diff --git a/assets/src/bundles/browse/origin-search.js b/assets/src/bundles/browse/origin-search.js
--- a/assets/src/bundles/browse/origin-search.js
+++ b/assets/src/bundles/browse/origin-search.js
@@ -200,27 +200,32 @@
   $(document).ready(() => {
     $('#swh-search-origins').submit(event => {
       event.preventDefault();
-      let searchQueryText = $('#swh-origins-url-patterns').val().trim();
-      let withVisit = $('#swh-search-origins-with-visit').prop('checked');
-      let withContent = $('#swh-filter-empty-visits').prop('checked');
-      let searchMetadata = $('#swh-search-origin-metadata').prop('checked');
-      const visitType = $('#swh-search-visit-type').val();
-      let queryParameters = new URLSearchParams();
-      queryParameters.append('q', searchQueryText);
-      if (withVisit) {
-        queryParameters.append('with_visit', withVisit);
-      }
-      if (withContent) {
-        queryParameters.append('with_content', withContent);
-      }
-      if (searchMetadata) {
-        queryParameters.append('search_metadata', searchMetadata);
-      }
-      if (visitType !== 'any') {
-        queryParameters.append('visit_type', visitType);
+      if (event.target.checkValidity()) {
+        $(event.target).removeClass('was-validated');
+        let searchQueryText = $('#swh-origins-url-patterns').val().trim();
+        let withVisit = $('#swh-search-origins-with-visit').prop('checked');
+        let withContent = $('#swh-filter-empty-visits').prop('checked');
+        let searchMetadata = $('#swh-search-origin-metadata').prop('checked');
+        const visitType = $('#swh-search-visit-type').val();
+        let queryParameters = new URLSearchParams();
+        queryParameters.append('q', searchQueryText);
+        if (withVisit) {
+          queryParameters.append('with_visit', withVisit);
+        }
+        if (withContent) {
+          queryParameters.append('with_content', withContent);
+        }
+        if (searchMetadata) {
+          queryParameters.append('search_metadata', searchMetadata);
+        }
+        if (visitType !== 'any') {
+          queryParameters.append('visit_type', visitType);
+        }
+        // Update the url, triggering page reload and effective search
+        window.location = `${Urls.browse_search()}?${queryParameters.toString()}`;
+      } else {
+        $(event.target).addClass('was-validated');
       }
-      // Update the url, triggering page reload and effective search
-      window.location = `${Urls.browse_search()}?${queryParameters.toString()}`;
     });
 
     $('#origins-next-results-button').click(event => {
diff --git a/assets/src/bundles/webapp/webapp-utils.js b/assets/src/bundles/webapp/webapp-utils.js
--- a/assets/src/bundles/webapp/webapp-utils.js
+++ b/assets/src/bundles/webapp/webapp-utils.js
@@ -1,5 +1,5 @@
 /**
- * Copyright (C) 2018-2020  The Software Heritage developers
+ * Copyright (C) 2018-2021  The Software Heritage developers
  * See the AUTHORS file at the top-level directory of this distribution
  * License: GNU Affero General Public License version 3, or any later version
  * See top-level LICENSE file for more information
@@ -168,14 +168,18 @@
   // navbar search form submission callback
   $('#swh-origins-search-top').submit(event => {
     event.preventDefault();
-    let searchQueryText = $('#swh-origins-search-top-input').val().trim();
-    let queryParameters = new URLSearchParams();
-    queryParameters.append('q', searchQueryText);
-    queryParameters.append('with_visit', true);
-    queryParameters.append('with_content', true);
-    window.location = `${Urls.browse_search()}?${queryParameters.toString()}`;
+    if (event.target.checkValidity()) {
+      $(event.target).removeClass('was-validated');
+      let searchQueryText = $('#swh-origins-search-top-input').val().trim();
+      let queryParameters = new URLSearchParams();
+      queryParameters.append('q', searchQueryText);
+      queryParameters.append('with_visit', true);
+      queryParameters.append('with_content', true);
+      window.location = `${Urls.browse_search()}?${queryParameters.toString()}`;
+    } else {
+      $(event.target).addClass('was-validated');
+    }
   });
-
 });
 
 export function initPage(page) {
@@ -355,3 +359,18 @@
     setFullWidth(previousFullWidthState);
   }
 }
+
+export async function validateSWHIDInput(swhidInputElt) {
+  const swhidInput = swhidInputElt.value.trim();
+  let customValidity = '';
+  if (swhidInput.startsWith('swh:')) {
+    const resolveSWHIDUrl = Urls.api_1_resolve_swhid(swhidInput);
+    const response = await fetch(resolveSWHIDUrl);
+    const responseData = await response.json();
+    if (responseData.hasOwnProperty('exception')) {
+      customValidity = responseData.reason;
+    }
+  }
+  swhidInputElt.setCustomValidity(customValidity);
+  $(swhidInputElt).siblings('.invalid-feedback').text(customValidity);
+}
diff --git a/assets/src/bundles/webapp/webapp.css b/assets/src/bundles/webapp/webapp.css
--- a/assets/src/bundles/webapp/webapp.css
+++ b/assets/src/bundles/webapp/webapp.css
@@ -1,5 +1,5 @@
 /**
- * Copyright (C) 2018-2020  The Software Heritage developers
+ * Copyright (C) 2018-2021  The Software Heritage developers
  * See the AUTHORS file at the top-level directory of this distribution
  * License: GNU Affero General Public License version 3, or any later version
  * See top-level LICENSE file for more information
@@ -699,3 +699,7 @@
         right: -65px;
     }
 }
+
+.invalid-feedback {
+    font-size: 100%;
+}
diff --git a/cypress/integration/origin-search.spec.js b/cypress/integration/origin-search.spec.js
--- a/cypress/integration/origin-search.spec.js
+++ b/cypress/integration/origin-search.spec.js
@@ -10,11 +10,21 @@
 let origin;
 let url;
 
-function doSearch(searchText) {
-  cy.get('#swh-origins-url-patterns')
-    .type(searchText)
+function doSearch(searchText, searchInputElt = '#swh-origins-url-patterns') {
+  if (searchText.startsWith('swh:')) {
+    cy.intercept('**/api/1/resolve/**')
+      .as('swhidResolve');
+  }
+  cy.get(searchInputElt)
+    // to avoid sending too much SWHID validation requests
+    // as cypress insert character one by one when using type
+    .invoke('val', searchText.slice(0, -1))
+    .type(searchText.slice(-1))
     .get('.swh-search-icon')
     .click();
+  if (searchText.startsWith('swh:')) {
+    cy.wait('@swhidResolve');
+  }
 }
 
 function searchShouldRedirect(searchText, redirectUrl) {
@@ -25,9 +35,11 @@
 
 function searchShouldShowNotFound(searchText, msg) {
   doSearch(searchText);
-  cy.get('#swh-no-result')
-    .should('be.visible')
-    .and('contain', msg);
+  if (searchText.startsWith('swh:')) {
+    cy.get('.invalid-feedback')
+      .should('be.visible')
+      .and('contain', msg);
+  }
 }
 
 function stubOriginVisitLatestRequests(status = 200, response = {type: 'tar'}, aliasSuffix = '') {
@@ -498,6 +510,28 @@
 
       searchShouldShowNotFound(swhid, msg);
     });
+
+    function checkInvalidSWHIDReport(url, searchInputElt, repoData) {
+      const invalidSWHID = `swh:1:cnt:${repoData.content[0].sha1git};lines=45-60/`;
+      cy.visit(url);
+      doSearch(invalidSWHID, searchInputElt);
+      cy.get(searchInputElt)
+        .then($el => $el[0].checkValidity()).should('be.false');
+      cy.get(searchInputElt)
+        .invoke('prop', 'validationMessage')
+        .should('not.equal', '');
+
+    }
+
+    it('should report invalid SWHID in search page input', function() {
+      checkInvalidSWHIDReport(this.Urls.browse_search(), '#swh-origins-url-patterns', this.unarchivedRepo);
+      cy.get('.invalid-feedback')
+        .should('be.visible');
+    });
+
+    it('should report invalid SWHID in top right search input', function() {
+      checkInvalidSWHIDReport(this.Urls.browse_help(), '#swh-origins-search-top-input', this.unarchivedRepo);
+    });
   });
 
 });
diff --git a/swh/web/templates/includes/origin-search-form.html b/swh/web/templates/includes/origin-search-form.html
--- a/swh/web/templates/includes/origin-search-form.html
+++ b/swh/web/templates/includes/origin-search-form.html
@@ -1,18 +1,20 @@
 {% comment %}
-Copyright (C) 2020  The Software Heritage developers
+Copyright (C) 2020-2021  The Software Heritage developers
 See the AUTHORS file at the top-level directory of this distribution
 License: GNU Affero General Public License version 3, or any later version
 See top-level LICENSE file for more information
 {% endcomment %}
 
-<form class="form-horizontal" id="swh-search-origins">
+<form class="form-horizontal needs-validation" id="swh-search-origins" novalidate>
   <div class="input-group">
     <input class="form-control"
            placeholder="Enter a SWHID to resolve or string pattern(s) to search for in origin urls"
-           type="text" id="swh-origins-url-patterns" autofocus>
+           type="text" id="swh-origins-url-patterns"
+           oninput="swh.webapp.validateSWHIDInput(this)" autofocus required>
     <div class="input-group-append">
       <button class="btn btn-primary" type="submit"><i class="swh-search-icon mdi mdi-24px mdi-magnify" aria-hidden="true"></i></button>
     </div>
+    <div class="invalid-feedback"></div>
   </div>
   <div class="row mt-1 mb-1 float-right position-relative" style="z-index: 1000">
     <div class="form-group form-inline">
diff --git a/swh/web/templates/layout.html b/swh/web/templates/layout.html
--- a/swh/web/templates/layout.html
+++ b/swh/web/templates/layout.html
@@ -1,5 +1,5 @@
 {% comment %}
-Copyright (C) 2015-2020  The Software Heritage developers
+Copyright (C) 2015-2021  The Software Heritage developers
 See the AUTHORS file at the top-level directory of this distribution
 License: GNU Affero General Public License version 3, or any later version
 See top-level LICENSE file for more information
@@ -26,7 +26,7 @@
 /*
 @licstart  The following is the entire license notice for the JavaScript code in this page.
 
-Copyright (C) 2015-2020  The Software Heritage developers
+Copyright (C) 2015-2021  The Software Heritage developers
 
 This program is free software: you can redistribute it and/or modify
 it under the terms of the GNU Affero General Public License as
@@ -149,11 +149,12 @@
           <div class="swh-navbar-content">
             {% block navbar-content %}{% endblock %}
             {% if request.resolver_match.url_name != 'swh-web-homepage' and request.resolver_match.url_name != 'browse-search' %}
-              <form class="form-horizontal d-none d-md-flex input-group swh-search-navbar"
+              <form class="form-horizontal d-none d-md-flex input-group swh-search-navbar needs-validation"
                   id="swh-origins-search-top">
                 <input class="form-control"
                   placeholder="Enter a SWHID to resolve or keyword(s) to search for in origin URLs"
-                  type="text" id="swh-origins-search-top-input"/>
+                  type="text" id="swh-origins-search-top-input"
+                  oninput="swh.webapp.validateSWHIDInput(this)" required/>
                 <div class="input-group-append">
                   <button class="btn btn-primary" type="submit">
                   <i class="swh-search-icon mdi mdi-24px mdi-magnify" aria-hidden="true"></i>