HTTP Range Header Builder

How to use

1. 1Pick a mode at the top: Parse Range to inspect a pasted Range request header, Build Range to compose one from start and end byte positions, or Parse Content-Range to read a server's 206 or 416 response.
2. 2In Parse mode, paste a Range header (Range: prefix is optional). Set the optional resource size in bytes and the parser resolves open-ended and suffix ranges to exact byte counts and percentages.
3. 3In Build mode, add one row per range and choose the kind (bounded first-last, open-ended first-, or suffix -N). Fill in the byte positions. The generated header line, curl command, and fetch snippet update live.
4. 4In Content-Range mode, paste a Content-Range response header to see the byte window, the complete length, the coverage bar, and a follow-up Range header for the bytes after the slice returned.
5. 5Use the sample chips to load real-world examples: first 500 bytes, last 500 bytes, from byte N to end, multipart head and tail, video seek, and resumable retry.
6. 6Read the warnings: overlapping ranges, too many parts, ranges past the end, and 416 unsatisfied responses are flagged with the exact rule violated and the fix to apply.

About this tool

HTTP Range Header Builder helps you read, write, and reason about HTTP byte range requests directly in your browser. The Range request header (RFC 9110 section 14.2, formerly RFC 7233) lets a client ask the server for a slice of a resource instead of the whole thing, and is what every video seek bar, every resumable download manager, and every S3, CloudFront, Cloudflare, Backblaze B2, or Google Cloud Storage object client uses to fetch a chunk on demand. The tool implements three modes that cover the full workflow. Parse mode takes a pasted Range header (with or without the literal Range: prefix) and breaks it into one row per byte range. Each row is annotated with its kind (bounded first-last, open-ended first-, or suffix -N), the resolved first and last byte positions, and the effective byte length; the parser flags grammar mistakes that real servers reject (a non-numeric first or last, a last byte less than the first, an empty piece from a stray comma, missing or non-bytes unit), and warns about overlapping ranges, duplicates, and the small-N rule that Apache, IIS, and CloudFront use to mitigate the byte-range amplification attack. Provide an optional resource size and the open-ended and suffix ranges are resolved to exact byte counts and per-range percentages. Build mode is a small form that composes one or more ranges and emits the canonical header line plus a copy-ready curl command and a fetch snippet so you can drop the result straight into a script. The builder rejects ranges that start past the end of a known resource size, warns when the last byte falls past the end (the server will clamp), and reports the total bytes requested and the share of the resource covered. Content-Range mode parses the matching server response: the normal bytes first-last/total form (which accompanies 206 Partial Content), the bytes first-last/* form for live streams where the total is still unknown, and the bytes */total form that 416 Range Not Satisfiable uses to tell the client the size of the resource so it can retry with a valid range. The result panel shows the byte window, the complete length, the percentage of resource covered, a coverage bar visualizing the slice inside the whole resource, and a ready-made follow-up Range header that asks for the bytes after the last one returned. A short reference section summarizes the six patterns developers actually use (bounded, open-ended, suffix, multipart, 206, and 416) with one canonical example each. Everything runs locally; the headers, ranges, and resource sizes you paste here never leave your device.

Free to use. Works in your browser. No signup, no login.