Cookie Transmission Scenario Analysis

This document analyzes cookie transmission scenarios and organizes whether cookies are transmitted based on various SameSite settings and domain attributes. This analysis is based on requests between https://api.hello.dev and https://hello.dev.

Prerequisites

All cookies have the following common options:

• Secure=true: Cookies are transmitted only over HTTPS connections

The browser transmits all SameSite setting cookies only for same-site requests (where origin and target share the same registered domain hello.dev), so there's no blocking due to SameSite here. When a cookie's Domain attribute is specified, the cookie is transmitted to that domain and all its subdomains. In the tables below, ✅ indicates cookie transmission, and 🚫 indicates no transmission.

https://api.hello.dev → https://api.hello.dev

Domain	SameSite	Form GET	Form POST	Fetch GET	Fetch POST
api.hello.dev	Strict	✅	✅	✅¹	✅¹
api.hello.dev	Lax	✅	✅	✅¹	✅¹
api.hello.dev	None	✅	✅	✅¹	✅¹
.hello.dev	Strict	✅	✅	✅¹	✅¹
.hello.dev	Lax	✅	✅	✅¹	✅¹
.hello.dev	None	✅	✅	✅¹	✅¹

https://api.hello.dev → https://*.hello.dev

Domain	SameSite	Form GET	Form POST	Fetch GET	Fetch POST
api.hello.dev	Strict	🚫	🚫	🚫	🚫
api.hello.dev	Lax	🚫	🚫	🚫	🚫
api.hello.dev	None	🚫	🚫	🚫	🚫
.hello.dev	Strict	✅	✅	✅¹	✅¹
.hello.dev	Lax	✅	✅	✅¹	✅¹
.hello.dev	None	✅	✅	✅¹	✅¹

https://api.hello.dev → https://hello.dev

Domain	SameSite	Form GET	Form POST	Fetch GET	Fetch POST
api.hello.dev	Strict	🚫	🚫	🚫	🚫
api.hello.dev	Lax	🚫	🚫	🚫	🚫
api.hello.dev	None	🚫	🚫	🚫	🚫
.hello.dev	Strict	✅	✅	✅¹	✅¹
.hello.dev	Lax	✅	✅	✅¹	✅¹
.hello.dev	None	✅	✅	✅¹	✅¹

https://hello.dev → https://api.hello.dev

Domain	SameSite	Form GET	Form POST	Fetch GET	Fetch POST
hello.dev	Strict	🚫	🚫	🚫	🚫
hello.dev	Lax	🚫	🚫	🚫	🚫
hello.dev	None	🚫	🚫	🚫	🚫
.hello.dev	Strict	✅	✅	✅¹	✅¹
.hello.dev	Lax	✅	✅	✅¹	✅¹
.hello.dev	None	✅	✅	✅¹	✅¹

https://hello.dev → https://*.hello.dev

Domain	SameSite	Form GET	Form POST	Fetch GET	Fetch POST
hello.dev	Strict	🚫	🚫	🚫	🚫
hello.dev	Lax	🚫	🚫	🚫	🚫
hello.dev	None	🚫	🚫	🚫	🚫
.hello.dev	Strict	✅	✅	✅¹	✅¹
.hello.dev	Lax	✅	✅	✅¹	✅¹
.hello.dev	None	✅	✅	✅¹	✅¹

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Footnotes

¹ With credentials (Fetch API requires credentials: include option)

Note: When the domain attribute is specified, cookies are transmitted to the specified domain and all its subdomains.