Synchronize cookies
Cookie synchronization is a Headerly action component available to modifyHeaders profiles. It reads a selected browser cookie and appends name=value to the outgoing Cookie header.
Fields
| Field | Purpose |
|---|---|
| Domain | Exact domain recorded for the selected cookie, including any leading dot |
| Path | Exact cookie path |
| Name | Cookie name |
| Value | Current value copied from the browser cookie store |
Domain and host-only scope
Chrome exposes both a domain string and a hostOnly boolean for each cookie. Chromium's cookie representation encodes the same host-only distinction in the domain string:
| Domain value | Chrome property | Scope |
|---|---|---|
example.com | hostOnly: true | Matches only the exact example.com host |
.example.com | hostOnly: false | Domain cookie that can match example.com and its subdomains |
The leading dot does not represent a separate hostname property. It is Chromium's domain-string representation of the cookie's hostOnly scope. Headerly stores the exact domain value returned by Chrome instead of storing hostOnly separately.
For this reason, the Domain value must exactly match the Domain column in Developer Tools > Application > Cookies. If that column contains .example.com, the dot is part of Headerly's cookie identity and must not be omitted.
Cookie identity
Headerly uses domain + path + name as the composite identity of a synchronized cookie. All three fields are required because cookies with the same name can coexist under different domains or paths. The exact domain string also distinguishes a host-only cookie from a domain cookie, so these identities are different:
example.com + / + session
.example.com + / + sessionHeaderly uses this composite identity when reading the current value and processing cookie-change events. If the domain, leading dot, path, or name differs, Headerly treats it as another cookie. When no exact match exists, the synchronized value becomes empty and no Cookie header modification is generated.
Empty names, paths, domains, or values do not produce a header modification. Multiple profile items may intentionally use the same composite identity; they will follow the same browser cookie.
Synchronization
Headerly reads configured cookie values when the extension starts, when cookie permission is granted, and when cookie identities change. It also listens for cookie changes.
Deleting or expiring a cookie clears the stored value. Chrome can report an overwrite as a removal followed by an insertion; Headerly retains the latest observed change.
Export and import
Headerly clears synchronized Cookie values when generating exported JSON, downloaded profiles, and share links. Domain, Path, and Name remain in the export as the Cookie identity.
After import, Headerly uses that identity to read the matching Cookie from the current user's browser. Different users can therefore use the same exported profile while Headerly synchronizes a different local value for each user. If no exact local match exists, Value remains empty and no Cookie header modification is generated.
Permission
This feature requires the optional cookies permission and host access for the cookie's domain. See Permissions.
Limitations
The Chrome Cookies API can distinguish cookie stores and partitioned cookies with storeId and partitionKey. Headerly does not store those fields. Therefore the identity is not sufficient to distinguish every Cookies Having Independent Partitioned State (CHIPS, also known as ), or regular-versus-incognito case.
Headerly explicitly appends the selected value to matching requests. Restrict the profile conditions carefully; the source cookie's Domain, Path, SameSite, and Secure attributes do not define the target requests selected by the Headerly profile.