A Sitecore-to-Optimizely migration breaks four things most reliably: media URLs (Sitecore's /-/media/ paths don't exist in Optimizely), the mapping between Sitecore renderings and Optimizely blocks, personalization and multi-language variants that were stored differently in each platform, and any URL that depended on Sitecore's item tree instead of an explicit route. None of these throw errors at build time. They surface as broken images, empty content areas, and 404s that only appear once real traffic and crawlers hit the live site. This guide covers what breaks, why, and the checks that catch each failure before go-live rather than after.
1. Media library URLs and asset references
Sitecore serves media through the /-/media/ or /~/media/ handler, often with query-string dimensions like ?w=800&h=600. Optimizely uses a Content Delivery Media model with entirely different URL structure. Every hardcoded image path in rich-text fields, every inline SVG reference, and every PDF link that pointed at the old handler will 404 unless you rewrite it.
The trap: your CMS-managed hero images usually migrate cleanly because they move through the field-mapping layer. The ones that break are buried inside body copy — editors who pasted an image URL directly into a rich-text editor five years ago. There is no field mapping that catches those.
How to catch it: crawl the source site and extract every asset reference from rendered HTML, not just from the content model. Diff that inventory against the assets that actually made it into Optimizely's media tree. Orphaned references — assets linked in content but never migrated — are the single biggest source of post-launch image breakage.
2. Renderings, sublayouts, and the block model gap
Sitecore composes pages from renderings and sublayouts placed into placeholders. Optimizely composes pages from Blocks placed into Content Areas. The concepts rhyme but do not map one-to-one, and this is where content silently disappears.
- Datasource-driven renderings in Sitecore point at a shared item. If two pages reused the same datasource, a naive migration either duplicates the block or drops the reference entirely.
- Nested placeholders (a rendering inside a rendering) rarely translate into Optimizely's flatter content-area model without manual restructuring.
- Rendering parameters — the per-instance settings that control spacing, color, or variant — usually have no home in the new block schema and are lost.
How to catch it: build a rendering-to-block coverage matrix before you migrate a single page. Every Sitecore rendering type needs an explicit Optimizely target or a documented decision to kill it. Any rendering with no mapping is a content area that will render empty.
3. URLs, item paths, and redirect risk
Sitecore URLs frequently derive from the content-tree structure, and many sites relied on Sitecore's display-name logic, wildcards, or link-provider settings to produce clean paths. Optimizely generates URLs from its own routing and the page hierarchy you rebuild. Even when the visible URL looks identical, the underlying resolution is different, and edge cases diverge.
Common breakage patterns:
| Sitecore behavior | What breaks in Optimizely |
|---|---|
| Wildcard items serving dynamic routes | No equivalent; needs custom routing or partial routers |
| Display name differs from item name | URL segment changes, old link 404s |
| Trailing-slash and casing rules | Duplicate URLs or redirect loops if not normalized |
Language embedded in path (/en/) | Optimizely language routing may place it differently |
How to catch it: generate the full source URL set from live crawl data and server logs, not from the sitemap alone. Sitemaps miss the long tail that still earns traffic and links. Then confirm each URL either survives unchanged or has a 301 target. Our Sitecore-to-Optimizely guide walks through building that map, and the migration overview covers the redirect-testing pass in more detail.
4. Languages, versions, and personalization
Sitecore stores every language as a version of the same item; Optimizely uses a master-language model with language branches. If a page had a German version but no French, or a partially translated version, the migration logic has to decide what happens — and the default is often to create empty shells or fall back to the master language silently.
Personalization rules and A/B test variants defined in Sitecore's rules engine do not carry over at all. Treat them as content to re-author in Optimizely, not data to migrate.
How to catch it: inventory language-version completeness per item before migration. Any item where the version count doesn't match your expected locale set needs a human decision, not an automated one.
5. SEO and AEO signals that quietly degrade
Beyond outright 404s, replatforming erodes the signals that keep you in Google's index and in AI answer engines:
- Canonical tags that pointed at Sitecore URLs and now self-reference the wrong path.
- Structured data (JSON-LD) built by Sitecore renderings that no longer emit after the block swap.
- Meta titles and descriptions stored in Sitecore standard-values templates that don't map to Optimizely SEO fields.
- Internal link equity lost when body-copy links point at dead media or old item paths.
AI answer engines are less forgiving than traditional crawlers here: a page with broken structured data and missing canonicals is far less likely to be cited even if it renders fine to a human.
A pre-go-live checklist
- Crawl the source site fully; reconcile every asset reference against migrated media.
- Produce a rendering-to-block coverage matrix with zero unmapped renderings.
- Validate the full URL set — including log-derived long tail — against redirects.
- Confirm language-version completeness item by item.
- Spot-check canonicals, JSON-LD, and meta fields on a representative sample of top pages.
- Diff rendered HTML of source vs. staging for your top 200 pages, not just spot pages.
The pattern across all five failure modes is the same: the content model migrates, but the rendered output is where breakage hides. Comparing what the old site actually served against what the new one produces — page by page, asset by asset — is the only reliable way to find these before your users and Googlebot do.