JavaScript AST Viewer — Explore Code Structure
View a simplified Abstract Syntax Tree representation of JavaScript code.
How it works
- 1Paste or type your text in the input field
- 2Click "Process" — processing happens in your browser
- 3Copy the result or download as a text file
What to do next
About JavaScript AST Viewer
JavaScript AST Viewer performs javascript ast viewer as a focused single-page utility. View a simplified Abstract Syntax Tree representation of JavaScript code. Defaults are tuned for the common case so the first run is one click, with every option that matters exposed for the moments you need to fine-tune the result.
The right moment to reach for JavaScript AST Viewer is when you have a focused developer utility job that fits inside a browser tab. Open the page, drop in the file or paste your input, choose the options that matter, and the tool returns the result.
JavaScript AST Viewer is a static page plus a client-side engine. The browser does the work; there is no separate backend in the loop for the actual processing. That architecture is why the tool starts immediately, why it does not depend on the load on a remote service, and why running multiple jobs in a row does not slow it down.
Behind the controls you see, standard browser APIs is doing the actual developer utility. Formats are detected on load and the engine produces a deterministic output for any given input + options combination — useful when you need to re-run a job and expect identical results.
On limits: 0 MB per file is the ceiling. Output formats and quality settings are listed in the controls panel above, and they apply to every run.
Anyone who works with developer utility on a casual basis — data analysts wrangling JSON, engineers debugging API payloads, devops engineers crafting one-liners — finds JavaScript AST Viewer a quick way to get the result. The page loads in under a second, the controls are visible from a single screen, and the result downloads or copies in one click.
JavaScript AST Viewer returns the result as a download. If you are running multiple jobs, the output names will not collide as long as the input names differ. You can re-run with different settings as many times as you like; each run produces a fresh file with no caching trickery in between.
JavaScript AST Viewer is intentionally narrow in what it does, which makes it easy to slot into a longer workflow. Take its output, hand it to whichever next tool fits the job, and JavaScript AST Viewer stays out of your way until the next time you need it.
The transformation in JavaScript AST Viewer is deterministic — the same input plus the same options produces the same result every run. That predictability matters when the result has to match an upstream specification or be reproducible later.
Some background on the design choices behind JavaScript AST Viewer: every option you see on the page is there because a real workflow needs it, and every option that is not shown has been deliberately omitted to keep the common case fast. The bias is toward minimal-but-complete.
JavaScript AST Viewer produces deterministic output: the same input plus the same options always produces the same result. That predictability matters when the result has to match an upstream specification or be reproducible later.
Useful patterns when working with JavaScript AST Viewer: keep the input file open in another tab so you can compare against the result; give the output file a descriptive name when saving so you can find it later (the default name is sensible but generic); and treat each run as independent — the tool has no concept of "history", which means you cannot accidentally pollute one job with leftovers from another.
Common gotchas worth flagging: the supported formats are listed in the upload area. The 0 MB ceiling is per-file, not per-session; you can run as many separate jobs as you like, but a single oversized input will be rejected on load.
JavaScript AST Viewer is intentionally narrow in scope so the common case is fast and the result is predictable. If you ever need a variation it does not cover, browse the rest of the catalog — there is a good chance an adjacent tool already exists, and switching between tools is just a matter of opening another tab.
How it works
- 1Open the JavaScript AST Viewer workspace above. The interface is a single page, so there is nothing to navigate.
- 2Drop a developer file onto the upload area, or click to pick one from your device.
- 3Tweak the controls if the defaults are not quite right for your input. The options are kept short and labelled in plain language.
- 4Click to start the job. The engine (standard browser APIs) processes the input in the page; you can watch the progress indicator until it completes.
- 5Grab the output as soon as the run completes. You can also copy the result instead of downloading if the next tool in your workflow accepts pasted input.
- 6Run additional jobs as needed. The same controls and defaults apply on every run.
Common use cases
- Format a noisy log line into something a teammate can read using JavaScript AST Viewer.
- Inspect a payload during local development without writing a script.
- Decode a token to confirm its claims during a debugging session.
- Inspect a regex against a test string before committing it.
- Encode binary content for transport in a JSON body.
- Convert between data formats while wiring up an integration.
- Generate boilerplate from a single specification line.
- Generate a quick fixture without leaving the browser.
- Hash a string for a quick reproducibility check.
FAQ
Is this a full AST parser?
No — it provides a simplified, educational AST-like view showing major code structures.
What node types are shown?
Functions, variables, classes, imports, exports, control flow, and expression statements.
Can I use this for code analysis?
For learning purposes. For production AST work, use parsers like Acorn, Babel, or ESTree.
Does it show the full tree?
It shows top-level and first-nesting-level nodes. Deeply nested expressions are summarized.
Is TypeScript supported?
Basic TypeScript is recognized but type-specific nodes are not shown.
Is data sent to a server?
No — processing happens in your browser.
Is JavaScript AST Viewer really free?
JavaScript AST Viewer is free to use. The processing runs in your browser, which keeps the per-user cost low enough that the tool can be offered openly. The download is the same file the engine produced — you can use it for as many runs as you need.
How accurate is JavaScript AST Viewer?
JavaScript AST Viewer is built on standard browser APIs, which is the same class of engine used by professional developer utility pipelines. For deterministic operations, the output is byte-identical to what an equivalent CLI run would produce; for operations involving a codec or a model, the result is well within the range of what comparable tools generate. If you have a specific reference output you need to match, run a small test job first to confirm the configuration produces what you expect.
Will JavaScript AST Viewer keep working in a year?
JavaScript AST Viewer is updated whenever the underlying engine releases an improvement or a bug fix. Because the tool is delivered as a static page, every visit fetches the latest version automatically — there is no "version" to manage on your end. If a particular release ever changes default behaviour, the change is documented on Favtoo's changelog so you can confirm what shifted.
Can JavaScript AST Viewer run inside a corporate firewall?
JavaScript AST Viewer is a static page running an open-source engine in your browser, so a typical corporate firewall does not get in the way as long as it allows JavaScript to load from Favtoo. For teams that need to host it themselves on an internal network, the underlying engine (standard browser APIs) is open-source and can be packaged into a private build with the same behaviour. Reach out via the Contact page if that is something you are exploring.
Is there a programmatic version of JavaScript AST Viewer?
JavaScript AST Viewer is a browser-only tool by design and does not expose a hosted API. The reason is the same as the privacy story: there is no Favtoo backend doing the work, so there is no service to call. If you need to script the same transformation, the underlying engine (standard browser APIs) is open-source and can be used directly from your own code.
Does JavaScript AST Viewer ask for any browser permissions?
JavaScript AST Viewer only needs the standard web platform — file picker access for the inputs you choose to load, and optionally clipboard access if you copy the result rather than downloading it. There is no microphone, camera, geolocation or background-permission request, because none of those are needed for the work the tool does.
Is JavaScript AST Viewer keyboard accessible?
JavaScript AST Viewer uses native HTML controls wherever possible, which means keyboard navigation, focus rings, and screen-reader labels work the way the platform expects. The drop zone accepts files via the keyboard-accessible file picker as well as drag-and-drop, and result downloads use standard browser download flows. If you spot an accessibility gap, Favtoo treats it as a bug worth fixing.
Is JavaScript AST Viewer lossless?
JavaScript AST Viewer is built to preserve quality wherever the underlying developer format allows it. Operations that are mathematically lossless (e.g. structural transformations, lossless re-encoding) round-trip with no perceptible change. Operations that involve a lossy codec inevitably introduce small artefacts at the byte level, but the defaults aim at the sweet spot where output looks or sounds the same to a normal viewer or listener while still being meaningfully smaller or faster than the input.
Does JavaScript AST Viewer require a browser extension or plug-in?
No installation is needed. JavaScript AST Viewer runs as a normal web page, with no browser extension, no native helper, and no separate desktop client to download. That is partly a privacy choice — extensions can request broad permissions, while a regular page is sandboxed by default — and partly a convenience one: you can use JavaScript AST Viewer on any computer you have temporary access to without leaving anything installed on it.