diff --git a/src/loaders/quilt/quilt-metadata-custom-payload.ts b/src/loaders/quilt/quilt-metadata-custom-payload.ts
new file mode 100644
index 0000000..c5bfb79
--- /dev/null
+++ b/src/loaders/quilt/quilt-metadata-custom-payload.ts
@@ -0,0 +1,123 @@
+import { ACTION_NAME } from "@/action";
+import { Dependency, createDependency } from "@/dependencies";
+import { LoaderType } from "@/loaders/loader-type";
+import { PlatformType } from "@/platforms";
+import { PartialRecord } from "@/utils/types";
+import { deprecate } from "node:util";
+import { RawQuiltMetadata } from "./raw-quilt-metadata";
+import { asString } from "@/utils/string-utils";
+
+// TODO: Remove the deprecated stuff in v4.0.
+
+/**
+ * Custom payload for Quilt metadata.
+ */
+export type QuiltMetadataCustomPayload = {
+    /**
+     * A list of supported mod loaders.
+     */
+    loaders?: string[];
+
+    /**
+     * A list of mod dependencies.
+     */
+    dependencies?: string[];
+}
+& PartialRecord<PlatformType, string>;
+
+/**
+ * Gets the custom payload from the Quilt metadata.
+ *
+ * @param metadata - The raw Quilt metadata.
+ *
+ * @returns The custom payload attached to the given metadata.
+ */
+export function getQuiltMetadataCustomPayload(metadata: RawQuiltMetadata): QuiltMetadataCustomPayload {
+    return containsLegacyCustomPayloadDefinition(metadata)
+        ? getLegacyQuiltMetadataCustomPayload(metadata)
+        : (metadata?.[ACTION_NAME] || {});
+}
+
+/**
+ * Checks if the metadata contains a legacy custom payload definition.
+ *
+ * @param metadata - The raw Quilt metadata.
+ *
+ * @returns A boolean indicating if the legacy custom payload definition is present.
+ */
+function containsLegacyCustomPayloadDefinition(metadata: RawQuiltMetadata): boolean {
+    return !!metadata?.projects;
+}
+
+/**
+ * Gets the legacy custom payload from the Quilt metadata.
+ *
+ * @param metadata - The raw Quilt metadata.
+ *
+ * @returns The custom payload object.
+ */
+function _getLegacyQuiltMetadataCustomPayload(metadata: RawQuiltMetadata): QuiltMetadataCustomPayload {
+    const legacyPayload = metadata?.projects;
+    const basePayload = metadata?.[ACTION_NAME];
+    return { ...legacyPayload, ...basePayload };
+}
+
+/**
+ * Gets the legacy custom payload from the Quilt metadata.
+ *
+ * @param metadata - The raw Quilt metadata.
+ *
+ * @returns The custom payload object.
+ *
+ * @deprecated
+ *
+ * Use top-level `mc-publish` field in your mod metadata.
+ */
+const getLegacyQuiltMetadataCustomPayload = deprecate(
+    _getLegacyQuiltMetadataCustomPayload,
+    "Use top-level `mc-publish` field in your quilt.mod.json.",
+);
+
+/**
+ * A list of default mod loaders associated with the Quilt loader.
+ */
+const DEFAULT_LOADERS = [LoaderType.QUILT] as const;
+
+/**
+ * Gets an array of supported mod loaders from the custom payload attached to the Quilt metadata.
+ *
+ * @param payload - The custom payload object.
+ *
+ * @returns An array of supported mod loaders.
+ */
+export function getLoadersFromQuiltMetadataCustomPayload(payload: QuiltMetadataCustomPayload): string[] {
+    return payload?.loaders || [...DEFAULT_LOADERS];
+}
+
+/**
+ * Gets the dependencies from the custom payload attached to the Quilt metadata.
+ *
+ * @param payload - The custom payload object.
+ *
+ * @returns An array of dependencies included into the custom payload.
+ */
+export function getDependenciesFromQuiltMetadataCustomPayload(payload: QuiltMetadataCustomPayload): Dependency[] {
+    if (!Array.isArray(payload?.dependencies)) {
+        return [];
+    }
+
+    return payload?.dependencies?.map(x => createDependency(x)).filter(x => x) || [];
+}
+
+/**
+ * Gets the project ID from the custom payload attached to the Quilt metadata based on the given platform.
+ *
+ * @param payload - The custom payload object.
+ * @param platform - The platform for which the project ID is required.
+ *
+ * @returns The project ID as a string, or `undefined` if not found.
+ */
+export function getProjectIdFromQuiltMetadataCustomPayload(payload: QuiltMetadataCustomPayload, platform: PlatformType): string | undefined {
+    const id = payload?.[platform];
+    return id ? asString(id) : undefined;
+}