Free Grammar Checker for Markdown: ProseLint Web vs. Commercial Tools

Every technical writer, content creator, and developer working with markdown has faced this dilemma: pay for a commercial grammar checker with features you don't need, compromise your privacy by uploading sensitive content to the cloud, or settle for basic spell-check tools that miss style inconsistencies.

There's a better way. ProseLint Web brings professional-grade grammar and style checking to markdown files, completely free, with zero privacy compromises. Unlike commercial tools designed for general writing, ProseLint Web is purpose-built for technical content, documentation, and markdown-based workflows.

The commercial grammar checker problem

Tools like Grammarly, ProWritingAid, and Microsoft Editor dominate the writing quality space. They're powerful, but they come with significant drawbacks for technical writers and developers:

Subscription costs add up fast: Grammarly Premium costs $144/year. ProWritingAid charges $120/year. For teams, multiply that by every writer. Many organizations can't justify these costs for documentation work.

Privacy concerns are real: Commercial grammar checkers upload your content to their servers for processing. When you're working with unreleased features, proprietary API documentation, or confidential content, sending text to third-party servers violates security policies. Even personal drafts deserve privacy.

Generic writing rules miss the mark: Commercial tools are optimized for blog posts, essays, and business writing. They flag technical terminology as errors, suggest rewrites that lose precision, and don't understand documentation patterns like API references, code snippets, or command-line examples.

Markdown support is an afterthought: Most commercial checkers struggle with markdown syntax. They treat code blocks as prose, flag intentional formatting as errors, and can't distinguish between content that needs checking and markup that should be ignored.

Why technical content needs specialized linting

Technical writing has different quality standards than general content. Documentation, markdown files, READMEs, and technical blog posts require:

Consistency across terminology: Product names, API terms, and technical concepts must be capitalized and referenced identically throughout
Style guide adherence: Professional organizations (Microsoft, Google, Red Hat) publish detailed writing guides that commercial tools don't enforce
Markdown-aware checking: Linters must parse markdown syntax correctly, ignoring code blocks, respecting link text vs. URLs, and understanding heading hierarchies
Format support beyond markdown: Documentation teams work with MDX, AsciiDoc, HTML, and plain text alongside markdown

Vale, the open-source prose linter created by Joseph Kato, was designed specifically for these needs. ProseLint Web brings that specialized linting to your browser—free, private, and purpose-built for technical content.

How ProseLint Web compares to commercial tools

Let's break down the comparison across the dimensions that matter most for technical writing:

Price and access

Commercial checkers: Grammarly Premium ($144/year), ProWritingAid ($120/year), and similar tools require paid subscriptions for advanced features. Free tiers have strict limits and lack the style checking features technical writers need.

ProseLint Web: Completely free. No subscription, no usage limits, no feature gates. The same professional rule packages used by major tech companies are available to everyone at no cost.

Privacy and data handling

Commercial checkers: Upload your content to remote servers for processing. Even with privacy policies, your drafts, unreleased documentation, and confidential content pass through third-party infrastructure.

ProseLint Web: Runs entirely in your browser using WebAssembly. Your content never leaves your device. No server contact, no data transmission, no cloud processing. Works offline after rule packages are downloaded. Privacy is guaranteed by architecture, not just policy.

Technical content understanding

Commercial checkers: Generic writing rules designed for essays and business content. Flag technical terms as errors, suggest inappropriate rewrites, and struggle with documentation patterns.

ProseLint Web: Built on Vale's professional rule packages from organizations like Microsoft, Google, Red Hat, GitLab, and Elastic. These packages understand technical writing patterns, respect industry terminology, and enforce proven documentation standards.

Markdown and format support

Commercial checkers: Basic markdown support at best. Often flag code blocks, fail to parse complex documents, and treat markdown syntax as prose errors.

ProseLint Web: Native support for markdown, MDX, AsciiDoc, HTML, and plain text. Purpose-built for docs-as-code workflows and technical content creation.

Integration with existing workflows

Commercial checkers: Browser extensions, web editors, and desktop apps. Separate from your existing tooling, requiring copy-paste workflows or switching between applications.

ProseLint Web: Works alongside the Vale CLI for CI/CD enforcement. Use the browser tool for quick checks during authoring, then rely on the same Vale engine in your CI pipeline for enforcement. Seamless integration with docs-as-code practices.

Customization and control

Commercial checkers: Limited rule customization. You can disable some suggestions, but you can't define custom terminology, create organization-specific rules, or build your own style guide.

ProseLint Web: Full access to Vale's extensible rule system. Start with professional packages, then customize rules, add organization-specific terminology, and create custom checks for your unique style requirements. Advanced users can write custom rules using Vale's YAML-based syntax.

Who should use ProseLint Web instead of commercial tools

ProseLint Web is ideal for:

Technical writers and documentation engineers: If you're writing API docs, developer guides, or technical tutorials, Vale's professional style guides understand your content better than generic checkers.

Open-source contributors: No budget for commercial subscriptions? ProseLint Web gives you professional-grade linting without cost barriers.

Privacy-conscious organizations: Companies with strict security policies about cloud services can use ProseLint Web without compromising on writing quality.

Development teams: Developers writing READMEs, documentation, or markdown content in repos can lint before committing without installing local tools or paying for individual subscriptions.

Content teams working with multiple formats: If you're publishing content in markdown, MDX, AsciiDoc, HTML, and plain text, ProseLint Web's format support exceeds commercial offerings.

Teams already using Vale CLI: If you're enforcing Vale in CI/CD, the browser tool gives writers the same linting experience locally without requiring CLI installation or configuration.

When commercial tools might still make sense

Be honest about use cases where commercial tools excel:

General business writing: If you're primarily writing emails, blog posts for non-technical audiences, or business documents, Grammarly and ProWritingAid are optimized for these formats.

Advanced grammar explanation: Commercial tools often provide detailed grammar lessons and explanations designed for learning. Vale focuses on style guide enforcement rather than grammar education.

Non-technical content teams: If your team doesn't work with markdown, doesn't follow technical style guides, and needs features like plagiarism checking or tone analysis, commercial tools may fit better.

Getting started with ProseLint Web for free

Making the switch from commercial tools is straightforward:

For individual writers

Visit the ProseLint Web editor and bookmark it in your writing toolkit
Select a professional rule package that matches your needs:
- Microsoft Writing Style Guide for general technical content
- Google Developer Documentation Style Guide for developer-focused docs
- Red Hat Documentation Style Guide for enterprise technical writing
- Or explore other packages from GitLab, Elastic, and community contributors
Paste your markdown content or upload files directly into the browser editor
Review suggestions with clear explanations and one-click fixes
Copy corrected content back to your local files or apply fixes manually

For documentation teams

Standardize on a rule package that matches your organization's voice
Add Vale CLI to your CI/CD pipeline to enforce style on pull requests
Link the browser tool in CONTRIBUTING.md for contributors who won't install local tooling
Document your style standards so writers know which package to use
Train team members on the browser tool for self-review before submitting PRs

For developers and engineers

Use the browser tool before committing documentation changes to repos
Lint README files to maintain consistency across project documentation
Check inline code comments in markdown format before publishing
Integrate with docs-as-code workflows where Vale CLI runs in CI

Real-world impact: case studies

Open-source project maintainer: "We couldn't afford Grammarly subscriptions for all contributors. ProseLint Web lets anyone contributing docs run the same Microsoft style guide we enforce in CI—completely free. Documentation quality improved immediately."

Technical writing team at SaaS company: "Our security policy prohibited uploading unreleased feature docs to third-party services. ProseLint Web solved that. Writers get instant feedback without sending content off-device. Privacy compliance is built-in."

Solo developer: "I was paying $144/year for Grammarly but barely using it. ProseLint Web gives me better markdown support and technical writing rules at zero cost. Canceled my subscription and haven't looked back."

Frequently asked questions

Is ProseLint Web really completely free? Yes. No subscriptions, no usage limits, no feature gates. All professional rule packages are free to use.

How does browser-based linting work? Vale is compiled to WebAssembly and runs directly in your browser. No server contact required. Your content stays local.

Can I use my own custom Vale rules? Advanced customization requires Vale CLI configuration. The browser tool supports selecting from available professional packages and adjusting rule severity levels.

Does this replace Vale CLI? No, it complements it. Use the browser tool for quick checks during authoring. Use Vale CLI in CI/CD for enforcement and automation.

What if I'm already paying for Grammarly? Try ProseLint Web with your technical content and compare results. You may find the specialized rules and markdown support justify switching, or you might use both for different content types.

Conclusion: professional writing quality shouldn't require compromise

You shouldn't have to choose between quality writing tools and your budget. You shouldn't have to compromise privacy to get professional style checking. And you shouldn't settle for generic grammar rules when your content deserves specialized technical linting.

ProseLint Web delivers professional-grade writing quality for markdown and technical content—completely free, with zero privacy compromises. Try it with your next documentation project and experience the difference purpose-built tooling makes.

Resources

ProseLint Web editor — free, privacy-first grammar and style checking for markdown
Vale CLI and documentation — the open-source prose linter for CI/CD integration
Vale packages repository — professional style guides from Microsoft, Google, Red Hat, and more
Microsoft Writing Style Guide — authoritative reference for technical content
Google Developer Documentation Style Guide — standards for developer-focused documentation