = require('..')();
-
-var ctx = {
-    one: 1,
-    two: 2,
-    leq: '<=',
-    empty: '',
-    foo: 'bar',
-    arr: [-2, 'a']
-};
+var liquid = require('..')(),
+    ctx;
 
 describe('tags', function() {
+    beforeEach(function() {
+        ctx = {
+            one: 1,
+            two: 2,
+            leq: '<=',
+            empty: '',
+            foo: 'bar',
+            arr: [-2, 'a']
+        };
+    });
     it('should support assign', function() {
         expect(liquid.render('{% assign foo="bar"%}{{foo}}', ctx)).to.equal('bar');
     });
@@ -34,22 +36,31 @@ describe('tags', function() {
             '{%endcase%}')).to.equal('d');
     });
 
-    it('should support if', function(){
+    it('should support if', function() {
         expect(liquid.render('{% if 2==3 %}yes{%else%}no{%endif%}', ctx)).to.equal('no');
         expect(liquid.render('{% if 1==2 and one<two %}a{%endif%}', ctx)).to.equal('');
         expect(liquid.render('{% if false %}yes{%else%}no{%endif%}', ctx)).to.equal('no');
     });
 
-    it('should support unless', function(){
+    it('should support unless', function() {
         expect(liquid.render('{% unless 1 %}yes{%else%}no{%endunless%}', ctx)).to.equal('no');
         expect(liquid.render('{% unless 1>2 %}yes{%endunless%}', ctx)).to.equal('yes');
     });
 
-    it('should support capture', function(){
+    it('should support capture', function() {
         expect(liquid.render('{% capture f %}{{"a" | capitalize}}{%endcapture%}{{f}}', ctx)).to.equal('A');
-        expect(function(){
+        expect(function() {
             liquid.render('{% capture = %}{%endcapture%}', ctx);
         }).to.throw(/= not valid identifier/);
     });
-});
 
+    it('should support increment', function() {
+        expect(liquid.render('{% increment foo %}{%increment foo%}{{foo}}', ctx)).to.equal('2');
+        expect(liquid.render('{% increment one %}{{one}}', ctx)).to.equal('2');
+    });
+
+    it('should support decrement', function() {
+        expect(liquid.render('{% decrement foo %}{%decrement foo%}{{foo}}', ctx)).to.equal('-2');
+        expect(liquid.render('{% decrement one %}{{one}}', ctx)).to.equal('0');
+    });
+});
diff --git a/tokenizer.js b/tokenizer.js
index 36157201c..d4d30de1d 100644
--- a/tokenizer.js
+++ b/tokenizer.js
@@ -1,11 +1,12 @@
 const lexical = require('./lexical.js');
+const error = require('./error.js');
 
 function parse(html){
     var tokens = [];
     if(!html) return tokens;
 
     var syntax = /({%(.*?)%})|({{(.*?)}})/g;
-    var result, htmlFragment;
+    var result, htmlFragment, token;
     var idx = 0;
 
     while ((result = syntax.exec(html)) !== null) {
@@ -16,29 +17,19 @@ function parse(html){
                 value: htmlFragment
             });
         }
-        var rawTag = result[1],
-            cleanTag = result[2],
-            rawOut = result[3],
-            cleanOut = result[4];
 
-        if(rawTag){
-            var match = cleanTag.trim().match(lexical.tagLine);
-            if (!match) throw new Error('illegal tag: ' + rawTag);
-            var name = match[1], args = match[2];
+        if(result[1]){
+            token = factory('tag', 1, result);
+            var match = token.value.match(lexical.tagLine);
+            if (!match) error('illegal tag', token);
 
-            tokens.push({
-                type: 'tag',
-                value: cleanTag.trim(),
-                raw: rawTag,
-                args, name
-            });
+            token.name = match[1];
+            token.args = match[2];
+            tokens.push(token);
         }
         else{
-            tokens.push({
-                type: 'output',
-                raw: rawOut,
-                value: cleanOut.trim()
-            });
+            token = factory('output', 3, result);
+            tokens.push(token);
         }
         idx = syntax.lastIndex;
     }
@@ -51,6 +42,24 @@ function parse(html){
         });
     }
     return tokens;
+
+    function factory(type, offset, match){
+        var token = {
+            type,
+            raw: match[offset],
+            value: match[offset + 1].trim(),
+            line: crCount(match.index) + 1
+        };
+        return token;
+    }
+
+    var lastIdx = -1;
+    var lastCount = 0;
+    function crCount(idx){
+        lastCount += html.slice(lastIdx+1, idx);
+        lastIdx = idx;
+        return lastCount;
+    }
 }
 
 exports.parse = parse;