Spoold is a free, privacy-first developer toolbox. Paste into the Magic Box and it detects JSON, HTML, JWT, curl, OpenAPI, CSV, timestamps, and more—then suggests the best tool. You can also browse the full catalog by category. No sign-up is required.

Is Spoold free to use?

Yes. Core tools are free. Heavy work runs in your browser so your payloads are not processed on Spoold servers for formatting, decoding, and similar utilities.

Is my data safe with Spoold?

Tool processing for supported client-side utilities happens in your browser. Encrypted share links are designed so only people with the link can read the payload. Review the Privacy Policy for details on cookies, optional ads, and third-party services.

What tools are available?

Spoold ships 61+ tools including JSON formatter and diff, JSON Schema validation, YAML and TOML converters, HTML and Markdown preview, JWT decode and sign, OpenAPI/Swagger viewer with curl, GraphQL formatter, curl to code and curl compare, certificate viewer, CSV preview, regex tester, Mermaid, code editor, LLM token utilities, QR codes, and many encoding and text utilities.

Does Spoold show ads?

The site may display advertisements or sponsored placements to help keep the service free. House promotions highlight other Spoold tools. Ads do not change the fact that supported tools process your pasted content locally in the browser. You can read how to manage ad cookies and opt-outs in the Privacy Policy.

Can I use keyboard shortcuts?

Yes. Press Cmd or Ctrl+K to open tool search, use / from the homepage, and use per-tool shortcuts (shown in the UI) such as jj for JSON and hh for HTML where configured.

Markdown Preview & Editor

Guide: Markdown preview & editor

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What is this tool?

Spoold's Markdown preview is a browser-based editor and live renderer for .md files. The left side uses a Monaco editor (syntax highlighting, folding, line numbers); the right side shows HTML output produced by marked with GitHub Flavored Markdown (GFM) and line breaks enabled so single newlines behave closer to GitHub comments than strict CommonMark.

Switch between split, source-only, and preview-only layouts; drag the divider to change how much space Markdown vs preview uses. On the Preview card, Copy HTML puts the rendered fragment on the clipboard; the adjacent HTML action downloads a minimal standalone .html document (embedded styles for prose, code blocks, and tables). Save, share, and history follow the same Spoold document model as other tools—nothing is uploaded for parsing alone.

Why use it

READMEs, ADRs, changelogs, and support macros are almost always Markdown. Pasting into this page is faster than pushing to a branch just to see tables, task lists, and fenced code render—especially when you are tuning alignment, anchor text, or relative image paths before opening a PR.

Spot broken list nesting, heading levels, and link targets before they hit review.
Compare how GFM treats strikethrough, autolinks, and pipe tables vs your static site generator (treat Spoold as one signal, not the only truth).
Hand off a downloaded HTML snapshot to someone who does not use Markdown—use only for trusted content.

Stack & privacy

marked runs after a dynamic import so the bundle stays lean until you open the tool. Parsing and DOM updates happen on your machine; network calls only occur for normal browser behavior (for example loading remote images if your Markdown references https:// URLs). Share links and saved documents use Spoold's document pipeline when you explicitly choose those actions.

Key features

Monaco Markdown — Folding, word wrap, line numbers, theme synced with app light/dark.
GFM-oriented output — Tables, task lists, strikethrough, autolinks; code blocks styled in the preview pane.
Resizable split — Drag the vertical gutter between editor and preview (split mode).
Next tool suggestions — When HTML output exists, jump to related Spoold tools from the header strip.
Guide link — Quick scroll to this reference from the tool chrome.

Preview & HTML export

Copy HTML copies the rendered inner HTML (what you see in the preview body), useful for CMS HTML fields or email clients that accept rich fragments—still run through your own sanitizer if the destination is multi-tenant.

Download HTML wraps the same body in a complete document with a small default stylesheet (readable max width, code and table borders). It is meant for quick archives or demos, not as a full design system. For arbitrary HTML/CSS/JS sandboxes, use HTML preview.

Use cases

Scenario	How this tool helps
README polish	Preview badges, tables, and code fences before commit.
Support macros	Paste canned Markdown replies and confirm lists and links render.
Docs handoff	Download HTML for stakeholders who want a file, not a repo.
Learning GFM	Toggle split view to associate source syntax with output side by side.

How to use

Open split mode (default): edit Markdown on the left; preview updates as marked parses your text.
Use Source or Preview only when you need full-width writing or reading.
Drag the narrow divider between panes to allocate more space to the editor or preview.
In the Preview card header, copy HTML or download the standalone file after you are happy with the render.
Use Save / Share / History when you want a named copy or a link—same patterns as other Spoold editors.

GFM & limits

Output follows marked with GFM-ish options, not a pixel-perfect clone of GitHub's entire pipeline (security sanitization, emoji shortcodes, custom plugins, and math differ). If something renders here but not on your site, compare your SSG's Markdown flavor and plugins.

Raw HTML inside Markdown is passed through to the DOM—only paste content you trust. For untrusted user Markdown, always sanitize server-side before storage or use a strict subset. Mermaid and LaTeX math are not first-class here; use the Mermaid tool for diagrams.

Best practices

Keep one blank line between block elements when debugging odd spacing—GFM + breaks can surprise you if you rely on implicit joins.
Use fenced code blocks with a language tag (```ts) for clearer highlighting in preview and on GitHub.
Prefer relative links for repo assets; verify they resolve in your real host path, not only in this tool's origin.
Treat downloaded HTML as untrusted when re-hosting—strip scripts and inline event handlers if you did not author the Markdown.

FAQ

Is my Markdown uploaded?

Parsing runs locally in your browser. Save and share send data only when you use those features.

What is the difference between Copy HTML and download?

Copy HTML grabs the rendered fragment for pasting elsewhere. Download wraps that body in a full HTML document with basic styles so you can open or archive a single file.

Does it support Mermaid or math?

Not in this tool—use the dedicated Mermaid page or a math-capable stack for KaTeX/MathJax.

Why do line breaks behave like GitHub issues?

marked is configured with breaks enabled so single newlines create <br> in prose—closer to many GFM contexts than strict CommonMark.

Will remote images load in preview?

If your Markdown uses absolute https image URLs, the browser will fetch them like any other page. Broken or CORS-blocked images show as the browser decides.

Core: markdown preview online, live markdown editor, GFM preview, GitHub flavored markdown viewer, readme md preview, md to html browser, markdown split view editor, monaco markdown preview.

Output: copy rendered markdown html, export markdown to html file, download github readme as html, markdown table preview online, fenced code block preview, gfm task list preview.

Workflow: technical documentation markdown, changelog md preview, wiki markdown draft, slack discord markdown test (approximate), static site markdown check before hugo jekyll.

Compare: commonmark vs gfm line breaks, markdown vs rich text editor, notion markdown export preview (awareness).

Safety: sanitize markdown html xss (reminder for production), trusted vs untrusted markdown.

Similar tools

Conclusion

Spoold's Markdown preview pairs a real editor with GFM-oriented HTML, a resizable split, and practical HTML copy or download from the Preview toolbar—ideal for tightening docs before they ship. Layer HTML preview, HTML entities, and Mermaid when your content pipeline mixes formats.