Free developer & ad-tech tools

Seven small, focused, browser-only utilities that I built because I needed them in my day job and couldn't find good free alternatives. Everything runs client-side — nothing is uploaded, no signup, no rate limits.

The tools are grouped into two families. The ad-tech tools (ORTB Creative Renderer) are built around OpenRTB and VAST — they exist because debugging programmatic creatives on a real ad slot is painful and slow. The developer tools (JSON, URL, Diff, Escape, Prefix/Suffix, JSON-to-CSV) are the kind of small daily utilities you reach for ten times a day when working with API responses, log files, and data exports.

Each tool has its own page below explaining what it does, who it's for, and how it works under the hood. Or open the live tool directly from the home page.

Ad-tech

ORTB Creative Renderer

Paste a full OpenRTB bid response and render the creative (banner, VAST, native) in a sandboxed iframe. Auto-resolves VAST wrappers, substitutes macros, surfaces vendor and tracker URLs.

Developer

JSON · XML · SQL · HTML

JSON Beautifier & Validator

Pretty-print and validate JSON, XML, SQL, or HTML. Live mode, configurable indent, syntax-error location highlighting. Handles large payloads.

URL

URL Decoder & Encoder

Percent-encoding decode and encode with full charset support: UTF-8, Latin-1, Windows-1251. Per-line batch mode for processing log dumps.

Diff

Online Diff Tool

Side-by-side comparison for JSON, XML, SQL, HTML. Order-independent structural diff for JSON objects, line-level for plain text. Sync-scroll.

Escape

Escape & Unescape

Escape or unescape special characters for JSON, XML, HTML, or SQL strings. Handles Unicode escape sequences, HTML entities, and the SQL quoting rules.

Text

Prefix & Suffix

Add a prefix and/or suffix to every line of a list. Useful for wrapping IDs in quotes for SQL IN clauses, prepending HTTPS to domain lists, batch URL prep.

JSON · CSV

JSON to CSV Converter

Convert JSON arrays to CSV with optional flattening of nested objects. Configurable delimiter (comma, semicolon, tab), header row toggle, downloadable .csv.

Why use these instead of an installed CLI?

Most professional developers have jq, xmllint, diff, and a dozen other CLI tools installed. These tools are not trying to replace that workflow — they exist for the moments when you don't have a terminal in front of you, when you want to share a one-off result with a non-technical colleague, when you need to verify a quick edge case without context-switching, or when you're working on a machine where you don't want to install anything.

The trade-off is intentional: less power than a CLI, but zero install, zero state, and full privacy because nothing leaves the browser tab.

Reading material

Most of the tools above have a directly related article on the blog:

What is OpenRTB? — background for the ORTB Renderer
Understanding VAST tags — wrapper resolution, the bit the renderer actually does for you
Creative debugging in programmatic advertising — what to look for when a creative refuses to render
JSON formatting and validation — beats reading the spec cold
URL encoding explained — why analytics params break, and how to fix them
Ad-tech glossary — fifty terms with non-trivial definitions