diff --git a/src/debugging.js b/src/debugging.js
new file mode 100644
index 000000000000..39ddc92beeed
--- /dev/null
+++ b/src/debugging.js
@@ -0,0 +1,89 @@
+
+import { config } from 'src/config';
+import { logMessage as utilsLogMessage, logWarn as utilsLogWarn } from 'src/utils';
+import { addBidResponse } from 'src/auction';
+
+const OVERRIDE_KEY = '$$PREBID_GLOBAL$$:debugging';
+
+export let boundHook;
+
+function logMessage(msg) {
+  utilsLogMessage('DEBUG: ' + msg);
+}
+
+function logWarn(msg) {
+  utilsLogWarn('DEBUG: ' + msg);
+}
+
+function enableOverrides(overrides, fromSession = false) {
+  config.setConfig({'debug': true});
+  logMessage(`bidder overrides enabled${fromSession ? ' from session' : ''}`);
+
+  if (boundHook) {
+    addBidResponse.removeHook(boundHook);
+  }
+
+  boundHook = addBidResponseHook.bind(null, overrides);
+  addBidResponse.addHook(boundHook, 5);
+}
+
+export function disableOverrides() {
+  if (boundHook) {
+    addBidResponse.removeHook(boundHook);
+    logMessage('bidder overrides disabled');
+  }
+}
+
+export function addBidResponseHook(overrides, adUnitCode, bid, next) {
+  if (Array.isArray(overrides.bidders) && overrides.bidders.indexOf(bid.bidderCode) === -1) {
+    logWarn(`bidder '${bid.bidderCode}' excluded from auction by bidder overrides`);
+    return;
+  }
+
+  if (Array.isArray(overrides.bids)) {
+    overrides.bids.forEach(overrideBid => {
+      if (overrideBid.bidder && overrideBid.bidder !== bid.bidderCode) {
+        return;
+      }
+      if (overrideBid.adUnitCode && overrideBid.adUnitCode !== adUnitCode) {
+        return;
+      }
+
+      bid = Object.assign({}, bid);
+
+      Object.keys(overrideBid).filter(key => ['bidder', 'adUnitCode'].indexOf(key) === -1).forEach((key) => {
+        let value = overrideBid[key];
+        logMessage(`bidder overrides changed '${adUnitCode}/${bid.bidderCode}' bid.${key} from '${bid[key]}' to '${value}'`);
+        bid[key] = value;
+      });
+    });
+  }
+
+  next(adUnitCode, bid);
+}
+
+export function getConfig(debugging) {
+  if (!debugging.enabled) {
+    disableOverrides();
+    try {
+      window.sessionStorage.removeItem(OVERRIDE_KEY);
+    } catch (e) {}
+  } else {
+    try {
+      window.sessionStorage.setItem(OVERRIDE_KEY, JSON.stringify(debugging));
+    } catch (e) {}
+    enableOverrides(debugging);
+  }
+}
+config.getConfig('debugging', ({debugging}) => getConfig(debugging));
+
+export function sessionLoader() {
+  let overrides;
+  try {
+    overrides = JSON.parse(window.sessionStorage.getItem(OVERRIDE_KEY));
+  } catch (e) {
+  }
+  if (overrides) {
+    enableOverrides(overrides, true);
+  }
+}
diff --git a/src/hook.js b/src/hook.js
index 6c6cefdc56c7..fef62a37c3d7 100644
--- a/src/hook.js
+++ b/src/hook.js
@@ -60,6 +60,9 @@ export function createHook(type, fn, hookName) {
     },
     removeHook: function(removeFn) {
       _hooks = _hooks.filter(hook => hook.fn === fn || hook.fn !== removeFn);
+    },
+    hasHook: function(fn) {
+      return _hooks.some(hook => hook.fn === fn);
     }
   };
 
diff --git a/src/prebid.js b/src/prebid.js
index d703df43bf57..d4fbe17a5014 100644
--- a/src/prebid.js
+++ b/src/prebid.js
@@ -9,6 +9,7 @@ import { config } from './config';
 import { auctionManager } from './auctionManager';
 import { targeting, getOldestBid, RENDERED, BID_TARGETING_SET } from './targeting';
 import { createHook } from 'src/hook';
+import { sessionLoader } from 'src/debugging';
 import includes from 'core-js/library/fn/array/includes';
 
 const $$PREBID_GLOBAL$$ = getGlobal();
@@ -27,6 +28,9 @@ const eventValidators = {
   bidWon: checkDefinedPlacement
 };
 
+// initialize existing debugging sessions if present
+sessionLoader();
+
 /* Public vars */
 $$PREBID_GLOBAL$$.bidderSettings = $$PREBID_GLOBAL$$.bidderSettings || {};
 
diff --git a/test/spec/debugging_spec.js b/test/spec/debugging_spec.js
new file mode 100644
index 000000000000..39b08075e060
--- /dev/null
+++ b/test/spec/debugging_spec.js
@@ -0,0 +1,141 @@
+
+import { expect } from 'chai';
+import { sessionLoader, addBidResponseHook, getConfig, disableOverrides, boundHook } from 'src/debugging';
+import { addBidResponse } from 'src/auction';
+import { config } from 'src/config';
+
+describe('bid overrides', () => {
+  let sandbox;
+
+  beforeEach(() => {
+    sandbox = sinon.sandbox.create();
+  });
+
+  afterEach(() => {
+    sandbox.restore();
+  });
+
+  describe('initialization', () => {
+    beforeEach(() => {
+      sandbox.stub(config, 'setConfig');
+      sandbox.stub(window.sessionStorage, 'setItem');
+      sandbox.stub(window.sessionStorage, 'removeItem');
+    });
+
+    afterEach(() => {
+      disableOverrides();
+    });
+
+    it('should happen when enabled with setConfig', () => {
+      getConfig({
+        enabled: true
+      });
+
+      expect(addBidResponse.hasHook(boundHook)).to.equal(true);
+    });
+
+    it('should happen when configuration found in sessionStorage', () => {
+      sandbox.stub(window.sessionStorage, 'getItem').returns('{"enabled": true}');
+
+      sessionLoader();
+      expect(addBidResponse.hasHook(boundHook)).to.equal(true);
+    });
+
+    it('should not throw if sessionStorage is inaccessible', () => {
+      sandbox.stub(window.sessionStorage, 'getItem').throws();
+
+      expect(() => {
+        sessionLoader();
+      }).not.to.throw();
+    });
+  });
+
+  describe('hook', () => {
+    let mockBids;
+    let bids;
+
+    beforeEach(() => {
+      let baseBid = {
+        'bidderCode': 'rubicon',
+        'width': 970,
+        'height': 250,
+        'statusMessage': 'Bid available',
+        'mediaType': 'banner',
+        'source': 'client',
+        'currency': 'USD',
+        'cpm': 0.5,
+        'ttl': 300,
+        'netRevenue': false,
+        'adUnitCode': '/19968336/header-bid-tag-0'
+      };
+      mockBids = [];
+      mockBids.push(baseBid);
+      mockBids.push(Object.assign({}, baseBid, {
+        bidderCode: 'appnexus'
+      }));
+
+      bids = [];
+    });
+
+    function run(overrides) {
+      mockBids.forEach(bid => {
+        addBidResponseHook(overrides, bid.adUnitCode, bid, (adUnitCode, bid) => {
+          bids.push(bid);
+        })
+      });
+    }
+
+    it('should allow us to exclude bidders', () => {
+      run({
+        enabled: true,
+        bidders: ['appnexus']
+      });
+
+      expect(bids.length).to.equal(1);
+      expect(bids[0].bidderCode).to.equal('appnexus');
+    });
+
+    it('should allow us to override all bids', () => {
+      run({
+        enabled: true,
+        bids: [{
+          cpm: 2
+        }]
+      });
+
+      expect(bids.length).to.equal(2);
+      expect(bids[0].cpm).to.equal(2);
+      expect(bids[1].cpm).to.equal(2);
+    });
+
+    it('should allow us to override bids by bidder', () => {
+      run({
+        enabled: true,
+        bids: [{
+          bidder: 'rubicon',
+          cpm: 2
+        }]
+      });
+
+      expect(bids.length).to.equal(2);
+      expect(bids[0].cpm).to.equal(2);
+      expect(bids[1].cpm).to.equal(0.5);
+    });
+
+    it('should allow us to override bids by adUnitCode', () => {
+      mockBids[1].adUnitCode = 'test';
+
+      run({
+        enabled: true,
+        bids: [{
+          adUnitCode: 'test',
+          cpm: 2
+        }]
+      });
+
+      expect(bids.length).to.equal(2);
+      expect(bids[0].cpm).to.equal(0.5);
+      expect(bids[1].cpm).to.equal(2);
+    });
+  });
+});