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**What you'll learn**

Through this tutorial, you'll learn to:

- See the response message's headers and body content.
- See error messages.

**What you'll need**

- At least one policy in your proxy (also part of the Get Started tutorial).
- [`curl`](https://curl.haxx.se/) installed on your machine to make API calls from the command line.

## View message data

The API proxy Trace tool lets you view headers, variables, objects, and other details such
as response time in the API proxy request and response flow. The Trace tool also lets you see
how a request or response changes as it is processed by an API proxy.

In [the previous tutorial](https://docs.apigee.com/api-platform/tutorials/add-spike-arrest), you restricted
the number of requests with the [SpikeArrest policy](https://docs.apigee.com/api-platform/reference/policies/spike-arrest-policy). Now, you'll use the Trace tool to see
interesting details when that rate is exceeded.

1. On the **Develop** tab of the API proxy, edit the Spike Arrest policy's `\<Rate\>` to be **1pm** again, then **Save** the proxy. This will allow us to see both successful and failed (over the limit) API calls.
2. In the API proxy editor, click the **Trace** tab.

   ![](https://docs.apigee.com/static/api-platform/images/trace_tab.png)
3. Click **Start Trace Session** .

   ![](https://docs.apigee.com/static/api-platform/images/trace_start_session.png)
4. Call the API proxy again using `curl` (or with the URL in a web browser) until you see
   at least one 200 response and one 429 response in the Transactions pane of Trace.

   ```
   curl "http://org_name-test.apigee.net/getstarted"
   ```

   ![](https://docs.apigee.com/static/api-platform/images/trace_helloworld_policies_transactions-1.png)

   > [!NOTE]
   > **NOTE:** The default HTTP status code for exceeding the rate limit is `429 Too many requests`.
   >
   > If you want the status code to be different (500, for example) for all Spike Arrest policies used in an
   > organization, a property needs to be set on your organization. If you're a Cloud customer,
   > contact [Apigee Edge Support](https://docs.apigee.com/api-platform/troubleshoot/support) to set that property.

5. Click **Stop Trace Session** .

   ![](https://docs.apigee.com/static/api-platform/images/trace_stop_session.png)
6. Click the **200** transaction in the left Transactions pane. Its Trace detail is loaded in the main window under Transaction Map, which shows a request/response diagram. The Spike Arrest icon is in the request flow.
7. In the flow diagram, click the **circle icon** in the response, the furthest one to the right (shown in the following diagram).

   The **Phase Details** pane shows the data available at that point in the
   flow. If you scroll through that pane, you'll see the HTTP response headers and body
   content.
8. Now look at an error in Trace. Click the **429** transaction in the Transactions pane. In the main editor
   window, you see a flow diagram with items in the request only, including a Spike Arrest
   icon with a red exclamation point indicating an error.

   Click the small tube **error icon** to the right of the Spike Arrest icon, and
   look at the spike arrest violation details in the **Phase Details** pane.

   ![Spike arrest error](https://docs.apigee.com/static/api-platform/images/trace_helloworld_policies_request_error_0.png)

You can click the **Back** and **Next** buttons in the flow
diagram to move between points in the flow and see the Trace details.

If you want to see the entire Trace as a single document, download it by clicking
**Download Trace Session**.

For more information, see [Using the Trace
tool](https://docs.apigee.com/api-platform/debug/using-trace-tool-0).