About HTTP Header Builder

Compose request headers — output as curl flags and fetch options. Part of the DevTools Surf developer suite. Browse more tools in the Networking collection.

Use Cases

• API developers composing complex request headers for testing
• Frontend devs generating fetch options for authenticated requests
• DevOps engineers building curl commands for monitoring scripts
• Backend devs debugging CORS by inspecting required headers

Tips

• Add multiple headers and export as curl flags at once
• Include Content-Type and Accept headers for API calls
• Output provides both curl flags and fetch options objects

Fun Facts

• HTTP headers were part of the original HTTP/0.9 specification in 1991, but Tim Berners-Lee's first design had no headers at all — just a raw GET request and HTML response.
• The X- prefix for custom headers (X-Request-ID) was deprecated by RFC 6648 in 2012, but it remains so common that most developers still use it by convention.
• HTTP/2, standardized in 2015, compresses headers using HPACK encoding, reducing header overhead by 85-88% compared to HTTP/1.1's plain-text format.

FAQ

What output formats?

curl flags (-H 'Name: value'), fetch options ({headers: {...}}), axios config, raw HTTP request format. Copy whichever matches your workflow.

Does it validate header names?

Common ones with known syntax (Content-Type, Accept) are validated. Custom headers (X-Whatever) pass through as-is.

Can I set cookies?

Yes — Cookie header is a special case. Multi-value cookies, attributes, and SameSite rules are handled correctly.

What's the max header size?

No hard limit in the builder. Real servers cap total header size around 8-16KB. The tool warns if you approach typical limits.