JSON vs YAML vs XML: which one to pick?
A short rule for choosing, the same record in all three formats and the tools for validating each without uploading your files.
Use JSON to exchange data between programs, such as an API; YAML for config files a person reads and edits; and XML for documents with rich structure, strict validation or legacy systems. All three store the same information, and the choice comes down to who reads it and what you expect from it. To try any of them without uploading your files, you can format and validate JSON, format YAML or format XML in your browser.
One record, three formats
A person with a name, an age and two languages:
JSON:
{"name": "Ana", "age": 30, "languages": ["es", "en"]}YAML:
name: Ana
age: 30
languages:
- es
- enXML:
<person><name>Ana</name><age>30</age><languages><language>es</language><language>en</language></languages></person>The contrast is plain: JSON is compact, YAML looks like an outline written by hand, and XML repeats each tag name on opening and closing. Counting characters in the examples above, the JSON line takes 53, the YAML block 42 and the XML 115. Size isn't the main criterion, yet it explains why XML feels heavy for small records.
Side by side
| JSON | YAML | XML | |
|---|---|---|---|
| Comments | No | Yes, with # | Yes, with <!-- --> |
| Data types | String, number, boolean, null, array and object | The same, with inference rules | Everything is text unless a schema says otherwise |
| Human readability | Medium | High | Low in large documents |
| Size | Compact | Compact | Bulkier |
| Validation | Separate schemas | Separate schemas | XSD schemas and strict syntax checks |
| Typical use | APIs and data between systems | Config (compose files, CI) | Documents, feeds, legacy systems |
YAML 1.2 was designed as a superset of JSON, so nearly all valid JSON is also valid YAML. That makes switching straightforward, and the YAML tool has a YAML-to-JSON mode and a JSON-to-YAML mode.
When does each one fit?
- JSON when the consumer is a program and you want unambiguous structure. It's the format of most web APIs. If your JSON won't parse, the formatter points to the error by line and column. On handling data with third-party tools, see the privacy risk of online JSON formatters.
- YAML when a person will edit the file by hand and you need comments. Its weak spot is indentation and values that change type without warning, covered in YAML errors.
- XML when a document mixes text with structure, you need to validate against a strict schema, or you must interoperate with a system that already requires it. Sitemaps and many feeds are XML, and the XML tool formats and validates them. More in XML: structure, validation and common errors.
The mistakes each format invites - JSON: trailing commas, single quotes around strings and comments, none of which are allowed. - YAML: inconsistent indentation, tabs, and unquoted values such as NO or 1.10 that change type. - XML: tags that aren't closed or nested properly, and a bare & or < in text, which must be escaped. ## A word on safety Parsing is also where security problems hide. When you read YAML or XML from a source you don't control, use your library's safe loading mode. Some YAML libraries can build arbitrary objects from a document if you use their unsafe loader, and XML parsers can follow external entities unless configured not to. Check the documentation of the parser you use before feeding it untrusted files.
What about CSV?
For tabular data, CSV is usually the simplest. If you're torn between CSV and JSON, read CSV to JSON or JSON to CSV: which way and when.
Converting between formats
Between YAML and JSON the conversion is direct, and the tool does both directions. Remember that converting YAML to JSON drops comments, since JSON has no place for them. XML doesn't map one to one onto the other two, because of attributes and text mixed with tags, so the XML tool formats and validates but doesn't convert.
Familiar files, for reference
package.jsonandtsconfig.jsonare JSON.- Docker Compose files, GitHub Actions workflows and Kubernetes manifests are usually YAML.
sitemap.xml, RSS feeds and Office document internals are XML.
When a tool picks the format for you, follow it. Choosing only matters when you design a new file or API.
A short rule
If programs will read it, JSON. If a person will edit it, YAML. If the document needs strict structure or the other side already speaks XML, XML. And avoid mixing: pick one per kind of use inside a project.
Frequently asked questions
What is the difference between JSON, YAML and XML?
JSON is compact and used by APIs. YAML is more readable and supports comments, so it's used for configuration. XML is bulkier and stricter, and is used for documents and legacy systems.
When should I use YAML instead of JSON?
When a person will edit the file by hand and you want comments. For exchange between programs, JSON is safer, because YAML has type rules that can surprise you.
Is YAML the same as JSON?
YAML 1.2 is a superset of JSON, so nearly all valid JSON is valid YAML, but YAML adds comments, another syntax and its own type rules.
Can I convert JSON to YAML and back?
Yes, and the tool does both directions. Going from YAML to JSON drops the comments.
Is XML still used?
Yes, for documents with rich structure, strict validation and existing systems such as sitemaps and many feeds.
Are my files uploaded to a server?
No. The JSON, YAML and XML tools process in your browser.
Convert between YAML and JSON
Format, validate and convert YAML to JSON or JSON to YAML in your browser. Free, no signup.
Open YAML Formatter →Related tools
- JSON Formatter: validate and format, with errors by line and column.
- YAML Formatter: format and convert between YAML and JSON.
- XML Formatter: format and validate XML.
- CSV to JSON: turn tabular data into JSON.
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