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HTTP Header Parser & Format Validator

Parse Name: value lines, count fields, and flag lines that lack a colon.

Page updated 2026-09-04.

HTTP Header Parser & Format Validator visual
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One header per line.

Calculated Results

Header count

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Splitting raw header text into name/value pairs

Three raw lines -- 'Host: www.veomark.com', 'Content-Type: text/html', and 'Cache-Control: max-age=600' -- parse into 3 headers with names Host, Content-Type, Cache-Control, and every line confirmed to follow the standard 'Name: value' format.

Header names are conventionally case-insensitive per the HTTP specification (Content-Type and content-type refer to the same header), though this parser preserves whatever capitalization appears in the raw text you paste in, rather than normalizing it.

The colon-and-space separator ('Name: value') is the standard format this parser expects -- each line is split on the first colon, with everything after it (trimmed) treated as the value, which correctly handles values that themselves contain colons (like a Cache-Control directive with a time value).

What this simple line-based parser doesn't handle

Line-based colon split. Folded headers and HTTP/2 pseudo-headers are not modeled. Older HTTP/1.1 allowed 'folded' headers spanning multiple lines (a continuation line starting with whitespace) -- a legal but now-deprecated format this line-by-line parser doesn't reconstruct into a single logical header.

HTTP/2 and HTTP/3 use pseudo-headers (like :method, :path, :authority) with a leading colon as part of the name itself, a different structural convention than HTTP/1.1's Name: value format -- this parser is built around the HTTP/1.1 text format, not binary HTTP/2 framing.

This checks structural format only (does each line look like Name: value) -- it doesn't validate whether a given header name is a real, registered HTTP header or whether its value is semantically valid for that header.

Related HTTP debugging tools

Once headers are parsed, checking the response status code they came with is a common next step -- the HTTP Status Code Lookup covers that.

If the User-Agent header value itself needs breaking down into browser, OS, and device info, the User-Agent String Parser handles that specific header's content.

Frequently Asked Questions (FAQ)

How does the parser know where the header name ends and the value begins?

It splits each line at the first colon character, treating everything before it as the name and everything after (trimmed of leading whitespace) as the value -- which correctly handles values that contain additional colons, like a time-based directive.

Does header name capitalization matter?

Not per the HTTP specification -- header names are case-insensitive, so Content-Type and content-type are the same header. This parser preserves whatever capitalization you paste in rather than normalizing it to a canonical form.

Does this handle multi-line (folded) headers?

No. Line-based colon split. Folded headers and HTTP/2 pseudo-headers are not modeled. Legacy HTTP/1.1 folded-header continuation lines aren't reconstructed into a single header value -- each line is parsed independently.

Does this work for HTTP/2 pseudo-headers like :method or :path?

Not natively -- HTTP/2 pseudo-headers use a different structural convention (a leading colon as part of the name) than the HTTP/1.1 'Name: value' text format this parser is built around.

Does 'all lines have Name: value' mean the headers are semantically valid?

No, only that each line's structure matches the expected format. This parser doesn't check whether a header name is an officially registered HTTP header or whether its value makes sense for that specific header.

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