diff --git a/backend/LexBoxApi/GraphQL/CustomTypes/IsLanguageForgeProjectDataLoader.cs b/backend/LexBoxApi/GraphQL/CustomTypes/IsLanguageForgeProjectDataLoader.cs
new file mode 100644
index 000000000..74037310b
--- /dev/null
+++ b/backend/LexBoxApi/GraphQL/CustomTypes/IsLanguageForgeProjectDataLoader.cs
@@ -0,0 +1,30 @@
+using LexCore.ServiceInterfaces;
+using LfClassicData;
+using MongoDB.Driver;
+using MongoDB.Driver.Linq;
+
+namespace LexBoxApi.GraphQL.CustomTypes;
+
+public class IsLanguageForgeProjectDataLoader : BatchDataLoader<string, bool>, IIsLanguageForgeProjectDataLoader
+{
+    private readonly SystemDbContext _systemDbContext;
+
+    public IsLanguageForgeProjectDataLoader(
+        SystemDbContext systemDbContext,
+        IBatchScheduler batchScheduler,
+        DataLoaderOptions? options = null)
+        : base(batchScheduler, options)
+    {
+        _systemDbContext = systemDbContext;
+    }
+
+    protected override async Task<IReadOnlyDictionary<string, bool>> LoadBatchAsync(
+        IReadOnlyList<string> projectCodes,
+        CancellationToken cancellationToken)
+    {
+        return await MongoExtensions.ToAsyncEnumerable(_systemDbContext.Projects.AsQueryable()
+            .Select(p => p.ProjectCode)
+            .Where(projectCode => projectCodes.Contains(projectCode)))
+            .ToDictionaryAsync(projectCode => projectCode, _ => true, cancellationToken);
+    }
+}
diff --git a/backend/LexBoxApi/GraphQL/GraphQlSetupKernel.cs b/backend/LexBoxApi/GraphQL/GraphQlSetupKernel.cs
index fd0457973..252da0584 100644
--- a/backend/LexBoxApi/GraphQL/GraphQlSetupKernel.cs
+++ b/backend/LexBoxApi/GraphQL/GraphQlSetupKernel.cs
@@ -20,6 +20,7 @@ public static void AddLexGraphQL(this IServiceCollection services, IHostEnvironm
             .InitializeOnStartup()
             .RegisterDbContext<LexBoxDbContext>()
             .RegisterService<IHgService>()
+            .RegisterService<IIsLanguageForgeProjectDataLoader>()
             .RegisterService<LoggedInContext>()
             .RegisterService<EmailService>()
             .RegisterService<LexAuthService>()
diff --git a/backend/LexBoxApi/LexBoxKernel.cs b/backend/LexBoxApi/LexBoxKernel.cs
index 899f21444..4281d81b6 100644
--- a/backend/LexBoxApi/LexBoxKernel.cs
+++ b/backend/LexBoxApi/LexBoxKernel.cs
@@ -1,6 +1,7 @@
 using LexBoxApi.Auth;
 using LexBoxApi.Config;
 using LexBoxApi.GraphQL;
+using LexBoxApi.GraphQL.CustomTypes;
 using LexBoxApi.Services;
 using LexCore.Config;
 using LexCore.ServiceInterfaces;
@@ -52,6 +53,7 @@ public static void AddLexBoxApi(this IServiceCollection services,
         services.AddScoped<TusService>();
         services.AddScoped<TurnstileService>();
         services.AddScoped<IHgService, HgService>();
+        services.AddScoped<IIsLanguageForgeProjectDataLoader, IsLanguageForgeProjectDataLoader>();
         services.AddScoped<ILexProxyService, LexProxyService>();
         services.AddSingleton<ISendReceiveService, SendReceiveService>();
         services.AddSingleton<LexboxLinkGenerator>();
diff --git a/backend/LexCore/Entities/Project.cs b/backend/LexCore/Entities/Project.cs
index 5758c0d29..37f2e9b32 100644
--- a/backend/LexCore/Entities/Project.cs
+++ b/backend/LexCore/Entities/Project.cs
@@ -50,6 +50,15 @@ public bool GetHasAbandonedTransactions(IHgService hgService)
     {
         return hgService.HasAbandonedTransactions(Code);
     }
+
+    public Task<bool> GetIsLanguageForgeProject(IIsLanguageForgeProjectDataLoader loader)
+    {
+        if (Type is ProjectType.Unknown or ProjectType.FLEx)
+        {
+            return loader.LoadAsync(Code);
+        }
+        return Task.FromResult(false);
+    }
 }
 
 public enum ProjectMigrationStatus
diff --git a/backend/LexCore/ServiceInterfaces/IIsLanguageForgeProjectDataLoader.cs b/backend/LexCore/ServiceInterfaces/IIsLanguageForgeProjectDataLoader.cs
new file mode 100644
index 000000000..6482581b2
--- /dev/null
+++ b/backend/LexCore/ServiceInterfaces/IIsLanguageForgeProjectDataLoader.cs
@@ -0,0 +1,6 @@
+namespace LexCore.ServiceInterfaces;
+
+public interface IIsLanguageForgeProjectDataLoader
+{
+    public Task<bool> LoadAsync(string projectCode, CancellationToken cancellationToken = default);
+}
diff --git a/frontend/schema.graphql b/frontend/schema.graphql
index 93b8a9056..dddbfd48d 100644
--- a/frontend/schema.graphql
+++ b/frontend/schema.graphql
@@ -214,6 +214,7 @@ type Project {
   users: [ProjectUsers!]!
   changesets: [Changeset!]!
   hasAbandonedTransactions: Boolean!
+  isLanguageForgeProject: Boolean!
   parentId: UUID
   name: String!
   description: String
diff --git a/frontend/src/routes/(authenticated)/project/[project_code]/+page.svelte b/frontend/src/routes/(authenticated)/project/[project_code]/+page.svelte
index d470585ce..6e9b6df43 100644
--- a/frontend/src/routes/(authenticated)/project/[project_code]/+page.svelte
+++ b/frontend/src/routes/(authenticated)/project/[project_code]/+page.svelte
@@ -234,12 +234,14 @@
   <HeaderPage wide title={project.name}>
     <svelte:fragment slot="actions">
       {#if project.type === ProjectType.FlEx && $isDev}
+        {#if project.isLanguageForgeProject}
           <a href="./{project.code}/viewer" class="btn btn-neutral text-[#DCA54C] flex items-center gap-2">
             {$t('project_page.open_with_viewer')}
             <span class="i-mdi-dictionary text-2xl" />
           </a>
-          <OpenInFlexModal bind:this={openInFlexModal} {project}/>
-          <OpenInFlexButton projectId={project.id} on:click={openInFlexModal.open}/>
+        {/if}
+        <OpenInFlexModal bind:this={openInFlexModal} {project}/>
+        <OpenInFlexButton projectId={project.id} on:click={openInFlexModal.open}/>
       {:else}
         <Dropdown>
           <button class="btn btn-primary">
diff --git a/frontend/src/routes/(authenticated)/project/[project_code]/+page.ts b/frontend/src/routes/(authenticated)/project/[project_code]/+page.ts
index a523be2e7..9141f6979 100644
--- a/frontend/src/routes/(authenticated)/project/[project_code]/+page.ts
+++ b/frontend/src/routes/(authenticated)/project/[project_code]/+page.ts
@@ -45,6 +45,7 @@ export async function load(event: PageLoadEvent) {
 						createdDate
 						retentionPolicy
 						isConfidential
+            isLanguageForgeProject
 						users {
 							id
 							role