diff --git a/package.json b/package.json
index 72f0d9b..a48689e 100644
--- a/package.json
+++ b/package.json
@@ -24,6 +24,8 @@
   "dependencies": {
     "babel-runtime": "^5.4.4",
     "emit-then": "^1.0.2",
+    "event-promise": "0.0.1",
+    "flatmap": "0.0.3",
     "minecraft-data": "0.7.0",
     "minecraft-protocol": "0.16.3",
     "mkdirp": "0.5.1",
@@ -38,11 +40,11 @@
     "prismarine-world": "0.3.3",
     "prismarine-world-sync": "0.1.0",
     "random-seed": "^0.2.0",
+    "range": "0.0.3",
     "request-promise": "^0.4.3",
     "requireindex": "~1.0.0",
     "spiralloop": "1.0.2",
-    "vec3": "0.1.3",
-    "event-promise": "0.0.1"
+    "vec3": "0.1.3"
   },
   "license": "MIT",
   "repository": {
diff --git a/src/index.js b/src/index.js
index 87a4874..65e1a30 100644
--- a/src/index.js
+++ b/src/index.js
@@ -14,7 +14,8 @@ module.exports = {
   version:require("./lib/version"),
   generations:require("./lib/generations"),
   experience:require("./lib/experience"),
-  UserError:require("./lib/user_error")
+  UserError:require("./lib/user_error"),
+  portal_detector:require('./lib/portal_detector')
 };
 
 function createMCServer(options) {
diff --git a/src/lib/plugins/useItem.js b/src/lib/plugins/useItem.js
new file mode 100644
index 0000000..28be69d
--- /dev/null
+++ b/src/lib/plugins/useItem.js
@@ -0,0 +1,30 @@
+var items=require("minecraft-data")(require("flying-squid").version).items;
+var Vec3 = require("vec3").Vec3;
+var {detectFrame,getAir}=require("flying-squid").portal_detector;
+
+module.exports.player=function(player,serv)
+{
+  player._client.on("block_place",({direction,heldItem,location} = {}) => {
+    if (direction == -1 || heldItem.blockId == -1 || !items[heldItem.blockId]) return;
+    var referencePosition = new Vec3(location.x, location.y, location.z);
+    var directionVector = directionToVector[direction];
+    var position = referencePosition.plus(directionVector);
+
+    var item= items[heldItem.blockId];
+    if(item.name=="flint_and_steel")
+      player.use_flint_and_steel(referencePosition,directionVector);
+  });
+
+  player.use_flint_and_steel=async (referencePosition,direction) => {
+    let block=await player.world.getBlock(referencePosition);
+    if(block.name=="obsidian")
+    {
+      var frames=await detectFrame(player.world,referencePosition,direction);
+      if(frames.length==0)
+        return;
+      var air=getAir(frames[0]);
+      air.forEach(pos => player.setBlock(pos,90,(frames[0].bottom[0].x-frames[0].bottom[1].x)!=0 ? 1 : 2));
+    }
+  };
+};
+var directionToVector=[new Vec3(0,-1,0),new Vec3(0,1,0),new Vec3(0,0,-1),new Vec3(0,0,1),new Vec3(-1,0,0),new Vec3(1,0,0)];
\ No newline at end of file
diff --git a/src/lib/portal_detector.js b/src/lib/portal_detector.js
new file mode 100644
index 0000000..b4535ea
--- /dev/null
+++ b/src/lib/portal_detector.js
@@ -0,0 +1,108 @@
+var Vec3 = require("vec3").Vec3;
+var assert = require('assert');
+var flatMap = require('flatmap');
+var range = require('range').range;
+
+module.exports={detectFrame,findPotentialLines,findBorder,getAir};
+
+async function findLineInDirection(world,startingPoint,type,direction,directionV)
+{
+  var line=[];
+  var point=startingPoint;
+  while((await world.getBlock(point)).name==type && (await world.getBlockType(point.plus(directionV)))==0)
+  {
+    line.push(point);
+    point=point.plus(direction);
+  }
+  return line;
+}
+
+async function findLine(world,startingPoint,type,direction,directionV)
+{
+  var firstSegment=(await findLineInDirection(world,startingPoint.plus(direction.scaled(-1)),type,direction.scaled(-1),directionV)).reverse();
+  var secondSegment=await findLineInDirection(world,startingPoint,type,direction,directionV);
+  return firstSegment.concat(secondSegment);
+}
+
+
+async function findPotentialLines(world,startingPoint,directionV)
+{
+  var firstLineDirection=directionV.y!=0 ? [new Vec3(1,0,0),new Vec3(0,0,1)] :
+    [new Vec3(0,1,0)];
+  return (await Promise.all(firstLineDirection
+    .map(async d => ({direction:d,line:(await findLine(world,startingPoint,'obsidian',d,directionV))}))))
+    .filter(line => (line.line.length>=3 && line.direction.y!=0) ||
+    (line.line.length>=2 && line.direction.y==0));
+}
+
+function positiveOrder(line,direction)
+{
+  if(direction.x==-1 || direction.y==-1 || direction.z==-1)
+    return line.reverse();
+  return line;
+}
+
+async function findBorder(world,{line,direction},directionV)
+{
+  var bottom=line;
+  if(bottom.length==0)
+    return [];
+  var left=await findLineInDirection(world,bottom[0].plus(direction.scaled(-1).plus(directionV)),'obsidian',directionV,direction);
+  var right=await findLineInDirection(world,bottom[line.length-1].plus(direction).plus(directionV),'obsidian',
+    directionV,direction.scaled(-1));
+  if(left.length==0 || left.length!=right.length)
+    return null;
+  var top=await findLineInDirection(world,left[left.length-1].plus(direction).plus(directionV),'obsidian',
+    direction,directionV.scaled(-1));
+  if(bottom.length!=top.length)
+    return null;
+
+  left=positiveOrder(left,directionV);
+  right=positiveOrder(right,directionV);
+  top=positiveOrder(top,direction);
+
+
+  if(direction.y!=0)
+    [bottom,left,right,top]=[left,bottom,top,right];
+
+  [bottom,top]=directionV.y<0 ? [top,bottom] : [bottom,top];
+  var horDir=direction.x!=0 || directionV.x!=0 ? 'x' :'z';
+  [left,right]=direction[horDir]<0 || directionV[horDir]<0 ? [right,left] : [left,right];
+
+  if(bottom.length<2 || top.length<2 || left.length<3 || right.length<3)
+    return null;
+
+  return {bottom,left,right,top};
+}
+
+async function detectFrame(world,startingPoint,directionV)
+{
+  let potentialLines=await findPotentialLines(world,startingPoint,directionV);
+
+  return asyncFilter((await Promise.all(potentialLines
+    .map(line => findBorder(world,line,directionV))))
+    .filter(border => border!=null)
+    .map(({bottom,left,right,top}) => ({bottom,left,right,top,air:getAir({bottom,left,right,top})})),
+    async ({air}) => await isAllAir(world,air));
+}
+
+async function asyncEvery(array,pred) {
+  return Promise.all(array.map(x => pred(x).then(y => y ? true : Promise.reject(false))))
+    .then(results => true)
+    .catch(x => false);
+}
+
+function asyncFilter(array,pred) {
+  return Promise.all(array.map(e => pred(e).then(a => a ? e : null))).then(r => r.filter(a => a!=null));
+}
+
+async function isAllAir(world,blocks)
+{
+  return asyncEvery(blocks,async block => (await world.getBlockType(block))==0);
+}
+
+function getAir(border)
+{
+  var {bottom,top}=border;
+  return flatMap(bottom,pos => range(1,top[0].y-bottom[0].y).map(i => pos.offset(0,i,0)));
+}
\ No newline at end of file
diff --git a/test/portal_detector.js b/test/portal_detector.js
new file mode 100644
index 0000000..d22ade2
--- /dev/null
+++ b/test/portal_detector.js
@@ -0,0 +1,271 @@
+var {detectFrame,findPotentialLines,findBorder,getAir}=require("flying-squid").portal_detector;
+var World = require('prismarine-world');
+var Chunk = require('prismarine-chunk')(require("flying-squid").version);
+var Vec3 = require("vec3").Vec3;
+var assert = require('chai').assert;
+var range = require('range').range;
+var flatMap = require('flatmap');
+
+function generateLine(startingPoint,direction,length) {
+  return range(0,length).map(i => startingPoint.plus(direction.scaled(i)));
+}
+
+function generatePortal(bottomLeft,direction,width,height){
+  var directionV=new Vec3(0,1,0);
+  return {
+    bottom:generateLine(bottomLeft.plus(direction),direction,width-2),
+    left:generateLine(bottomLeft.plus(directionV),directionV,height-2),
+    right:generateLine(bottomLeft.plus(direction.scaled(width-1)).plus(directionV),directionV,height-2),
+    top:generateLine(bottomLeft.plus(directionV.scaled(height-1).plus(direction)),direction,width-2),
+    air:flatMap(generateLine(bottomLeft.plus(direction).plus(directionV),direction,width-2),
+      p => generateLine(p,directionV,height-2))
+  }
+}
+
+
+async function makeWorldWithPortal(portal,additionalAir,additionalObsidian)
+{
+  var {bottom,left,right,top,air}=portal;
+  var world=new World();
+  var chunk=new Chunk();
+
+  [bottom,left,right,top].forEach(border => border.forEach(pos => chunk.setBlockType(pos,49)));
+  air.forEach(pos => chunk.setBlockType(pos,0));
+
+  additionalAir.forEach(pos => chunk.setBlockType(pos,0));
+  additionalObsidian.forEach(pos => chunk.setBlockType(pos,49));
+
+
+  await world.setColumn(0,0,chunk);
+  return world;
+}
+
+describe("Generate portal",function(){
+  it("generate a line",() => {
+    assert.deepEqual(generateLine(new Vec3(3,1,1),new Vec3(1,0,0),2),[new Vec3(3, 1, 1), new Vec3(4, 1, 1)])
+  });
+  it("generate a portal", () => {
+    assert.deepEqual(generatePortal(new Vec3(2,1,1),new Vec3(1,0,0),4,5),{
+      bottom:generateLine(new Vec3(3,1,1),new Vec3(1,0,0),2),
+      left:generateLine(new Vec3(2,2,1),new Vec3(0,1,0),3),
+      right:generateLine(new Vec3(5,2,1),new Vec3(0,1,0),3),
+      top:generateLine(new Vec3(3,5,1),new Vec3(1,0,0),2),
+      air:generateLine(new Vec3(3,2,1),new Vec3(0,1,0),3).concat(generateLine(new Vec3(4,2,1),new Vec3(0,1,0),3))
+    })
+  });
+});
+
+describe("Detect portal", function() {
+  var portalData=[];
+  portalData.push({
+    name:"simple portal frame x",
+    bottomLeft:new Vec3(2,1,1),
+    direction:new Vec3(1,0,0),
+    width:4,
+    height:5,
+    additionalAir:[],
+    additionalObsidian:[]
+  });
+  portalData.push({
+    name:"simple portal frame z",
+    bottomLeft:new Vec3(2,1,1),
+    direction:new Vec3(0,0,1),
+    width:4,
+    height:5,
+    additionalAir:[],
+    additionalObsidian:[]
+  });
+  portalData.push({
+    name:"big simple portal frame x",
+    bottomLeft:new Vec3(2,1,1),
+    direction:new Vec3(1,0,0),
+    width:10,
+    height:10,
+    additionalAir:[],
+    additionalObsidian:[]
+  });
+  portalData.push({
+    name:"simple portal frame x with borders",
+    bottomLeft:new Vec3(2,1,1),
+    direction:new Vec3(1,0,0),
+    width:4,
+    height:5,
+    additionalAir:[],
+    additionalObsidian:[new Vec3(2,1,1),new Vec3(5,1,1),new Vec3(2,6,1),new Vec3(5,6,1)]
+  });
+  var {bottom,left,right,top,air}=generatePortal(new Vec3(2,1,2),new Vec3(1,0,0),4,5);
+
+  portalData.push({
+    name:"2 portals",
+    bottomLeft:new Vec3(2,1,1),
+    direction:new Vec3(1,0,0),
+    width:4,
+    height:5,
+    additionalAir:air,
+    additionalObsidian:[].concat.apply([], [bottom, left, right,top])
+  });
+
+
+  portalData.forEach(({name,bottomLeft,direction,width,height,additionalAir,additionalObsidian}) => {
+    var portal=generatePortal(bottomLeft,direction,width,height);
+    var {bottom,left,right,top,air}=portal;
+    describe("Detect "+name,() => {
+      var expectedBorder={bottom,left,right,top};
+
+      var world;
+      before(async function(){
+        world=await makeWorldWithPortal(portal,additionalAir,additionalObsidian);
+      });
+
+
+      describe("detect potential first lines",function(){
+        it("detect potential first lines from bottom left", async function() {
+          let potentialLines=await findPotentialLines(world,bottom[0],new Vec3(0,1,0));
+          assert.include(potentialLines,{
+              "direction": direction,
+              "line": bottom
+            });
+        });
+
+        it("detect potential first lines from bottom right", async function() {
+          let potentialLines=await findPotentialLines(world,bottom[bottom.length-1],new Vec3(0,1,0));
+          assert.include(potentialLines,{
+              "direction": direction,
+              "line": bottom
+            });
+        });
+
+
+        it("detect potential first lines from top left", async function() {
+          let potentialLines=await findPotentialLines(world,top[0],new Vec3(0,-1,0));
+          assert.include(potentialLines,{
+              "direction": direction,
+              "line": top
+            });
+        });
+
+        it("detect potential first lines from top right", async function() {
+          let potentialLines=await findPotentialLines(world,top[top.length-1],new Vec3(0,-1,0));
+          assert.include(potentialLines,{
+              "direction": direction,
+              "line": top
+            });
+        });
+
+        it("detect potential first lines from left top", async function() {
+          let potentialLines=await findPotentialLines(world,left[left.length-1],direction);
+          assert.include(potentialLines,{
+              "direction": new Vec3(0,1,0),
+              "line": left
+            });
+        });
+
+        it("detect potential first lines from right bottom", async function() {
+          let potentialLines=await findPotentialLines(world,right[0],direction.scaled(-1));
+          assert.include(potentialLines,{
+              "direction": new Vec3(0,1,0),
+              "line": right
+            });
+        });
+      });
+
+
+      describe("find borders",function() {
+        it("find borders from bottom", async function () {
+          var border = await findBorder(world, {
+            "direction": direction,
+            "line": bottom
+          }, new Vec3(0, 1, 0));
+          assert.deepEqual(border, expectedBorder)
+        });
+
+        it("find borders from top", async function () {
+          var border = await findBorder(world, {
+            "direction": direction,
+            "line": top
+          }, new Vec3(0, -1, 0));
+          assert.deepEqual(border, expectedBorder)
+        });
+
+        it("find borders from left", async function () {
+          var border = await findBorder(world, {
+            "direction": new Vec3(0, 1, 0),
+            "line": left
+          },direction);
+          assert.deepEqual(border, expectedBorder)
+        });
+        it("find borders from right", async function () {
+          var border = await findBorder(world, {
+            "direction": new Vec3(0, 1, 0),
+            "line": right
+          }, direction.scaled(-1));
+          assert.deepEqual(border, expectedBorder)
+        });
+      });
+
+      describe("detect portals",function(){
+        it("detect portals from bottom left",async function() {
+          var portals=await detectFrame(world,bottom[0],new Vec3(0,1,0));
+          assert.deepEqual(portals,[portal])
+        });
+        it("detect portals from top left",async function() {
+          var portals=await detectFrame(world,top[0],new Vec3(0,-1,0));
+          assert.deepEqual(portals,[portal])
+        });
+        it("detect portals from right top",async function() {
+          var portals=await detectFrame(world,right[right.length-1],direction.scaled(-1));
+          assert.deepEqual(portals,[portal])
+        })
+      });
+
+      it("get air",function(){
+        var foundAir=getAir(expectedBorder);
+        assert.deepEqual(foundAir,air);
+      });
+    });
+  });
+
+
+});
+
+
+describe("Doesn't detect non-portal",function() {
+  var portalData=[];
+
+  portalData.push({
+    name:"simple portal frame x with one obsidian in the middle",
+    bottomLeft:new Vec3(2,1,1),
+    direction:new Vec3(1,0,0),
+    width:5,
+    height:5,
+    additionalAir:[],
+    additionalObsidian:[new Vec3(4,3,1)]
+  });
+
+  portalData.forEach(({name,bottomLeft,direction,width,height,additionalAir,additionalObsidian}) => {
+    var portal = generatePortal(bottomLeft, direction, width, height);
+    var {bottom,left,right,top,air}=portal;
+    describe("Doesn't detect detect " + name, () => {
+      var world;
+      before(async function () {
+        world=await makeWorldWithPortal(portal, additionalAir, additionalObsidian);
+      });
+
+      describe("doesn't detect portals",function(){
+        it("doesn't detect portals from bottom left",async function() {
+          var portals=await detectFrame(world,bottom[0],new Vec3(0,1,0));
+          assert.deepEqual(portals,[])
+        });
+        it("doesn't detect portals from top left",async function() {
+          var portals=await detectFrame(world,top[0],new Vec3(0,-1,0));
+          assert.deepEqual(portals,[])
+        });
+        it("doesn't detect portals from right top",async function() {
+          var portals=await detectFrame(world,right[right.length-1],direction.scaled(-1));
+          assert.deepEqual(portals,[])
+        })
+      });
+
+    });
+  });
+});