diff --git a/mcp-gateway/wave-mcp/src/services/wave-client.ts b/mcp-gateway/wave-mcp/src/services/wave-client.ts
new file mode 100644
index 0000000..0e4eca2
--- /dev/null
+++ b/mcp-gateway/wave-mcp/src/services/wave-client.ts
@@ -0,0 +1,62 @@
+import { WaveConfig, GraphQLResponse } from "../types.js";
+import { WAVE_GRAPHQL_URL, CHARACTER_LIMIT } from "../constants.js";
+
+export class WaveClient {
+  private accessToken: string;
+
+  constructor(config: WaveConfig) {
+    this.accessToken = config.accessToken;
+  }
+
+  // ── Core GraphQL executor ──────────────────────────────────────────────────
+
+  async query<T = unknown>(
+    query: string,
+    variables?: Record<string, unknown>
+  ): Promise<T> {
+    const response = await fetch(WAVE_GRAPHQL_URL, {
+      method: "POST",
+      headers: {
+        Authorization: `Bearer ${this.accessToken}`,
+        "Content-Type": "application/json",
+        Accept: "application/json",
+      },
+      body: JSON.stringify({ query, variables: variables ?? {} }),
+    });
+
+    if (!response.ok) {
+      const text = await response.text().catch(() => "(no body)");
+      throw new Error(
+        `Wave API HTTP error ${response.status} ${response.statusText}: ${text.slice(0, 300)}`
+      );
+    }
+
+    const json = (await response.json()) as GraphQLResponse<T>;
+
+    if (json.errors?.length) {
+      const messages = json.errors.map((e) => e.message).join("; ");
+      throw new Error(`Wave GraphQL error: ${messages}`);
+    }
+
+    if (json.data === undefined) {
+      throw new Error("Wave API returned no data and no errors.");
+    }
+
+    return json.data;
+  }
+
+  // ── Formatting helpers ─────────────────────────────────────────────────────
+
+  /** Truncate a JSON response string if it exceeds CHARACTER_LIMIT */
+  static truncate(text: string): string {
+    if (text.length <= CHARACTER_LIMIT) return text;
+    return (
+      text.slice(0, CHARACTER_LIMIT) +
+      `\n\n...[TRUNCATED: response exceeded ${CHARACTER_LIMIT} characters. Use pagination (page, pageSize) to retrieve more data.]`
+    );
+  }
+
+  static formatCurrency(value: number, code: string): string {
+    return `${code} ${value.toFixed(2)}`;
+  }
+}