diff --git a/server/webserver.py b/server/webserver.py
index e617255..3a9029f 100644
--- a/server/webserver.py
+++ b/server/webserver.py
@@ -1,5 +1,6 @@
 import json
 import logging
+import re
 from datetime import datetime, timedelta
 from threading import Thread
 
@@ -8,7 +9,8 @@ import pytz
 from bottle import run, request, response, template
 
 from core.config import MAX_SPOT_AGE, ALLOW_SPOTTING
-from core.constants import BANDS, ALL_MODES, MODE_TYPES, SIGS, CONTINENTS, SOFTWARE_VERSION
+from core.constants import BANDS, ALL_MODES, MODE_TYPES, SIGS, CONTINENTS, SOFTWARE_VERSION, UNKNOWN_BAND
+from core.lookup_helper import lookup_helper
 from core.prometheus_metrics_handler import page_requests_counter, get_metrics, api_requests_counter
 from data.spot import Spot
 
@@ -138,13 +140,31 @@ class WebServer:
             json_spot = json.loads(post_data)
             spot = Spot(**json_spot)
 
-            # Reject if no timestamp or dx_call
-            if not spot.time or not spot.dx_call:
+            # Reject if no timestamp, frequency, dx_call or de_call
+            if not spot.time or not spot.dx_call or not spot.freq or not spot.de_call:
                 response.content_type = 'application/json'
                 response.status = 422
-                return json.dumps("Error - 'time' and 'dx_call' must be provided as a minimum.",
+                return json.dumps("Error - 'time', 'dx_call', 'freq' and 'de_call' must be provided as a minimum.",
                                   default=serialize_everything)
 
+            # Reject invalid-looking callsigns
+            if not re.match(r"^[A-Za-z0-9/\-]*$", spot.dx_call):
+                response.content_type = 'application/json'
+                response.status = 422
+                return json.dumps("Error - '" + spot.dx_call + "' does not look like a valid callsign.",
+                                  default=serialize_everything)
+            if not re.match(r"^[A-Za-z0-9/\-]*$", spot.de_call):
+                response.content_type = 'application/json'
+                response.status = 422
+                return json.dumps("Error - '" + spot.de_call + "' does not look like a valid callsign.",
+                                  default=serialize_everything)
+
+            # Reject if frequency not in a known band
+            if lookup_helper.infer_band_from_freq(spot.freq) == UNKNOWN_BAND:
+                response.content_type = 'application/json'
+                response.status = 422
+                return json.dumps("Error - Frequency of " + str(spot.freq / 1000.0) + "kHz is not in a known band.", default=serialize_everything)
+
             # infer missing data, and add it to our database.
             spot.source = "API"
             spot.icon = "desktop"
diff --git a/views/webpage_add_spot.tpl b/views/webpage_add_spot.tpl
index a53a768..8793409 100644
--- a/views/webpage_add_spot.tpl
+++ b/views/webpage_add_spot.tpl
@@ -1,7 +1,10 @@
 % rebase('webpage_base.tpl')
 
-<div class="alert alert-warning fade show mb-0 mt-4" role="alert">
-    Please note that spots added to Spothole are not currently sent "upstream" to DX clusters or xOTA spotting sites.
+<div id="add-spot-intro-box" class="permanently-dismissible-box mt-3">
+<div class="alert alert-primary alert-dismissible fade show" role="alert">
+  <i class="fa-solid fa-circle-info"></i> <strong>Adding spots to Spothole</strong><br/>This page is implemented as a proof of concept for adding spots to the Spothole system. Currently, spots added in this way are only visible within Spothole and are not sent "upstream" to DX clusters or xOTA spotting sites. The functionality might be extended to include this in future if there is demand for it. If you'd like this to be added, please give a thumbs-up on <a href="https://git.ianrenton.com/ian/spothole/issues/70" target="_new" class="alert-link">issue #70</a> or get in touch via email.
+  <button type="button" id="add-spot-intro-box-dismiss" class="btn-close" data-bs-dismiss="alert" aria-label="Close"></button>
+</div>
 </div>
 
 <div class="mt-3">
diff --git a/views/webpage_spots.tpl b/views/webpage_spots.tpl
index 3f79546..a152ca8 100644
--- a/views/webpage_spots.tpl
+++ b/views/webpage_spots.tpl
@@ -1,6 +1,6 @@
 % rebase('webpage_base.tpl')
 
-<div id="intro-box" class="mt-3">
+<div id="intro-box" class="permanently-dismissible-box mt-3">
 <div class="alert alert-primary alert-dismissible fade show" role="alert">
   <i class="fa-solid fa-circle-info"></i> <strong>What is Spothole?</strong><br/>Spothole is an aggregator of amateur radio spots from DX clusters and outdoor activity programmes. It's free for anyone to use and includes an API that developers can build other applications on. For more information, check out the <a href="/about" class="alert-link">"About" page</a>. If that sounds like nonsense to you, you can visit <a href="/about#faq" class="alert-link">the FAQ section</a> to learn more.
   <button type="button" id="intro-box-dismiss" class="btn-close" data-bs-dismiss="alert" aria-label="Close"></button>
diff --git a/webassets/apidocs/openapi.yml b/webassets/apidocs/openapi.yml
index 44858ac..691672f 100644
--- a/webassets/apidocs/openapi.yml
+++ b/webassets/apidocs/openapi.yml
@@ -493,7 +493,7 @@ paths:
       tags:
         - spots
       summary: Add a spot
-      description: "Supply a new spot object, which will be added to the system. Currently, this will not be reported up the chain to a cluster, POTA, SOTA etc. This will be introduced in a future version. cURL example: `curl --request POST --header \"Content-Type: application/json\" --data '{\"dx_call\":\"M0TRT\",\"time\":1760019539, \"freq\":14200000, \"comment\":\"Test spot please ignore\", \"de_call\":\"M0TRT\"}' https://spothole.app/api/v1/spot`"
+      description: "Supply a new spot object, which will be added to the system. Currently, this will not be reported up the chain to a cluster, POTA, SOTA etc. This may be introduced in a future version. cURL example: `curl --request POST --header \"Content-Type: application/json\" --data '{\"dx_call\":\"M0TRT\",\"time\":1760019539, \"freq\":14200000, \"comment\":\"Test spot please ignore\", \"de_call\":\"M0TRT\"}' https://spothole.app/api/v1/spot`"
       operationId: spot
       requestBody:
         description: The JSON spot object
diff --git a/webassets/css/style.css b/webassets/css/style.css
index 6e3777e..f3ae3a9 100644
--- a/webassets/css/style.css
+++ b/webassets/css/style.css
@@ -7,7 +7,7 @@
 
 /* INTRO/WARNING BOXES */
 
-#intro-box {
+.permanently-dismissible-box {
     display: none;
 }
 
diff --git a/webassets/js/add-spot.js b/webassets/js/add-spot.js
index e1ecc75..5d0c57a 100644
--- a/webassets/js/add-spot.js
+++ b/webassets/js/add-spot.js
@@ -48,7 +48,7 @@ function addSpot() {
                 }, 1000);
             },
             error: function (result) {
-                showAddSpotError(result.responseText);
+                showAddSpotError(result.responseText.slice(1,-1));
             }
         });
     } catch (error) {
@@ -73,8 +73,20 @@ $("#mode").change(function () {
     $(this).val($(this).val().trim().toUpperCase());
 });
 
+// Display the intro box, unless the user has already dismissed it once.
+function displayIntroBox() {
+    if (localStorage.getItem("add-spot-intro-box-dismissed") == null) {
+        $("#add-spot-intro-box").show();
+    }
+    $("#add-spot-intro-box-dismiss").click(function() {
+        localStorage.setItem("add-spot-intro-box-dismissed", true);
+    });
+}
+
 // Startup
 $(document).ready(function() {
     // Load settings from settings storage
     loadSettings();
+    // Display intro box
+    displayIntroBox();
 });
\ No newline at end of file