About

About rangelab

A free, open tool for HTTP partial content — the byte-range mechanism behind resumable downloads, media seeking, and object-store reads.

HTTP lets a client ask for part of a resource with a Range header, and the server answers with 206 Partial Content and a Content-Range describing the slice. The rules are small but full of edge cases — suffix ranges, clamping, multi-range multipart bodies, the 416 response — and an off-by-one quietly breaks downloads and video players. Instead of guessing, paste the header and the size and let rangelab resolve it.

rangelab takes a Range request header and a resource size and applies the RFC 9110 rules: it parses each byte-range spec (integer, open-ended, or suffix), resolves the real byte intervals (with clamping and satisfiability), and reports the exact response — 206 single, 206 multipart/byteranges, 416, or an ignored-Range 200 — with the precise Content-Range, Content-Length, and Accept-Ranges headers. A second mode validates a Content-Range response value. Every figure follows a disclosed method, runs entirely in your browser, and makes no live request. It is informational; confirm against your real server.

It covers the cases people trip on: bytes=-500 being the LAST 500 bytes (not the first), a last-byte-pos beyond the end being clamped, first ≥ size giving a 416 with Content-Range: bytes */total, several ranges producing a multipart/byteranges body, and a malformed Range being ignored for a plain 200.

Informational developer tool. It resolves the RFC 9110 rules statically from what you paste and makes no live request, so confirm against your real server, proxy, or CDN. Open the tool →