Merge YAML Files Online - Free YAML Merger Tool
This tool combines multiple YAML files into one. Used by DevOps engineers and developers working with Kubernetes configs, Docker Compose files, GitHub Actions workflows, and Ansible playbooks. Runs entirely in your browser, free.
Drop YAML files or click to browse
Merge multiple YAML files
Need sample YAML files for testing?
Before & After
YAML merge in action
# config-dev.yaml
environment: development
database:
host: localhost
port: 5432
# config-prod.yaml
environment: production
database:
host: prod-db.example.com
port: 5432merged:
# From config-dev.yaml
- |
environment: development
database:
host: localhost
port: 5432
# From config-prod.yaml
- |
environment: production
database:
host: prod-db.example.com
port: 5432How It Works
Four simple steps
Upload YAML Files
Drop multiple .yaml or .yml files directly into the merger interface.
Choose Strategy
Select array, object, or document separation based on your needs.
Merge Configs
Combine files while maintaining indentation and structure.
Download Result
Get merged YAML file ready for deployment or configuration.
Programmatic Merge
Python & Bash
import yaml
def merge_yaml_files(files, strategy="array", root_key="merged"):
merged_data = []
for filepath in files:
with open(filepath, 'r') as f:
data = yaml.safe_load(f)
merged_data.append(data)
if strategy == "array":
output = {root_key: merged_data}
elif strategy == "object":
output = {root_key: {}}
for i, filepath in enumerate(files):
key = filepath.replace('.yaml', '').replace('.yml', '')
output[root_key][key] = merged_data[i]
else: # document
output = merged_data
with open("merged.yaml", 'w') as f:
if strategy == "document":
yaml.dump_all(output, f, default_flow_style=False)
else:
yaml.dump(output, f, default_flow_style=False)
print(f"Merged {len(files)} YAML files")
files = ["config-dev.yaml", "config-prod.yaml"]
merge_yaml_files(files, strategy="object", root_key="environments")#!/bin/bash
# Merge YAML files with document separators
OUTPUT="merged.yaml"
# Clear output file
> "$OUTPUT"
# Merge all YAML files
for file in configs/*.yaml; do
if [ -f "$file" ]; then
echo "# From $file" >> "$OUTPUT"
cat "$file" >> "$OUTPUT"
echo "---" >> "$OUTPUT"
fi
done
# Remove trailing separator
sed -i '$ d' "$OUTPUT"
echo "Merged YAML files into $OUTPUT"Use Cases
Real-world scenarios
Environment Configs
Combine base configuration with environment-specific overrides for dev, staging, and production deployments.
Kubernetes Manifests
Consolidate multiple resource definitions into single files for easier kubectl apply and atomic deployments.
CI/CD Pipelines
Merge pipeline configuration fragments for different stages, environments, or teams into complete workflows.
Docker Compose
Combine service definitions from multiple compose files into comprehensive stack configurations.
FAQ
Common questions
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Complete Guide
In-depth walkthrough
Deep merge vs shallow merge for YAML — which you need
Shallow merge: top-level keys from all files are combined. If two files have the same top-level key, the last file's value wins and overwrites the first. Example: file1 has database: postgres and file2 has database: mysql. Shallow merge gives you database: mysql.
Deep merge: nested keys are merged recursively. If both files have a services key with different sub-keys, deep merge combines them instead of overwriting. Example: file1 has services: {web: nginx} and file2 has services: {db: postgres}. Deep merge gives you services: {web: nginx, db: postgres}.
Use deep merge for Kubernetes and Docker Compose files that share keys like services, volumes, or env. Use shallow merge for simple config files where you want later values to override earlier ones, like environment-specific database URLs or API keys.
Before shallow merge: file1 port: 3000, file2 port: 8080. After: port: 8080. Before deep merge: file1 config: {timeout: 30}, file2 config: {retries: 3}. After: config: {timeout: 30, retries: 3}.
Most YAML merge tools default to shallow merge because it is simpler and more predictable. If you need deep merge behavior, look for tools that explicitly support recursive merging or use a library like yq with the merge operator.
Merging Kubernetes, Docker Compose, and GitHub Actions files
Kubernetes: merging base config with environment-specific overlays is common for multi-environment deployments. Use deep merge to combine resource limits, environment variables, and volume mounts. Watch for conflicting resource limits (memory, CPU) where the last value wins. Validate with kubectl apply --dry-run after merging.
Docker Compose: merging a base docker-compose.yml with a docker-compose.override.yml is standard practice. Docker does this natively with the -f flag (docker-compose -f base.yml -f override.yml up), but the tool works for pre-merge preview or creating a single file for deployment.
GitHub Actions: combining reusable workflow fragments lets you build complex workflows from smaller pieces. YAML anchors and aliases may need manual cleanup after merging because they do not work across separate files. Convert anchors to explicit values or use GitHub's reusable workflows feature instead.
Ansible: merging variable files from different environments (dev, staging, prod) creates a single vars file for playbook execution. Use shallow merge when environment-specific values should override base values. Use deep merge when combining role defaults with environment-specific overrides.
For all these workflows, test the merged output with the target tool before deploying. Run kubectl apply --dry-run, docker-compose config, or ansible-playbook --syntax-check to catch merge errors early.
YAML syntax issues that cause merge failures
Indentation errors are the most common problem. YAML uses spaces, not tabs. Tabs will break the parser with cryptic errors like "mapping values are not allowed here". Set your editor to convert tabs to spaces and use consistent indentation (2 or 4 spaces, not mixed).
Duplicate keys in the same file are not allowed in strict YAML. If you have two name: keys at the same level, the parser will reject it or silently use the last value. Check for duplicates before merging. Some parsers allow duplicates but this is non-standard behavior.
Special characters in values need quoting. Colons, brackets, braces, and leading/trailing spaces require quotes. Example: url: http://example.com needs to be url: "http://example.com" because the colon after http confuses the parser. Use quotes for any value containing special characters.
Validate YAML before merging: paste into yamllint.com or use the VS Code YAML extension (Red Hat's YAML extension). Both catch syntax errors, indentation problems, and duplicate keys. Fix all validation errors before attempting to merge files.