YAML to TOML Converter

YAML to TOML: Converting Config Files Between Formats

TOML (Tom's Obvious Minimal Language) was designed as a simpler, more readable alternative to YAML for configuration files. Where YAML relies on significant whitespace and implicit types, TOML uses explicit section headers and clear type syntax. TOML is the native format for Rust's Cargo.toml, Python's pyproject.toml, and Hugo static sites — and it's becoming the default for new tooling because it's unambiguous and trivial to parse.

Live Example: Service Configuration

# Input YAML
server:
  host: "api.example.com"
  port: 8080
  tls: true

database:
  url: "postgres://localhost/mydb"
  pool_size: 10
  timeout_seconds: 30

features:
  enable_cache: true
  cache_ttl: 3600
  allowed_origins:
    - "https://app.example.com"
    - "https://admin.example.com"

# Generated TOML
# TOML configuration format

[server]
host = "api.example.com"
port = 8080
tls = true

[database]
url = "postgres://localhost/mydb"
pool_size = 10
timeout_seconds = 30

[features]
enable_cache = true
cache_ttl = 3600
allowed_origins = ["https://app.example.com", "https://admin.example.com"]

TOML Type System: What Changes from YAML

YAML's implicit type coercion is its biggest pain point. TOML is explicit:

# YAML gotchas (these are all valid YAML with surprising types)
enabled: yes          # Boolean true — but looks like a string
count: 1_000          # Integer 1000 — underscore separator
api_key: 0001         # Integer 1, not string "0001"
created: 2024-01-15   # Date object, not string
norway: NO            # Boolean false (old YAML 1.1 spec!)

# TOML equivalents — unambiguous
enabled = true          # Boolean literal: true or false only
count = 1_000           # Still valid: integer with underscore separator
api_key = "0001"        # Explicit string
created = 2024-01-15    # Native date type (TOML has date/datetime built in)
norway = "NO"           # String — no auto-coercion to boolean

TOML in Real Config Files

# Cargo.toml (Rust package manifest)
[package]
name = "my-service"
version = "0.1.0"
edition = "2021"

[dependencies]
tokio = { version = "1", features = ["full"] }
serde = { version = "1.0", features = ["derive"] }
serde_json = "1.0"

[profile.release]
opt-level = 3
lto = true

# pyproject.toml (Python project)
[project]
name = "my-api"
version = "1.0.0"
requires-python = ">=3.11"
dependencies = [
    "fastapi>=0.110",
    "pydantic>=2.0",
]

[tool.ruff]
line-length = 88
select = ["E", "F", "I"]

[tool.pytest.ini_options]
testpaths = ["tests"]
asyncio_mode = "auto"

YAML Anchors Have No TOML Equivalent

YAML anchors (&, *, <<:) allow value reuse within a file. TOML has no equivalent by design — repetition is intentional. The workaround for TOML is moving shared values to a [defaults] section and reading them in code:

# YAML with anchors
defaults: &defaults
  timeout: 30
  retries: 3

production:
  <<: *defaults
  host: "prod.example.com"

staging:
  <<: *defaults
  host: "staging.example.com"

# TOML equivalent — explicit repetition (or use [defaults] + code)
[defaults]
timeout = 30
retries = 3

[production]
host = "prod.example.com"
timeout = 30    # repeated explicitly
retries = 3

[staging]
host = "staging.example.com"
timeout = 30
retries = 3

Multiline Strings and Inline Tables

# TOML multiline strings (literal: no escapes; basic: with escapes)
description = """
This is a
multiline string.
"""

# Inline table (single line only — cannot span multiple lines)
server = { host = "localhost", port = 8080 }

# Array of tables (equivalent to YAML sequence of objects)
[[endpoints]]
path = "/api/users"
method = "GET"

[[endpoints]]
path = "/api/orders"
method = "POST"

Frequently Asked Questions

Does the conversion handle YAML boolean coercion (yes, on, no)? TypeMorph parses the YAML first, resolving all YAML type coercions (including the notorious yes/no/on/off booleans from YAML 1.1), then emits proper TOML booleans (true/false).

Can TOML handle all YAML structures? Almost. YAML supports heterogeneous sequences (arrays with mixed types) and anchors — neither exists in TOML. If your YAML uses these, you'll need to restructure the config after conversion.

When should I prefer YAML over TOML? YAML is better for deeply nested structures (Kubernetes manifests, GitHub Actions workflows) where TOML's section-header syntax becomes unwieldy. TOML is better for flat-to-moderately-nested config files (package manifests, tool configuration).

Is my YAML sent to a server? No. TypeMorph runs entirely in your browser — your config files, which may contain API keys or internal hostnames, never leave your machine.