5 Free Browser-Based Dev Tools: GraphQL Formatter, Docker Compose Validator, Dockerfile Linter, and More

I just shipped 5 new tools to DevNestio - a hub of 172 free, browser-only developer utilities. All tools are zero-signup, zero-upload, and work offline.

GraphQL Query Formatter & Minifier

https://devnestio.pages.dev/graphql-formatter/

Paste any GraphQL operation and get:

• Pretty-print - consistent indentation
• Minify - strips comments and whitespace for smaller request payloads
• Validation - brace/parenthesis balance check
• Operation detection - lists all named query, mutation, subscription, fragment

Useful for quick query cleanup before pasting into code reviews or API docs.

Protobuf (.proto) Formatter & Validator

https://devnestio.pages.dev/protobuf-formatter/

Online formatter and validator for Protocol Buffer .proto files:

• Duplicate field number detection
• Message and enum structure validation
• Syntax-highlighted output
• One-click copy

Great for a sanity check before pushing .proto changes in a gRPC service.

Docker Compose Validator

https://devnestio.pages.dev/docker-compose-validator/

Paste your docker-compose.yml to catch:

• Missing services section
• Services without image or build
• Invalid port mappings (80:80, 127.0.0.1:8080:80, 53:53/udp, ranges…)
• depends_on referencing non-existent services
• Circular dependency detection (A→B→A)
• Unknown restart policies

# This will flag errors:
services:
  web:
    ports:
      - "abc:xyz" # invalid port
    depends_on:
      - missing_service # unknown service

Dockerfile Analyzer & Linter

https://devnestio.pages.dev/dockerfile-analyzer/

Analyzes your Dockerfile for best practice violations across three categories:

Security

• sudo usage inside RUN
• Container running as root (no USER instruction)
• Secrets baked into ENV / ARG (password, secret, token, key)

Image size

• :latest base image tag
• apt-get update in a separate RUN (stale cache risk)
• apt-get install without --no-install-recommends
• apt cache not cleaned (rm -rf /var/lib/apt/lists/*)
• ADD used for local files instead of COPY

Layer optimization

• Consecutive RUN instructions (suggest chaining with &&)
• High total layer count

Also flags the absence of WORKDIR and celebrates multi-stage builds and HEALTHCHECK when present.

Email Header Analyzer

https://devnestio.pages.dev/email-header-analyzer/

Paste raw email headers and instantly get:

Authentication Results

• SPF ✅ pass
• DKIM ✅ pass
• DMARC ✅ pass

Phishing investigation often starts here - a failed SPF or DKIM check is a red flag.

Phishing Signals

• Reply-To domain ≠ From domain - classic impersonation trick
• Return-Path domain mismatch
• Spam score / X-Spam-Flag detection

Routing Trace
Parses all Received: headers to show each hop the email traveled through, including originating IP addresses.

Three Tabs

• Summary - From/To/Subject/Date/Message-ID + auth status
• Routing - hop-by-hop trace with IP addresses
• All Headers - raw dump of every header field

Handy when your security team needs to quickly triage a suspicious email without spinning up a full mail analysis tool.

Implementation Notes

All five tools follow the same constraints:

• Vanilla JS, single HTML file - no bundler, no framework, works offline
• 80+ Node.js assert tests - core logic is extracted and tested independently of the browser
• No external YAML/parsing libraries - the Docker Compose validator uses a custom line-by-line indent parser

DevNestio now has 172 tools in total. If there's a utility you'd find useful, drop a comment - I'm always looking for the next one to build.