diff --git a/frontends/dnet-is-application/src/app/dsm/dsm-add-api.dialog.html b/frontends/dnet-is-application/src/app/dsm/dsm-add-api.dialog.html
index 309197d9..bc7fb221 100644
--- a/frontends/dnet-is-application/src/app/dsm/dsm-add-api.dialog.html
+++ b/frontends/dnet-is-application/src/app/dsm/dsm-add-api.dialog.html
@@ -60,8 +60,10 @@
                 <mat-form-field appearance="fill" floatLabel="always" style="width: 100%;">
                     <mat-label>Base URL</mat-label>
                     <input matInput formControlName="baseurl" />
-                    <mat-error *ngIf="addApiForm.get('baseurl')?.invalid">This field is
-                        <strong>required</strong></mat-error>
+                    <mat-error *ngIf="addApiForm.get('baseurl')?.invalid">
+                        Invalid URL
+                        <span *ngIf="addApiForm.get('baseurl')?.hasError('required')">: This field is <strong>required</strong></span>
+                    </mat-error>
                 </mat-form-field>
 
                 <ng-container *ngFor="let p of selProtParams">
diff --git a/frontends/dnet-is-application/src/app/dsm/dsm.component.ts b/frontends/dnet-is-application/src/app/dsm/dsm.component.ts
index 32ac9477..563948b3 100644
--- a/frontends/dnet-is-application/src/app/dsm/dsm.component.ts
+++ b/frontends/dnet-is-application/src/app/dsm/dsm.component.ts
@@ -179,7 +179,7 @@ export class DsmAddApiDialog {
     compatibility : new FormControl('', [Validators.required]),
     contentdescription : new FormControl('', [Validators.required]),
     protocol : new FormControl('', [Validators.required]),
-    baseurl : new FormControl('', [Validators.required]),
+    baseurl : new FormControl('', [Validators.required, Validators.pattern('^(http|https|ftp|file|sftp|jar|mongodb):\/\/')]),
     metadataIdentifierPath : new FormControl('', [Validators.required])
   });