Priorities tailored to each symptom
For a 401, start with credentials. For a 403, check permissions and API access approval. For CORS, inspect the response headers first. The most relevant checks move to the top.
Free interactive diagnosis—no signup required
Turn API errors into a clear troubleshooting checklist.
Built for developers and operations teams blocked by an API integration. Select the service, symptoms, and response code to instantly create a prioritized checklist covering everything from credentials to response data.
Start a free diagnosis ↓
Free, no signup required, and all data is processed on your device. You can download a practical template without entering any details.
● Isolate causes in priority order
Interactive diagnosis
Diagnose the cause of your API connection error
Select only what you know. The tool uses the symptoms and HTTP status to build a prioritized investigation plan with specific checks.
Your diagnosis will appear here
Complete the fields on the left to get troubleshooting steps organized in priority order.
Diagnosis results
Free, with no signup required. Saved data stays only in this device's browser and is never sent externally.
Your file has been saved. Next, work through the checklist from the top and mark each completed item.
0
areas checked to isolate the cause
0
ways to save, copy, or export
0
input data sent externally
Why it works
Replace random searching with repeatable troubleshooting
Check commonly overlooked prerequisites in order before searching every error message. Keep a reusable record for handoffs and preventing repeat incidents.
A checklist you can revisit
Mark items as you complete them during the investigation. Reduce missed checks and make it easier to show the next person exactly how far the investigation has progressed.
Ready-to-use Markdown export
Organize your inputs, diagnostic summary, troubleshooting steps, and completion status in one file. Use it in issues, internal wikis, chats, or incident records.
3 steps
Create an API troubleshooting plan in three steps
You can get started even if you do not know every technical configuration value.
01
Select the service and symptom
Enter the destination name, the symptom you are seeing, and the HTTP response code if available.
02
Check items in priority order
Work through the displayed steps from the top. Check off completed items to keep a record of your progress.
03
Save and share the results
Save the diagnosis in your browser or download the Markdown file for incident records and handoffs.
FAQ
Frequently asked questions about API connection troubleshooting
Is the API information I enter sent externally?
No. The diagnosis runs in the browser displaying this page. If you choose browser storage, the data is saved in local storage on this device. For security, however, do not enter actual secret keys or access tokens.
What is the difference between 401 and 403?
Generally, 401 means the credentials could not be authenticated, while 403 means authentication succeeded but the account lacks permission to perform the operation. Implementations vary by API, so also check the error definitions in the official documentation.
Can changing the API key fix a CORS error?
Usually, changing the API key alone will not fix it. Check the browser origin, preflight request, response headers such as Access-Control-Allow-Origin, and whether the API permits direct browser access.
Can I run a diagnosis without a response code?
Yes. Select “Unknown or unavailable.” The tool will prioritize checks along the connection path before an HTTP response is reached, including DNS, TLS, proxies, firewalls, and timeouts.
Can the diagnosis identify the definitive cause of an incident?
This tool organizes likely causes and helps reduce missed checks. To confirm the cause, also review the API's official documentation, status page, request logs, and response body.
How long do saved diagnosis results remain available?
They remain until the browser's local storage is cleared. Data may disappear when you close private browsing, reset browser settings, or switch devices, so save important records as Markdown too.
Prepare for your next API error
with a practical checklist
Even without running a diagnosis, you can immediately download a Markdown template covering authentication, API access approval, endpoints, permissions, CORS, connectivity, and response data.
Free, no signup, and no email address required. Click to download directly to your device.