Optimizely Developer
Optimizely Web Experimentation is the platform where the difference between a competent and an incompetent implementation shows up fastest, because its Pages and activation model, and its JavaScript API, are doing real work on your behalf. We build variation code, configure activation and metrics, and debug experiments in Optimizely for agencies and in-house programmes.
CRO strategy, design and development across Shopify, WordPress, Convert, Optimizely, VWO and Adobe Target.
Does this sound familiar?
These are the situations teams actually describe when they get in touch about this, not a generic list of pain points.
Everything is on one Page with immediate activation
Optimizely’s Page concept defines where and when an experiment can run. Teams that put every experiment on a single sitewide Page with immediate activation get experiments trying to execute before their target elements exist, and then blame the platform for the empty variation.
The snippet has been modified or moved
Optimizely’s documentation is explicit that the snippet should be pasted exactly as provided and not modified. Once it has been wrapped in a tag manager, deferred, or edited to “optimise” it, execution order changes and flicker and race conditions follow.
setTimeout is standing in for waitForElement
Optimizely exposes utility methods through window.optimizely.get('utils'). utils.waitForElement(selector) resolves when a matching element exists, and utils.waitUntil(condition) polls a condition. Code that instead guesses at a delay works on the developer’s connection and fails on a slow one.
The SPA re-render is fighting the variation
Optimizely uses a MutationObserver to detect DOM changes and reapply changes at the right moment. Custom code that does not cooperate with that, or that reapplies without checking whether it already has, produces duplicated elements and listeners bound several times over.
Metrics and events do not mean what the report implies
An event bound to a selector that matches more than intended, or a primary metric that is not the hypothesis. The experiment concludes, and the conclusion is about something else.
What is included
Scope stated as specific outputs rather than as adjectives.
- Variation code in custom JavaScript and CSS, written against your real DOM
- Page definitions and the right activation mode per experiment: immediate, manual, callback or polling
- Use of the Optimizely JavaScript API where it is the correct tool:
window.optimizely.get('state'),get('visitor'),get('data'), and theutilshelpers - SPA and dynamic-content handling built on
utils.waitForElementandutils.waitUntilrather than fixed delays - Audience configuration, including custom attributes and cookie or dataLayer-driven segments
- Event and metric implementation, with the primary metric matched to the stated hypothesis
- Project-level JavaScript for shared instrumentation, kept separate from experiment logic
- Redirect experiment implementation, with parameter and referrer preservation handled properly
- Exclusion group setup where concurrent experiments would otherwise overlap
- Debugging of activation, bucketing and measurement failures
- Full pre-launch QA and post-launch validation, including a traffic-split check
How the work runs
- 1
Read the existing project before adding to it
Pages, audiences, events, project JavaScript and exclusion groups. In a mature Optimizely project most implementation mistakes come from ignoring conventions that are already there.
- 2
Choose the activation model deliberately
Whether the experiment should activate immediately, on a condition, or via a callback is a decision with consequences for flicker and correctness. We make it explicitly and write down why.
- 3
Build the variation against the platform’s own hooks
Element readiness handled with the documented utilities, reapplication made idempotent, listeners cleaned up so a re-render does not bind them twice.
- 4
Instrument, QA, launch
Metrics verified on every arm, full pre-launch matrix, then a live-traffic check that the experiment is decisioning and recording as configured.
Who this is for
Enterprise in-house experimentation teams
Optimizely is most often the enterprise choice, which means governance, exclusion groups and multiple concurrent programmes, plus a queue of builds waiting on internal engineering.
Agencies delivering into a client’s Optimizely account
You need someone who can work inside an established Page and audience structure without disrupting it.
Teams with client-rendered front ends
React and other SPA stacks are where Optimizely implementations most often go wrong, and where knowing the platform’s own re-application model matters most.
Optimizely surface we work in
Named specifically, because “modern tooling” tells a buyer nothing.
- Optimizely Web Experimentation
- Custom JavaScript and CSS per variation
- Pages and activation modes (immediate, manual, callback, polling)
- JavaScript API:
window.optimizely.get(...) utils.waitForElementandutils.waitUntil- Audiences and custom visitor attributes
- Events and metrics
- Project JavaScript
- Redirect experiments
- Exclusion groups
- Experimentation REST API for programmatic setup and reporting
How this gets checked
Every engagement carries a QA pass. It is written down so that “QA done” means something specific.
- Activation verified: does the experiment decide at the intended moment, once, per session
- Variation verified after client-side route change and component re-render
- No duplicated elements or double-bound listeners after repeated reapplication
- Audience conditions checked from qualifying and non-qualifying sessions
- Every metric triggered manually and confirmed recorded on control and variation
- Flicker measured with the snippet in its production position
- Traffic split and bucketing checked once live
Ways to work together
The commercial shape is chosen after we know the scope, not before.
Dedicated partnership
Reserved capacity for a steady pipeline of work.
Flexible hours
Draw down specialist time as the work arrives.
Project engagement
A defined scope, owned end to end.
All three are described in full under engagement models.
Questions people ask before buying this
Optimizely Web Experimentation documentation
Platform behaviour described on this page was checked against the vendor’s own current documentation. Verify against these before relying on any of it, because vendors change APIs.
Services on this platform
Other experimentation platforms
Further reading
Hire an Optimizely Developer
Send us the experiment you need built, or the project you have inherited. We will tell you what we would do and what we would fix first.