Which format is the most used today?

JSON dominates the web, no question. It is the default for REST APIs and frontend configuration. YAML rules DevOps and infrastructure, especially CI pipelines and container definitions. XML still holds ground in enterprise environments and formats with complex document structure. TOML grew significantly in developer tooling ecosystems. CSV remains the standard for tabular data.

Can I convert between formats?

Yes, in most cases. JSON, YAML and TOML have similar data models and conversion between them is almost direct. XML is more complex because of attributes and mixed content, but there are common mappings. CSV only represents tables, so converting to hierarchical or from hierarchical to CSV requires decisions on how to flatten the structure.

Why is YAML so problematic?

It has a much larger specification than it looks. Some keywords ("yes", "no", "on", "off") are interpreted as booleans, numbers with leading zeros may be read as octal, and indentation with spaces or tabs causes silent errors. Newer versions (YAML 1.2) addressed some of these, but you need to be careful about the parser's strict mode.

Do JSON5 and JSONC solve JSON's lack of comments?

Yes, they are JSON variants that add comments and some extra flexibility (trailing commas, unquoted keys). They are not universal standards but are supported in specific environments like code editors. For exchange between systems, stick to plain JSON for guaranteed compatibility.

When should I pick TOML over YAML?

TOML is better when you want clean syntax for configuration without YAML's indentation traps. For project configuration files with medium structure, TOML tends to be less error prone. YAML is better for very deep structures or when you need internal references and advanced features.

Data Format Comparison. JSON, YAML, XML, TOML, INI, CSV

Comparison table

Format	Comments	Verbosity	Types	Human readable	Typical use
JSON .json	No	Medium	Basic	Medium	Web APIs, frontend config
YAML .yaml / .yml	Yes	Low	Basic	High	CI/CD pipelines, infrastructure as code
XML .xml	Yes	High	Text only	Low	Enterprise systems, documents, SOAP
TOML .toml	Yes	Medium	Rich	High	Application config, developer tooling
INI .ini / .conf	Yes	Low	Text only	High	Simple configuration, legacy files
CSV .csv	No	Low	Tabular	Medium	Spreadsheets, tabular data export

Format by format

JSON.json

JavaScript Object Notation

Format derived from JavaScript object syntax. It became the lingua franca for data exchange on the web thanks to its simplicity and native support in every modern language.

Example

{
  "server": {
    "host": "localhost",
    "port": 8080,
    "debug": false,
    "tags": ["web", "api"]
  }
}

Pros

+Natively supported by virtually every language
+Simple and predictable syntax
+Fast and cheap to parse
+Clear hierarchical structure

Cons

−No comment support, which hurts hand-edited configuration files
−Unforgiving of syntax mistakes (one trailing comma and parse fails)
−Verbose for long configuration due to mandatory quotes and braces

When to use

REST API requests and responses, structured data storage, communication between services. Anywhere human readability is secondary to interoperability.

YAML.yaml / .yml

YAML Ain't Markup Language

Format built for human readability, with indentation based syntax instead of braces. It is a superset of JSON.

Example

server:
  host: localhost
  port: 8080
  debug: false
  tags:
    - web
    - api

Pros

+Very readable, no visual noise from braces and quotes
+Supports comments and internal references
+Great for hand edited files
+Complex structures with minimal syntax

Cons

−Significant indentation is a common source of bugs (tabs vs spaces)
−Large spec with surprising edge cases ("yes" and "no" parsed as booleans)
−Slower parsing and reliant on external libraries in some languages

When to use

CI/CD pipelines, container definitions, orchestrator configuration, and any long configuration file that benefits from comments and clear structure.

XML.xml

Extensible Markup Language

Tag based format with roots in SGML. For years it was the default for structured data exchange before JSON took over.

Example

<server>
  <host>localhost</host>
  <port>8080</port>
  <debug>false</debug>
  <tags>
    <tag>web</tag>
    <tag>api</tag>
  </tags>
</server>

Pros

+Mature formal schemas (XSD, DTD) for strict validation
+Strong metadata support through attributes and namespaces
+Powerful ecosystem of transformations with XSLT and queries with XPath
+Ideal for documents with mixed content (text and structure)

Cons

−Very verbose, opening and closing tags double the bulk
−The distinction between attributes and elements is arbitrary and divisive
−Harder to read and write by hand than modern alternatives

When to use

Integrations with legacy or enterprise systems, documents with complex structure, formats where rigorous schema validation is required (electronic invoicing, office files).

TOML.toml

Tom's Obvious Minimal Language

Relatively recent format, designed to be obvious and unambiguous. Combines INI style sections with rich data types and support for nested structures.

Example

[server]
host = "localhost"
port = 8080
debug = false
tags = ["web", "api"]

Pros

+Short specification with no ambiguous cases
+Native types for dates, numbers and arrays
+Supports comments and named sections
+Balance between human readability and reliable parsing

Cons

−Less universal, outside of the ecosystems that adopted it can feel exotic
−Deeply nested structures become more verbose than in YAML
−Growing community, fewer auxiliary tools

When to use

Modern project configuration files, package manifests, any case where you want clean syntax without YAML's indentation pitfalls.

INI.ini / .conf

Initialization File

One of the oldest formats still in use. Structured around bracketed sections and key value pairs. There is no single formal specification, which creates incompatible variants.

Example

[server]
host = localhost
port = 8080
debug = false
tags = web,api

Pros

+Extremely simple to read and write
+Trivial to parse, even with your own code
+Supported by many operating systems and tools
+Accepts comments and sections

Cons

−No formal standard, every implementation differs
−No deep hierarchy beyond a single section
−All values are strings, type conversion is up to the application
−No native support for structured lists

When to use

Flat configuration for small tools, user files on Windows and Linux systems, cases where simplicity beats features.

CSV.csv

Comma-Separated Values

Format for tabular data: one row per record, values separated by commas. It has been around for decades and remains the bread and butter of exchange between spreadsheets, databases and analytics tools.

Example

host,port,debug,tags
localhost,8080,false,"web,api"
example.com,443,true,"web"

Pros

+Universal across spreadsheets, databases and statistical tools
+Compact for purely tabular data
+Line by line streaming makes huge files tractable
+Editable in any tool, from Excel to Vim

Cons

−No hierarchy, just a flat table
−No types, everything is a string with no distinction between number and text
−Handling quotes, commas inside values and line breaks is a classic source of bugs
−Regional variations (comma vs semicolon as separator)

When to use

Report export, spreadsheet import, datasets for statistical analysis, any scenario where the data is genuinely tabular.

About this tool

Direct comparison between six widely used data serialization formats: JSON, YAML, XML, TOML, INI and CSV. For each one you get side by side syntax, strengths, weaknesses and the context in which it makes sense to pick it. Useful for deciding the configuration format of a new application, quickly getting up to speed on a format you have not used before, or backing a technical decision with concrete reasoning.

How to use

Read the comparison table for an overview of each format's traits.
Compare the examples side by side. They all represent the same object to make comparison easier.
Decide based on context. Some formats are better for hand edited configuration, others for exchange between systems.

Frequently asked questions

Which format is the most used today?: JSON dominates the web, no question. It is the default for REST APIs and frontend configuration. YAML rules DevOps and infrastructure, especially CI pipelines and container definitions. XML still holds ground in enterprise environments and formats with complex document structure. TOML grew significantly in developer tooling ecosystems. CSV remains the standard for tabular data.
Can I convert between formats?: Yes, in most cases. JSON, YAML and TOML have similar data models and conversion between them is almost direct. XML is more complex because of attributes and mixed content, but there are common mappings. CSV only represents tables, so converting to hierarchical or from hierarchical to CSV requires decisions on how to flatten the structure.
Why is YAML so problematic?: It has a much larger specification than it looks. Some keywords ("yes", "no", "on", "off") are interpreted as booleans, numbers with leading zeros may be read as octal, and indentation with spaces or tabs causes silent errors. Newer versions (YAML 1.2) addressed some of these, but you need to be careful about the parser's strict mode.
Do JSON5 and JSONC solve JSON's lack of comments?: Yes, they are JSON variants that add comments and some extra flexibility (trailing commas, unquoted keys). They are not universal standards but are supported in specific environments like code editors. For exchange between systems, stick to plain JSON for guaranteed compatibility.
When should I pick TOML over YAML?: TOML is better when you want clean syntax for configuration without YAML's indentation traps. For project configuration files with medium structure, TOML tends to be less error prone. YAML is better for very deep structures or when you need internal references and advanced features.

JSON vs YAML vs XML vs TOML vs INI vs CSV

About this tool

How to use

Frequently asked questions

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