Increase character limit to 5000 using instructions from https://draklyckan.se/2021/11/how-to-increase-the-character-limit-for-toots-in-mastodon/

app/javascript/mastodon/features/compose/components/compose_form.jsx

@@ -100,8 +100,8 @@ class ComposeForm extends ImmutablePureComponent {
     const fulltext = this.getFulltextForCharacterCounting();
     const isOnlyWhitespace = fulltext.length !== 0 && fulltext.trim().length === 0;
 
-    return !(isSubmitting || isUploading || isChangingUpload || length(fulltext) > 500 || (isOnlyWhitespace && !anyMedia));
-  };
+    return !(isSubmitting || isUploading || isChangingUpload || length(fulltext) > 5000 || (isOnlyWhitespace && !anyMedia));
+  }
 
   handleSubmit = (e) => {
     if (this.props.text !== this.autosuggestTextarea.textarea.value) {
@@ -296,9 +296,8 @@ class ComposeForm extends ImmutablePureComponent {
               <LanguageDropdown />
             </div>
 
-            <div className='character-counter__wrapper'>
-              <CharacterCounter max={500} text={this.getFulltextForCharacterCounting()} />
-            </div>
+          <div className='character-counter__wrapper'>
+            <CharacterCounter max={5000} text={this.getFulltextForCharacterCounting()} />
           </div>
         </div>
 

app/serializers/rest/instance_serializer.rb

@@ -9,9 +9,12 @@ class REST::InstanceSerializer < ActiveModel::Serializer
 
   include RoutingHelper
 
-  attributes :domain, :title, :version, :source_url, :description,
-             :usage, :thumbnail, :languages, :configuration,
-             :registrations
+  attributes :uri, :title, :short_description, :description, :email,
+             :version, :urls, :stats, :thumbnail,
+             :languages, :registrations, :max_toot_chars, :approval_required, :invites_enabled,
+             :configuration
+
+  has_one :contact_account, serializer: REST::AccountSerializer
 
   has_one :contact, serializer: ContactSerializer
   has_many :rules, serializer: REST::RuleSerializer
@@ -89,6 +92,10 @@ class REST::InstanceSerializer < ActiveModel::Serializer
     }
   end
 
+  def max_toot_chars
+    5000
+  end
+
   private
 
   def registrations_enabled?

app/validators/status_length_validator.rb

@@ -1,7 +1,7 @@
 # frozen_string_literal: true
 
 class StatusLengthValidator < ActiveModel::Validator
-  MAX_CHARS = 500
+  MAX_CHARS = 5000
   URL_PLACEHOLDER_CHARS = 23
   URL_PLACEHOLDER = 'x' * 23