SourceMap header

Baseline Widely available

This feature is well established and works across many devices and browser versions. It’s been available across browsers since January 2020.

The HTTP SourceMap response header provides the location of a source map for the resource.

The HTTP SourceMap header has precedence over a source annotation (sourceMappingURL=path-to-map.js.map), and if both are present, the header URL is used to resolve the source map file.

Header type Response header
Forbidden request header No

Syntax

http
SourceMap: 
X-SourceMap:  (deprecated)

Directives

A relative (to the request URL) or absolute URL pointing to a source map file.

Examples

Linking to a source map using the SourceMap header

The following response contains an absolute path in the SourceMap header.

http
HTTP/1.1 200 OK
Content-Type: text/javascript
SourceMap: /path/to/file.js.map

Developer tools use the source map to reconstruct the original source from the optimized JavaScript returned in the response, allowing developers to debug the original code rather than the format that has been optimized for sending.

Specifications

Specification
Source map format specification
# sec-linking-http-header

Browser compatibility

See also