diff --git a/Libraries/SPTarkov.Server.Assets/SPT_Data/database/locales/server/en.json b/Libraries/SPTarkov.Server.Assets/SPT_Data/database/locales/server/en.json
index 2c3d87c9..feb67e91 100644
--- a/Libraries/SPTarkov.Server.Assets/SPT_Data/database/locales/server/en.json
+++ b/Libraries/SPTarkov.Server.Assets/SPT_Data/database/locales/server/en.json
@@ -62,6 +62,12 @@
   "chat-unable_to_register_command_already_registered": "Unable to register already registered command: %s",
   "client_request": "[Client Request] %s",
   "client_request_ip": "[Client Request] {{ip}} {{url}}",
+  "custom-quest-service_quest_id_already_exists": "A quest with the id: {{questId}} already exists.",
+  "custom-quest-service_no_languages_for_quest": "No languages have been added for custom quest id: {{questId}}",
+  "custom-quest-service_no_entries_for_language": "No locale entries have been added for language key: {{languageKey}}, was this intentional?",
+  "custom-quest-service_could_not_find_language_key": "Could not find language key: {{languageKey}} in global locales when adding a custom quest. This is either a typo, or this language is not supported.",
+  "custom-quest-service_locale_data_null": "Locale data is null for language: {{languageKey}}",
+  "custom-quest-service_invalid_side": "QuestId: {{questId}} Savage is not a valid side for a side locked quest.",
   "customisation-item_already_purchased": "Clothing item {{itemId}} {{itemName}} already purchased",
   "customisation-suit_lacks_upd_or_stack_property": "Suit with tpl: %s lacks a upd object or stackobjectcount property",
   "customisation-unable_to_find_clothing_item_in_inventory": "Clothing item not found in inventory with id: %s",
diff --git a/Libraries/SPTarkov.Server.Core/Models/Spt/Mod/NewQuestDetails.cs b/Libraries/SPTarkov.Server.Core/Models/Spt/Mod/NewQuestDetails.cs
new file mode 100644
index 00000000..e5ee3806
--- /dev/null
+++ b/Libraries/SPTarkov.Server.Core/Models/Spt/Mod/NewQuestDetails.cs
@@ -0,0 +1,49 @@
+using System.Text.Json.Serialization;
+using SPTarkov.Server.Core.Models.Common;
+using SPTarkov.Server.Core.Models.Eft.Common.Tables;
+using SPTarkov.Server.Core.Models.Enums;
+
+namespace SPTarkov.Server.Core.Models.Spt.Mod;
+
+/// <summary>
+///     New quest detail object for use with the CustomQuestService.
+/// </summary>
+public record NewQuestDetails
+{
+    /// <summary>
+    ///     Quest to be added to the database
+    /// </summary>
+    [JsonPropertyName("newQuest")]
+    public required Quest NewQuest { get; init; }
+
+    /// <summary>
+    ///     Locales for this quest. The primary key is the language to add to locale entries to<br/>
+    /// The secondary key is the locale key, the value is the locale text itself.
+    /// </summary>
+    [JsonPropertyName("locales")]
+    public required Dictionary<string, Dictionary<string, string>> Locales { get; init; }
+
+    /// <summary>
+    ///     Only Usec and Bear are valid entries here,
+    /// if used it will lock that quest to only being available to that specific side.<br/><br/>
+    ///
+    /// If not used, this should be left null to keep the quest open to both Usec and Bears.
+    /// </summary>
+    [JsonPropertyName("lockedToSide")]
+    public PlayerSide? LockedToSide { get; init; }
+}
+
+/// <summary>
+///     Result from either creating a new quest or cloning one.
+/// </summary>
+public record CreateQuestResult(bool Success, MongoId? QuestId)
+{
+    [JsonPropertyName("success")]
+    public bool Success { get; set; } = Success;
+
+    [JsonPropertyName("questId")]
+    public MongoId? QuestId { get; set; } = QuestId;
+
+    [JsonPropertyName("errors")]
+    public List<string> Errors { get; } = [];
+}
diff --git a/Libraries/SPTarkov.Server.Core/Services/Mod/CustomQuestService.cs b/Libraries/SPTarkov.Server.Core/Services/Mod/CustomQuestService.cs
new file mode 100644
index 00000000..230b96c9
--- /dev/null
+++ b/Libraries/SPTarkov.Server.Core/Services/Mod/CustomQuestService.cs
@@ -0,0 +1,121 @@
+using SPTarkov.DI.Annotations;
+using SPTarkov.Server.Core.Models.Common;
+using SPTarkov.Server.Core.Models.Enums;
+using SPTarkov.Server.Core.Models.Spt.Config;
+using SPTarkov.Server.Core.Models.Spt.Mod;
+using SPTarkov.Server.Core.Servers;
+
+namespace SPTarkov.Server.Core.Services.Mod;
+
+[Injectable]
+public class CustomQuestService(
+    DatabaseService databaseService,
+    ConfigServer configServer,
+    ServerLocalisationService serverLocalisationService
+)
+{
+    /// <summary>
+    ///     Create a new custom quest from a NewQuestDetails object.
+    /// </summary>
+    /// <param name="newQuestDetails">Quest details to be used for creation</param>
+    /// <returns>Result of the quest creation, remember to check it for errors!</returns>
+    public CreateQuestResult CreateQuest(NewQuestDetails newQuestDetails)
+    {
+        var quest = newQuestDetails.NewQuest;
+        var result = new CreateQuestResult(false, newQuestDetails.NewQuest.Id);
+
+        var databaseQuests = databaseService.GetTables().Templates.Quests;
+        if (!databaseQuests.TryAdd(quest.Id, quest))
+        {
+            result.Errors.Add(serverLocalisationService.GetText("custom-quest-service_quest_id_already_exists", quest.Id));
+            return result;
+        }
+
+        var locales = newQuestDetails.Locales;
+        if (locales.Count == 0)
+        {
+            result.Errors.Add(serverLocalisationService.GetText("custom-quest-service_no_languages_for_quest", quest.Id));
+            return result;
+        }
+
+        AddQuestLocales(locales, result);
+
+        var side = newQuestDetails.LockedToSide;
+        if (side.HasValue)
+        {
+            RestrictQuestSide(quest.Id, side.Value, result);
+        }
+
+        // No errors mean success
+        result.Success = result.Errors.Count == 0;
+        return result;
+    }
+
+    /// <summary>
+    ///     Adds quest locales to the database
+    /// </summary>
+    /// <param name="locales">locales to add</param>
+    /// <param name="result">create quest result</param>
+    private void AddQuestLocales(Dictionary<string, Dictionary<string, string>> locales, CreateQuestResult result)
+    {
+        var globalLocales = databaseService.GetLocales().Global;
+
+        foreach (var (languageKey, entries) in locales)
+        {
+            if (entries.Count == 0)
+            {
+                result.Errors?.Add(serverLocalisationService.GetText("custom-quest-service_no_entries_for_language", languageKey));
+                continue;
+            }
+
+            if (!globalLocales.TryGetValue(languageKey, out var lazyLoadedLocales))
+            {
+                result.Errors?.Add(serverLocalisationService.GetText("custom-quest-service_could_not_find_language_key", languageKey));
+                continue;
+            }
+
+            lazyLoadedLocales.AddTransformer(localeData =>
+            {
+                if (localeData is null)
+                {
+                    result.Errors?.Add(serverLocalisationService.GetText("custom-quest-service_locale_data_null", languageKey));
+                    return null;
+                }
+
+                foreach (var (key, entry) in entries)
+                {
+                    localeData.TryAdd(key, entry);
+                }
+
+                return localeData;
+            });
+        }
+    }
+
+    /// <summary>
+    ///     Restricts a custom quest to a specific side.
+    /// </summary>
+    /// <param name="questId">Quest id to restrict</param>
+    /// <param name="side">Side to restrict it to</param>
+    /// <param name="result">Result of the quest creation</param>
+    private void RestrictQuestSide(MongoId questId, PlayerSide side, CreateQuestResult result)
+    {
+        var questConfig = configServer.GetConfig<QuestConfig>();
+
+        // ReSharper disable once SwitchStatementHandlesSomeKnownEnumValuesWithDefault
+        switch (side)
+        {
+            case PlayerSide.Usec:
+                questConfig.UsecOnlyQuests.Add(questId);
+                break;
+
+            case PlayerSide.Bear:
+                questConfig.BearOnlyQuests.Add(questId);
+                break;
+
+            case PlayerSide.Savage:
+                result.Errors.Add(serverLocalisationService.GetText("custom-quest-service_invalid_side", result.QuestId));
+                break;
+        }
+    }
+}