Devcontainer Validator

Validate devcontainer.json files for syntax, structure, features, ports, lifecycle scripts, customizations, and security best practices in VS Code Dev Contai...

Validate devcontainer.json files for VS Code Dev Containers, GitHub Codespaces, and DevPod.

What it does

Checks your devcontainer.json (JSONC — comments and trailing commas supported) for common mistakes across six areas:

• Structure — required fields, conflicts between image/dockerFile/dockerComposeFile, unknown keys
• Features — OCI reference format, duplicates, empty options
• Ports & networking — forwardPorts format, port ranges, portsAttributes consistency
• Lifecycle scripts — command types, empty commands, shell injection patterns
• Customizations — VS Code extensions format, settings type, extension ID validation
• Best practices — remoteUser, privileged mode, workspaceFolder, dangerous capabilities

Rules (24+)

Category	Rules	Examples
Structure (6)	Invalid JSONC syntax, missing image source, unknown top-level keys, empty name, image+dockerFile conflict, dockerFile+compose conflict	"image": "...", "dockerFile": "..." both set
Features (4)	Invalid features format, feature ID not valid OCI ref, empty feature options, duplicate features	"features": ["go"] (should be object)
Ports & networking (4)	forwardPorts not array, invalid port numbers, port out of range, portsAttributes referencing unlisted ports	"forwardPorts": [99999]
Lifecycle scripts (4)	Invalid command type, empty commands, shell injection patterns, onCreateCommand usage hints	"postCreateCommand": ""
Customizations (3)	extensions not array of strings, invalid extension ID format, settings not object	"extensions": [123]
Best practices (3+)	Missing remoteUser (root warning), privileged: true, missing workspaceFolder, dangerous capAdd entries	"capAdd": ["SYS_ADMIN"]

Output formats

• text — human-readable with severity tags ([E] [W] [I])
• json — structured with summary counts
• summary — one-line PASS/WARN/FAIL

Exit codes

• 0 — no errors (warnings/info allowed)
• 1 — errors found (or --strict with any issue)
• 2 — file not found or parse error

Commands

validate

Full validation of all rules.

bash

python3 scripts/devcontainer_validator.py validate devcontainer.json
python3 scripts/devcontainer_validator.py validate --format json .devcontainer/devcontainer.json
python3 scripts/devcontainer_validator.py validate --strict devcontainer.json

structure

Validate only structure rules (required fields, conflicts, unknown keys).

bash

python3 scripts/devcontainer_validator.py structure devcontainer.json

features

Validate only the features section.

bash

python3 scripts/devcontainer_validator.py features devcontainer.json

security

Validate only security-related rules (privileged, capAdd, shell injection, remoteUser).

bash

python3 scripts/devcontainer_validator.py security --strict devcontainer.json

Options

Option	Values	Default	Description
--format	text, json, summary	text	Output format
--min-severity	error, warning, info	info	Filter by minimum severity
--strict	flag	off	Exit 1 on any issue

Requirements

• Python 3.8+ (pure stdlib, no dependencies)

Examples

bash

# Quick check
python3 scripts/devcontainer_validator.py validate devcontainer.json

# CI pipeline
python3 scripts/devcontainer_validator.py validate --strict --format summary devcontainer.json

# Security audit only
python3 scripts/devcontainer_validator.py security --format json devcontainer.json

# Filter noise
python3 scripts/devcontainer_validator.py validate --min-severity warning devcontainer.json