diff --git a/plugin/core/config.ts b/plugin/core/config.ts
new file mode 100644
index 0000000..1d2e9b0
--- /dev/null
+++ b/plugin/core/config.ts
@@ -0,0 +1,67 @@
+export interface YonexusClientConfig {
+  mainHost: string;
+  identifier: string;
+  notifyBotToken: string;
+  adminUserId: string;
+}
+
+export class YonexusClientConfigError extends Error {
+  readonly issues: string[];
+
+  constructor(issues: string[]) {
+    super(`Invalid Yonexus.Client config: ${issues.join("; ")}`);
+    this.name = "YonexusClientConfigError";
+    this.issues = issues;
+  }
+}
+
+function isNonEmptyString(value: unknown): value is string {
+  return typeof value === "string" && value.trim().length > 0;
+}
+
+function isValidWsUrl(value: string): boolean {
+  try {
+    const url = new URL(value);
+    return url.protocol === "ws:" || url.protocol === "wss:";
+  } catch {
+    return false;
+  }
+}
+
+export function validateYonexusClientConfig(raw: unknown): YonexusClientConfig {
+  const source = raw as Record<string, unknown> | null;
+  const issues: string[] = [];
+
+  const mainHost = source?.mainHost;
+  if (!isNonEmptyString(mainHost)) {
+    issues.push("mainHost is required");
+  } else if (!isValidWsUrl(mainHost.trim())) {
+    issues.push("mainHost must be a valid ws:// or wss:// URL");
+  }
+
+  const identifier = source?.identifier;
+  if (!isNonEmptyString(identifier)) {
+    issues.push("identifier is required");
+  }
+
+  const notifyBotToken = source?.notifyBotToken;
+  if (!isNonEmptyString(notifyBotToken)) {
+    issues.push("notifyBotToken is required");
+  }
+
+  const adminUserId = source?.adminUserId;
+  if (!isNonEmptyString(adminUserId)) {
+    issues.push("adminUserId is required");
+  }
+
+  if (issues.length > 0) {
+    throw new YonexusClientConfigError(issues);
+  }
+
+  return {
+    mainHost: mainHost.trim(),
+    identifier: identifier.trim(),
+    notifyBotToken: notifyBotToken.trim(),
+    adminUserId: adminUserId.trim()
+  };
+}
diff --git a/plugin/index.ts b/plugin/index.ts
index 8a095cd..28b2420 100644
--- a/plugin/index.ts
+++ b/plugin/index.ts
@@ -1,3 +1,6 @@
+export { validateYonexusClientConfig, YonexusClientConfigError } from "./core/config.js";
+export type { YonexusClientConfig } from "./core/config.js";
+
 export interface YonexusClientPluginManifest {
   readonly name: "Yonexus.Client";
   readonly version: string;