diff --git a/CHANGELOG.md b/CHANGELOG.md
index 74e420c..b6eaeee 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -5,6 +5,12 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.1.0/),
 and this project follows [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## [0.0.83] - 2026-07-20
+
+### Fixed
+
+- Query params that are plain objects (including `p.json()` values) are now JSON-serialized instead of becoming `"[object Object]"` via `String(value)`. Pre-stringified JSON strings and primitive params are unchanged.
+
 ## [0.0.82] - 2026-07-15
 
 ### Changed
diff --git a/package.json b/package.json
index 69b1a1d..5b56ee5 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "@tinybirdco/sdk",
-  "version": "0.0.82",
+  "version": "0.0.83",
   "description": "TypeScript SDK for Tinybird Forward - define datasources and pipes as TypeScript",
   "type": "module",
   "main": "./dist/index.js",
diff --git a/src/api/api.test.ts b/src/api/api.test.ts
index 2480cec..44d45cc 100644
--- a/src/api/api.test.ts
+++ b/src/api/api.test.ts
@@ -142,6 +142,69 @@ describe("TinybirdApi", () => {
     ).rejects.toThrow("Date values are not supported for query parameter");
   });
 
+  it("JSON-stringifies plain object query params (p.json())", async () => {
+    let configOverridesParam: string | null = null;
+    let preStringifiedParam: string | null = null;
+    let objectArrayParams: string[] = [];
+    let limitParam: string | null = null;
+    let tagsParams: string[] = [];
+
+    server.use(
+      http.get(`${BASE_URL}/v0/pipes/json_echo.json`, ({ request }) => {
+        const url = new URL(request.url);
+        configOverridesParam = url.searchParams.get("configOverrides");
+        preStringifiedParam = url.searchParams.get("preStringified");
+        objectArrayParams = url.searchParams.getAll("items");
+        limitParam = url.searchParams.get("limit");
+        tagsParams = url.searchParams.getAll("tags");
+
+        return HttpResponse.json({
+          data: [{ key_count: 1 }],
+          meta: [{ name: "key_count", type: "UInt64" }],
+          rows: 1,
+          statistics: {
+            elapsed: 0.001,
+            rows_read: 1,
+            bytes_read: 10,
+          },
+        });
+      })
+    );
+
+    const api = createTinybirdApi({
+      baseUrl: BASE_URL,
+      token: "p.default-token",
+    });
+
+    await api.query("json_echo", {
+      configOverrides: { foo: 1 },
+      preStringified: '{"foo":1}',
+      items: [{ a: 1 }, { b: 2 }],
+      limit: 5,
+      tags: ["a", "b"],
+    });
+
+    expect(configOverridesParam).toBe('{"foo":1}');
+    expect(configOverridesParam).not.toBe("[object Object]");
+    expect(preStringifiedParam).toBe('{"foo":1}');
+    expect(objectArrayParams).toEqual(['{"a":1}', '{"b":2}']);
+    expect(limitParam).toBe("5");
+    expect(tagsParams).toEqual(["a", "b"]);
+  });
+
+  it("throws when array query params include Date values", async () => {
+    const api = createTinybirdApi({
+      baseUrl: BASE_URL,
+      token: "p.default-token",
+    });
+
+    await expect(
+      api.query("top_pages", {
+        tags: [new Date("2024-01-01T00:00:00.000Z")],
+      })
+    ).rejects.toThrow("Date values are not supported for query parameter");
+  });
+
   it("ingests rows via tinybirdApi.ingest", async () => {
     let datasourceName: string | null = null;
     let waitParam: string | null = null;
diff --git a/src/api/api.ts b/src/api/api.ts
index dab93fe..53b9230 100644
--- a/src/api/api.ts
+++ b/src/api/api.ts
@@ -17,6 +17,26 @@ const DEFAULT_TIMEOUT = 30000;
 const DEFAULT_INGEST_RETRY_503_BASE_DELAY_MS = 200;
 const DEFAULT_INGEST_RETRY_503_MAX_DELAY_MS = 3000;
 
+/**
+ * Serialize a single query-param value for the Tinybird pipes API.
+ * Plain objects (e.g. p.json() params) become JSON strings; Dates are rejected;
+ * everything else uses String(value).
+ */
+function serializeQueryParamValue(key: string, value: unknown): string {
+  if (value instanceof Date) {
+    throw new Error(
+      `Date values are not supported for query parameter "${key}". ` +
+        "Pass a string in YYYY-MM-DD HH:MM:SS format (or YYYY-MM-DD HH:MM:SS.sss for DateTime64)."
+    );
+  }
+
+  if (typeof value === "object" && value !== null && !Array.isArray(value)) {
+    return JSON.stringify(value);
+  }
+
+  return String(value);
+}
+
 /**
  * Public, decoupled Tinybird API wrapper configuration
  */
@@ -214,25 +234,12 @@ export class TinybirdApi {
 
       if (Array.isArray(value)) {
         for (const item of value) {
-          if (item instanceof Date) {
-            throw new Error(
-              `Date values are not supported for query parameter "${key}". ` +
-                "Pass a string in YYYY-MM-DD HH:MM:SS format (or YYYY-MM-DD HH:MM:SS.sss for DateTime64)."
-            );
-          }
-          url.searchParams.append(key, String(item));
+          url.searchParams.append(key, serializeQueryParamValue(key, item));
         }
         continue;
       }
 
-      if (value instanceof Date) {
-        throw new Error(
-          `Date values are not supported for query parameter "${key}". ` +
-            "Pass a string in YYYY-MM-DD HH:MM:SS format (or YYYY-MM-DD HH:MM:SS.sss for DateTime64)."
-        );
-      }
-
-      url.searchParams.set(key, String(value));
+      url.searchParams.set(key, serializeQueryParamValue(key, value));
     }
 
     const response = await this.request(url.toString(), {