Development
YAML Viewer & API Tester
Open YAML files such as docker-compose.yml, GitHub workflows or Kubernetes manifests, find errors with line numbers and explanations, and convert them to JSON. If the file contains an OpenAPI or Swagger description, you can test the endpoints directly.
- Runs entirely in your browser
- No data upload
- No sign-up
- Free
YAML
View
$
Consistently formatted: 2 or 4 spaces, anchors and aliases are kept. Comments (# …) are dropped.
Anchors, aliases and merge keys (<<) are resolved in JSON.
Test the API
API description
Credentials
Credentials stay only in this browser tab and are not stored anywhere. They are only sent to the API with your test request.
Test requests are sent only on click and directly from your browser to the API entered – not via gutowski.org. If the API does not respond, it usually blocks requests from other websites (CORS); then the curl command helps.
Guide
How it works
- Load YAML
Paste YAML (or JSON) into the left field, drag in a .yaml or .yml file or open it via “Open file”. There are three examples to try out.
- Find errors
The tool checks instantly. In case of an error, you see the line, column and an explanation – for example about tabs, wrong indentation or a missing colon. Notes point out typical pitfalls such as “no” or “22:22”.
- View and convert
In the tree view you expand the structure and copy the path to every value. Under “YAML” the file is consistently formatted, under “JSON” it is shown as JSON – to copy or download.
- Test the API
If the file is an OpenAPI or Swagger description, the API tester appears below: choose an endpoint, fill in parameters and body, click “Send request” – and view the status, response time, headers and response. The matching curl command is included.
FAQ
Frequently asked questions
Are my files uploaded?
No. The YAML file is only read in your browser. Test requests do not go through gutowski.org either: they are only sent on click, directly from your browser to the API you are testing.
Why do I get no response from some APIs?
Browsers protect you with a rule called CORS: a website may only read the response of another API if the API explicitly allows it (header Access-Control-Allow-Origin). Many public APIs and development servers do, others do not. In that case, copy the curl command and run it in the terminal – CORS does not apply there.
Which API descriptions are supported?
OpenAPI 3.0 and 3.1 as well as Swagger 2.0, each as YAML or JSON. References within the file ($ref) are resolved; references to other files are not loaded.
Why is a tab an error?
YAML defines the structure through indentation and only allows spaces for it. However, many editors insert a tab character when you press the Tab key. The tool shows the position; in the input field here, the Tab key automatically inserts two spaces.
What do the notes about “yes”, “no” or “22:22” mean?
The current version YAML 1.2 reads “no” as a string and 22:22 as a string. Older parsers following YAML 1.1 – for example PyYAML in Python – turn them into false or the number 1342. To be on the safe side, put such values in quotes.
What happens to anchors (&) and aliases (*)?
They are kept in the tree view and the formatted YAML output. For JSON they are resolved because JSON has no references – as are merge keys (<<: *defaults), as often found in docker-compose files.
Are my credentials stored?
No. API keys, tokens and passwords remain only in the memory of this browser tab and are only sent to the API with your test request. After closing the page they are gone. That is also why there is deliberately no “Share link”.