YAML vs TOML — Which Config Format Should You Use?

YAML and TOML both aim to be human-readable configuration formats. YAML is more expressive and widely supported; TOML is simpler, more explicit, and harder to get wrong. The choice often comes down to your tooling and how complex your config is.

Use the YAML to JSON Converter to validate and convert YAML configurations.

TOML vs YAML: a direct comparison

The same configuration in both formats:

TOML:

[database]
host = "localhost"
port = 5432
name = "myapp"

[database.pool]
min = 5
max = 20
timeout = 30

[[servers]]
host = "10.0.0.1"
role = "primary"

[[servers]]
host = "10.0.0.2"
role = "replica"

YAML equivalent:

database:
  host: localhost
  port: 5432
  name: myapp
  pool:
    min: 5
    max: 20
    timeout: 30

servers:
  - host: 10.0.0.1
    role: primary
  - host: 10.0.0.2
    role: replica

Both parse to the same data structure. The differences show in the syntax choices.

TOML strengths

Explicit types

TOML has explicit type syntax — there’s no ambiguity:

string = "hello"
integer = 42
float = 3.14
boolean = true
date = 2026-05-11T10:00:00Z
array = [1, 2, 3]

Compare to YAML, where yes, true, on all parse as booleans in YAML 1.1:

# YAML 1.1 implicit boolean:
active: yes      # true
enabled: true    # true
on: on           # true!

# This bit people:
country: NO      # Parsed as false in YAML 1.1 (Norway!)

TOML never has this problem.

Clear table (object) syntax

TOML sections are unambiguous:

[server]
host = "localhost"
port = 8080

[server.tls]
enabled = true
cert = "/etc/ssl/cert.pem"

No indentation sensitivity — you can’t accidentally un-nest a section by wrong indentation.

Array of tables

[[routes]]
path = "/home"
handler = "homeHandler"

[[routes]]
path = "/api/users"
handler = "usersHandler"
methods = ["GET", "POST"]

Each [[routes]] entry appends to the array — clear and explicit.

YAML strengths

Anchors and aliases

YAML can reuse values; TOML has no equivalent:

defaults: &defaults
  timeout: 30
  retries: 3

service_a:
  <<: *defaults
  host: "service-a.internal"

service_b:
  <<: *defaults
  host: "service-b.internal"
  timeout: 60  # override

Multiline strings

YAML handles multiline content cleanly:

description: |
  This service handles user authentication
  and session management.

script: |
  #!/bin/bash
  set -e
  npm install
  npm test

TOML multiline strings exist but are less elegant:

script = """
#!/bin/bash
set -e
npm install
npm test
"""

Industry adoption

YAML is the dominant format in:

• Kubernetes (kind: Deployment, etc.)
• Docker Compose (docker-compose.yml)
• GitHub Actions (.github/workflows/)
• Ansible playbooks
• Helm charts
• OpenAPI specifications

If your tooling expects YAML, you don’t have a choice.

TOML adoption

TOML is dominant in:

• Rust: Cargo.toml (package manifest)
• Python: pyproject.toml (PEP 517/518 packaging)
• Hugo: config.toml (static site generator)
• Gitea/Forgejo: app.ini-like configs
• TOML-enabled apps: many modern CLI tools

Syntax comparison

Feature	YAML	TOML
Strings	key: value or key: "value"	key = "value" (always quoted)
Nested objects	Indentation	[section.subsection]
Arrays	- item or [item]	[item]
Multiline	`	or>` block scalars
Anchors/aliases	Yes (&, *)	No
Comments	# comment	# comment
Ambiguous values	Yes (many!)	No (explicit types)
Spec version issues	YAML 1.1 vs 1.2	One spec, clear

Common YAML footguns (TOML avoids)

# These are all valid YAML and may surprise you:
port: 8080     # integer
host: localhost # string
debug: yes     # boolean true (YAML 1.1)
version: 1.0   # float (not string "1.0"!)
date: 2026-05  # date-like string OR date?

# Norway problem:
country: NO    # boolean false in YAML 1.1!

# Octal numbers in YAML 1.1:
mode: 0755     # parsed as octal integer 493!

TOML requires explicit quoting for strings — you can’t accidentally get a type wrong.

When to choose YAML

• Your tooling requires YAML (Kubernetes, GitHub Actions, Docker Compose)
• You need anchors/aliases for DRY configs
• Your team is already comfortable with YAML
• You have complex nested structures with many levels

When to choose TOML

• You’re writing a Rust or Python project (Cargo.toml, pyproject.toml)
• You want to avoid YAML’s type ambiguity
• Your config is relatively flat
• You want a simpler, easier to explain format
• You’re building a new tool and choosing a config format from scratch

Related tools

• YAML to JSON Converter — validate and convert YAML
• YAML Syntax Guide — complete YAML reference
• YAML vs JSON — another format comparison