ParamDiff

ParamDiff — decode, expand, and diff URL query params

A small web app for inspecting and comparing URLs — paste 1–4 URLs, peel back URL-encoding layer by layer, expand nested query strings, and diff query parameters across URLs side by side.

Download

Download index.html — single self-contained file (~150 KB). Open it in any modern browser; no install, no server, no network needed.

See release notes for the changelog and other assets.

How to use

1. Open the app. Either visit a hosted instance, or download index.html from the latest Release and open it in any modern browser. The file is fully self-contained (~150 KB) — no install, no server, no network needed at runtime. Your URLs never leave the page.
2. Paste a URL into the first input. ParamDiff splits it at the first ? and lists every query parameter as its own row.
3. Peel encoded values. Click Decode on any row to apply one decodeURIComponent pass — click again for double-encoded values (%253A → %3A → :). The button disables once nothing further would change.
4. Drill into nested query strings. When a value carries its own params (typical of OAuth returnUrl / redirect_uri), click Expand to split it into indented child rows. Each child has its own Decode/Expand/Reset, so you can recurse arbitrarily deep.
5. Reset. Click Reset to restore the original raw value and collapse any expansion on that row.
6. Compare. Click + Add URL for up to 4 URLs. The Diff section under the inputs lists every parameter key seen across them, with one cell per URL — green when all match, red when they differ, grey when missing in that URL.

Tip: the diff reflects whatever decode/expand state you've applied. To compare two URLs fairly, peel them the same number of times.

How it parses

1. Top-level split at the first ? → base + key=value pairs (no automatic decoding; values are preserved raw so you can choose when to peel).
2. Decode applies decodeURIComponent once. If the result is identical (already fully decoded, or unchangeable), the button disables.
3. Expand is offered when a value contains = plus either a ? or a chain of &-joined key=value pairs with conservative-looking keys (/^[A-Za-z0-9_\-.]+$/). It splits at the first ? (if any), keeps the prefix as nestedBase, and creates child params from the rest.
4. Diff flattens each URL's param tree to { keyPath, value }[], builds a union of keys preserving first-seen order, and renders one row per key with one cell per URL.

Notes / known limits

• Param keys are matched literally for diffing — if URL A uses client_id and URL B uses clientId, they show as separate rows.
• Bare query strings (a=1&b=2 with no ?) are detected by Expand only when keys look conservative — this avoids false positives on prose values.
• Repeated keys (?tag=a&tag=b) keep both, but the diff key path is the same for both, so the second one wins in the per-URL flat map. Rare in practice.
• No persistence — refreshing the page clears all inputs.

Development

Build instructions, project layout, and internals live in DEVELOPMENT.md.

License

MIT — see LICENSE.