Skip to content

Guide

Convert YAML to JSON in code

When the conversion belongs in a script or a build step rather than a browser tab, these are the equivalents.

By yamltojsonfree · Published · Updated

Python, Node.js, Go, and the command line

Each snippet reads input.yaml and prints formatted JSON. They aren’t interchangeable, though — the note under each one tells you which YAML version that library implements, and that difference can silently change your data.

Python

import json, yaml

with open("input.yaml") as f:
    data = yaml.safe_load(f)          # safe_load, never load()

print(json.dumps(data, indent=2))

PyYAML implements YAML 1.1, so `no` becomes False here — unlike the browser tool, which defaults to 1.2.

Node.js

import { readFileSync } from "node:fs";
import { load } from "js-yaml";

const data = load(readFileSync("input.yaml", "utf8"));
console.log(JSON.stringify(data, null, 2));

js-yaml v5 defaults to YAML 1.2 — the same engine and defaults the browser tool on this site uses.

Go

import (
    "encoding/json"
    "os"
    "sigs.k8s.io/yaml"
)

in, _ := os.ReadFile("input.yaml")
out, _ := yaml.YAMLToJSON(in)
os.Stdout.Write(out)

sigs.k8s.io/yaml converts through JSON tags, which is what Kubernetes itself uses.

Bash (yq)

# Single document
yq -o=json input.yaml

# Multi-document into a JSON array
yq -o=json -I=2 'select(document_index >= 0)' -N input.yaml

# Minified
yq -o=json -I=0 input.yaml

This is mikefarah/yq. The other yq (kislyuk) is a jq wrapper with different flags.

Three things to get right in a script

Use the safe loader. In Python, yaml.load() without an explicit loader can construct arbitrary Python objects from tagged YAML — which is code execution if the input isn’t yours. safe_load() parses plain data only, and there is almost never a reason to use anything else.

Know your YAML version. PyYAML reads YAML 1.1, so country: NO comes out as False; js-yaml v5 and Go’s Kubernetes-flavored parser read 1.2, so the same line stays a string. A pipeline that converts with one library and validates with another can disagree with itself. The full list of affected values is in the YAML 1.1 vs 1.2 guide.

Handle multi-document streams. Kubernetes and Helm output is usually several documents separated by ---. A plain load reads only the first one and silently drops the rest — use yaml.safe_load_all() in Python, loadAll() in js-yaml, or the yq invocation shown above to get every document.

Or skip the script entirely

For a one-off conversion, the free YAML to JSON converter does everything above in the browser: multi-document streams, anchors and merge keys, YAML 1.1 and 1.2 modes, and errors pinned to the exact line. Nothing is uploaded — the parser runs entirely on your machine.

References

Keep reading

YAML 1.1 vs 1.2

Why country: NO becomes false in one version and stays a string in the other — the Norway problem, and every value that changes meaning.

Read the guide

Common YAML errors

The six errors behind almost every failed parse — what each one means, why the parser complains, and the exact fix.

Read the guide

YAML to JSON

Convert YAML into formatted or minified JSON, with errors pinned to the exact line.

Open

JSON to YAML

Turn JSON back into readable YAML, with control over indentation and key order.

Open

YAML Validator

Check YAML for syntax errors and get a plain-English explanation of what went wrong.

Open

YAML Formatter

Reformat messy YAML with consistent indentation and keep your comments intact.

Open