How to use Yellorn

Paste text or drop a file

Open the editor and paste JSON, JSON Lines, XML, YAML, TOML, CSV, ASCII tables, SQL, or Python. Yellorn auto-detects the format and switches once it’s confident — or pick one yourself from the toolbar’s format selector.

Or drag a file onto the editor. Binary files decode locally in your browser — Parquet, Apache Arrow / Feather, Excel, MessagePack, CBOR, Protobuf, BSON, gzip — as do AI model files (Safetensors, GGUF), ComfyUI PNGs, and X.509 certificates (PEM, DER, PKCS#12 / PFX, PKCS#7, CSR). Nothing is uploaded.

The visualizer updates as you type: CSV, Parquet, and Excel open as a table; JSON, XML, and YAML open as a tree.

Repair broken input with Smart Format

Press Cmd + Shift + F (or Ctrl + Shift + F on Windows / Linux) to run Smart Format. It runs the format’s recovery ladder — 29 fix passes across JSON, XML, YAML, and CSV — then pretty-prints the result.

Every applied fix is labelled in the status bar (Auto-fixed: trailing-commas, single-quotes) so you consent to every transformation before publishing.

Convert between formats

Click Convert to… in the editor toolbar to swap the active format. JSON ↔ XML ↔ YAML ↔ CSV ↔ Python is supported with structural-compatibility checks; lossy conversions surface a warning toast first. One Cmd + Z reverts both the text and the format together.

Publish a payload as a mock REST endpoint

Sign in (free) and click Publish. Yellorn returns a global HTTPS URL anyone can GET / POST / PUT / PATCH / DELETE. The owner-only portal at /webhook/<slug> shows every request — method, headers, body, source IP, and timestamp.

Configure the canned response status code (200 / 401 / 429 / 500) from the portal to simulate failure paths without redeploying anything.

Make the mock response dynamic

A published webhook can return live data instead of a fixed string. Wrap a Python-flavoured expression in {{ }} and it renders fresh on every request: {{ uuid4() }} for a new id, {{ now() }} for the current timestamp, {{ randint(1, 100) }} or {{ choice("active", "pending") }} for random values, and {{ request.ip }} to echo the caller.

Use the Insert token button for a searchable picker with live previews, or just start typing inside a token for in-editor autocomplete. The same tokens work in Request Sender bodies, URLs, and headers.

Dispatch outbound HTTP requests

Open Request Sender from the account rail, compose a request (method, URL, headers, auth, body), and save it as a template for reuse. Every dispatch is logged with full response details for 8 hours.

Search with JMESPath

Open the search bar in the visualizer and type a JMESPath expression — for example, users[?age > `30`].name. The tree filters live with match counts and Prev/Next navigation.

Back up your tabs across devices

Cloud Backup lives in Settings: click Back up to Cloud to save your open tabs, then Restore from Cloud on any other signed-in browser. Tabs over your size quota are skipped, and a usage bar shows how much room you have left.

Normalize copy-pasted lists with Clean List

Paste a messy list — one item per line, padded comma-separated values, a single-column SQL or Markdown table, or a bracketed array — then open the Format menu in the editor toolbar and choose Clean List (under Minify). Yellorn collapses it to a compact comma list, ready to paste into a SQL IN (…) clause or anywhere else that needs tidy values.

Compare two payloads side-by-side

Click Compare in the tab bar footer, pick exactly two tabs, then Run Comparison (or right-click a tab and choose Compare with the active tab). Yellorn opens Monaco’s read-only diff editor with both payloads. JSON content is key-sorted before diffing so key reorderings don’t pollute the output — only real structural differences appear. Useful for API response regression testing, fixture consistency checks, and customer-payload triage.