Modernize a Classic SharePoint Site Safely: Practical Checklist for SharePoint Owners

Classic SharePoint sites still run in many organizations, but they lack modern features like mobile responsiveness, Power Apps integration, and Microsoft Teams connectivity. Microsoft has not removed classic site functionality, but new site templates and most future innovations target modern sites. This article provides a practical checklist for site owners who want to modernize a classic SharePoint site without breaking existing content, permissions, or workflows.

What Makes a SharePoint Site Classic vs Modern

A classic SharePoint site uses the older user interface from SharePoint 2010 or 2013. Classic sites rely on on-page Silverlight controls, legacy web parts, and a fixed-width layout. Modern sites use responsive design, Fluent UI controls, and integration with Microsoft Lists, Power Automate, and Teams.

The technical difference is the site template. Classic sites are created from templates like STS#0 (Team Site), BLANKINTERNET#0 (Publishing Site), or BLOG#0 (Blog). Modern sites use GROUP#0 (Team site connected to a Microsoft 365 group) or SITEPAGEPUBLISHING#0 (Communication site).

You can identify a classic site by opening Site settings > Site information. If the site does not show a Microsoft 365 group or a modern home page, it is classic. You can verify the template in SharePoint admin center > Active sites > select the site > look at the Template column.

Modernization does not require rebuilding the site. SharePoint Online supports a hybrid state where the site collection remains classic but individual pages, lists, and libraries use modern rendering. This approach minimizes risk.

Pre-Modernization Checklist

Before making any changes, complete these checks. Missing any step can break workflows, custom scripts, or inherited permissions.

1. Audit all custom scripts and web parts
   Open Site settings > Web parts. Identify any web part that uses SharePoint Designer workflows, InfoPath forms, or JavaScript that references classic HTML IDs. Modern pages use different DOM structure. Script that manipulates classic page elements will fail on modern pages.
2. Check for SharePoint Designer workflows
   SharePoint Designer 2010 and 2013 workflows are deprecated and do not run on modern pages. If your site uses these workflows, migrate them to Power Automate first. Use Site settings > Workflows to list all active workflows.
3. Review custom master pages
   Classic sites often use custom master pages (seattle.master or oslo.master). Modern sites ignore custom master pages. If you have branding applied through the master page, capture the CSS and apply it via the modern theme or SharePoint Framework extension.
4. Document current permissions
   Go to Site permissions > Check permissions. Write down any unique permissions that break inheritance. Modernization does not change permission inheritance, but verifying the baseline helps if something breaks during the transition.
5. Backup the site
   In SharePoint admin center > Active sites > select the site > click Backup. SharePoint Online creates a site collection backup that you can restore within 14 days. This is the only way to revert a full modernization.

Steps to Modernize a Classic SharePoint Site

Follow these steps in order. Each step is reversible except the final page conversion. Test each step on a staging copy of the site before applying it to production.

1. Enable modern lists and libraries
   Go to Site settings > Site collection features. Activate the feature named Modern List and Library Experience. This changes the rendering of all document libraries and lists from classic to modern without affecting the site pages. Users will see the new toolbar, column filtering, and file preview.
2. Convert the home page to a modern page
   On the home page, click the gear icon > Modernize the site page. SharePoint creates a copy of the existing page as a modern wiki page. The original classic page remains as a backup. If the conversion fails, delete the modern page and restore the classic one from Site pages library.
3. Replace classic web parts with modern equivalents
   Edit the modern home page and remove any classic web parts. Add modern web parts such as File Viewer, Quick Links, Highlighted Content, or Microsoft Embed. Classic web parts like Content Editor or Script Editor do not render in modern pages.
4. Connect the site to a Microsoft 365 group
   In Site settings > Site information, click Connect to a new Microsoft 365 group. This creates a group with the same name as the site and enables Teams integration. This step is optional but recommended for full modern collaboration.
5. Convert remaining classic pages
   Use the PnP Modernization tool. Download the PnP Modernization PowerShell module from the PowerShell Gallery. Run Convert-PnPPageToModern for each wiki or web part page. The tool maps classic web parts to modern equivalents where possible and logs any failures.
6. Enable modern search experience
   In Site settings > Search settings, select the modern search experience. Classic search results pages use a different layout. Modern search integrates with Microsoft Search and shows results from across Microsoft 365.

Common Issues After Modernization

Classic web parts show an error on the modern page

Some classic web parts do not have a modern equivalent. The web part displays a red box with the message This web part is not supported on modern pages. Remove the web part from the page and replace it with a modern web part or a SharePoint Framework extension. For example, replace the Content Search web part with the Highlighted Content web part.

Custom branding disappears after modernization

Modern sites use themes rather than master pages. If your classic site used a custom master page, the branding disappears. Apply the branding using SharePoint admin center > Settings > Theme. Upload a custom theme JSON file. If you need more control, use a SharePoint Framework application customizer to inject CSS.

Workflows stop triggering

SharePoint Designer 2010 workflows are deprecated. They will not run on modern lists or libraries. Migrate these workflows to Power Automate. For SharePoint Designer 2013 workflows, they continue to work on modern lists but Microsoft recommends migration. Check the workflow status in Site settings > Workflows and replace them with Power Automate flows.

Subsites remain classic

Modernization applies only to the site collection root. Subsites created from classic templates remain classic. You must repeat the modernization steps for each subsite. Alternatively, create a new modern site and move content using SharePoint Migration Tool.

Item	Classic Site	Modern Site
Home page type	Classic wiki or web part page	Modern wiki page or article page
List and library experience	Classic toolbar, no column filtering	Modern toolbar, column filtering, file preview
Master page support	Custom seattle.master or oslo.master	No master page; uses theme and SPFx extensions
Microsoft 365 group connection	Not available	Built-in group for Teams and Planner
Mobile responsiveness	Fixed width, requires zoom	Responsive layout, touch-friendly

Modernizing a classic SharePoint site takes planning but does not require a full rebuild. Start by enabling modern lists and libraries, then convert the home page, and finally migrate remaining pages with the PnP Modernization tool. Always test on a staging copy first. After modernization, review the site for broken web parts and workflows. The result is a site that works on mobile devices, integrates with Teams, and supports Power Platform tools.