What exactly is gron?

gron is a way of writing JSON as flat, greppable assignment statements, popularised by Tom Hudson's tomnomnom/gron CLI. Instead of nested braces, each leaf becomes one line like json.user.email = "a@b.com"; with the full path on the left. The whole point is that grep then works on JSON: you no longer need a jq filter to find where a value lives, you just pipe gron output into grep and read the matching paths.

How do I read the json.a.b = 1 format?

Each line is path = value;. The left side is the absolute path from the root variable (json by default) down to one value, using .key for object keys and [n] for array indices. The right side is a JSON literal: strings keep quotes (= "hi";), numbers, booleans and null are bare (= 42;, = true;, = null;). A line like json.users[0].name = "Ada"; means the first user's name is Ada.

How is this different from json-flatten?

json-flatten turns JSON into a flat object of dot-keys, like {"a.b": 1}. gron instead emits assignment statements with a specific syntax (json.a.b = 1;), keeps a declaration line for every container, and is built to round-trip through ungron back to the exact original. Flatten is for getting a flat map; gron is for grepping deep JSON on the command line and reconstructing it afterward.

ungron is the reverse direction: it reads gron lines such as json.arr[0] = 10; and rebuilds the original JSON. It walks each path, creating objects and arrays as needed, then places the JSON literal at that location. So the loop gron then edit then ungron lets you tweak a deep value with a text editor or sed and rebuild valid JSON, without ever opening a nested structure by hand.

How do I use grep to find a deep value?

Run the JSON through gron, then grep the lines. For example gron api.json | grep -i token shows every path whose name contains token, with its value, so json.auth.refresh_token = "…"; jumps out immediately. Add grep '\[3\]' to isolate the fourth array element, or grep -c to count matches. This tool gives you the same gron text in the browser, ready to copy into a grep pipeline.

Is my JSON sent anywhere?

No. Both gron and ungron run as plain JavaScript in your browser tab, so the JSON you paste and the output you copy never touch a server. The only thing that can leave the page is the shareable URL, which encodes your input in the link, so avoid sharing a URL that contains secrets and use the copy button instead for anything sensitive like tokens or private payloads.

Grep a deep value out of a giant API response

A 4000-line JSON payload comes back from an API and you need the auth token buried somewhere inside. Paste it, switch to JSON to gron, copy the lines, and run grep -i token over them. Instead of scrolling through nested braces you get json.data.session.refresh_token = "eyJ…"; on one line with its full path. Same trick finds every URL, every id, every email — grep the word, read the path, done.

Diff two JSON files line by line

Structured JSON diffs are noisy because formatting and key order move things around. Run both files through gron and the output is a flat, stable list of path = value lines, so an ordinary line diff (or git diff) shows exactly which leaves changed and where. A reordered object no longer looks like a hundred-line change; only the genuinely different assignments stand out.

Edit a buried value with sed, then rebuild

You need to bump json.config.replicas from 2 to 5 in a config you would rather not hand-edit through three levels of nesting. gron the file, change the one line (by hand or with sed), then ungron it back into valid, pretty-printed JSON. The path syntax makes the edit unambiguous and the round trip guarantees the structure is rebuilt correctly.

Teach or document a JSON shape

When you explain an API response in a doc or a code review, a wall of braces hides the structure. gron lines spell out every path explicitly, so a reader sees json.items[0].price = 9.99; and immediately knows the shape, the types and where each field lives — no mental parsing of indentation required.

gron Converter — JSON to gron and ungron

Make JSON greppable. json.users[0].name = "Ada"; one leaf per line, and ungron right back. Runs in your browser.

Runs locally
Category Developer & DevOps
Best for Formatting, validating, shrinking, or inspecting code-adjacent text.

Turn JSON into greppable gron lines (json.users[0].name = "Ada";), or ungron them back to JSON. Every leaf is one line, so you can pipe it through grep to find deep values. Strings keep quotes; numbers, booleans and null stay bare.

Direction

Root name

Input

✓ Converted

Output

json = {};
json.users = [];
json.users[0] = {};
json.users[0].name = "Ada";
json.users[0].admin = true;
json.count = 1;
json.next = null;

What this tool does

Convert JSON into gron and back, entirely in your browser. gron, the format from Tom Hudson's tomnomnom/gron tool, rewrites a JSON document as one assignment statement per line, like json.users[0].name = "Ada"; — an absolute path on the left, a JSON literal on the right. Because every deep value sits on its own line with its full path, you can pipe the output straight into grep to find where a value lives: gron data.json | grep name. Object keys join with dots, array elements use [index], and keys that are not plain identifiers are bracket-quoted as json["weird key"]. Strings keep their quotes, while numbers, booleans and null stay bare so the lines read like real assignments. The ungron direction reads those statements back and rebuilds the original JSON exactly, so the round trip is lossless. Pick the root variable name, paste, and copy. Nothing is uploaded; the JSON and the gron output never leave the page.

Tool details

Input: Files + Text + Numbers; The page exposes text boxes, numeric controls, file pickers, or structured inputs depending on the tool.
Output: Live result + Copy; The result area focuses on usable output, with copy, download, or preview actions when supported.
Privacy: Browser-side processing; The main tool logic does not call an external API, so inputs normally stay in the current tab.
Save / share: Shareable URL state; Key settings are encoded in the URL so another person can reopen the same setup.
Performance budget: Initial JS <= 9 KB; No WASM budget is declared, keeping the tool quick to open on mobile.
Best fit: Developer & DevOps · Developer; Category and role tags drive related tools, internal links, and quick fit checks.

How to use

1. Input

Paste or drop your content into the tool panel.
2. Process

Click the button. All processing is local in your browser.
3. Copy / Download

Copy the result or download to disk in one click.

How gron Converter (JSON to gron / ungron) fits into your work

Use it in the small gaps between coding, reviewing, debugging, and shipping.

Developer jobs

Formatting, validating, shrinking, or inspecting code-adjacent text.
Preparing snippets for documentation, tickets, commits, or handoff.
Checking a small payload quickly without switching tools.

Developer checks

Run irreversible transforms like minify or obfuscate on a copy.
Keep secrets out of pasted snippets unless the tool explicitly stays local.
Use your normal tests or linter before shipping transformed code.

Good next steps

These links move the current task into a more complete workflow.

Real-world use cases

Grep a deep value out of a giant API response
A 4000-line JSON payload comes back from an API and you need the auth token buried somewhere inside. Paste it, switch to JSON to gron, copy the lines, and run grep -i token over them. Instead of scrolling through nested braces you get json.data.session.refresh_token = "eyJ…"; on one line with its full path. Same trick finds every URL, every id, every email — grep the word, read the path, done.
Diff two JSON files line by line
Structured JSON diffs are noisy because formatting and key order move things around. Run both files through gron and the output is a flat, stable list of path = value lines, so an ordinary line diff (or git diff) shows exactly which leaves changed and where. A reordered object no longer looks like a hundred-line change; only the genuinely different assignments stand out.
Edit a buried value with sed, then rebuild
You need to bump json.config.replicas from 2 to 5 in a config you would rather not hand-edit through three levels of nesting. gron the file, change the one line (by hand or with sed), then ungron it back into valid, pretty-printed JSON. The path syntax makes the edit unambiguous and the round trip guarantees the structure is rebuilt correctly.
Teach or document a JSON shape
When you explain an API response in a doc or a code review, a wall of braces hides the structure. gron lines spell out every path explicitly, so a reader sees json.items[0].price = 9.99; and immediately knows the shape, the types and where each field lives — no mental parsing of indentation required.

Common pitfalls

Expecting gron output to be valid JSON. It is not — it is a list of assignment statements (json.a = 1;). To get JSON back, switch the direction to ungron, which parses those statements and rebuilds the object. Do not feed gron lines into a JSON parser directly.
Hand-editing a gron line into a syntactically broken value. The right side of each line must be a JSON literal, so a string needs its quotes (= "5";) while a bare number is = 5;. Writing = 5 abc; or dropping the quotes on a string makes that line fail to ungron with a value error.
Renaming the root variable on one side only. If you gron with a custom root like data and then try to ungron text that still says json, both work independently, but mixing lines with different roots in one paste rebuilds them onto separate roots. Keep the root consistent across a single document.

Privacy

Both directions — JSON to gron and ungron back to JSON — are plain JavaScript that runs inside your browser tab. The JSON you paste, the gron lines and the rebuilt output never leave the page and are not logged. The one caveat: the shareable URL encodes your input in the query string, so a link pasted into chat records that input in the recipient server's access log. For anything sensitive — tokens, private payloads — use the copy button and paste the text rather than sharing the URL.

FAQ

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gron Converter — JSON to gron and ungron

What this tool does

Tool details

How to use

1. Input

2. Process

3. Copy / Download

How gron Converter (JSON to gron / ungron) fits into your work

Developer jobs

Developer checks

Good next steps

Real-world use cases

Grep a deep value out of a giant API response

Diff two JSON files line by line

Edit a buried value with sed, then rebuild

Teach or document a JSON shape

Common pitfalls

Privacy

FAQ

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