Structure security rules
Firestore Security Rules allow you to control access to documents and collections in your database. The flexible rules syntax allows you to create rules that match anything, from all writes to the entire database to operations on a specific document.
This guide describes the basic syntax and structure of security rules. Combine this syntax with security rules conditions to create complete rulesets.
Service and database declaration
Firestore Security Rules always begin with the following declaration:
service cloud.firestore {
match /databases/{database}/documents {
// ...
}
}
The service cloud.firestore declaration scopes the rules to
Firestore, preventing conflicts between Firestore Security Rules and
rules for other products such as Cloud Storage.
The match /databases/{database}/documents declaration specifies that rules should
match any Firestore database in the project. Currently each project
has only a single database named (default).
Basic read/write rules
Basic rules consist of a match statement specifying a document path and
an allow expression detailing when reading the specified data is allowed:
service cloud.firestore {
match /databases/{database}/documents {
// Match any document in the 'cities' collection
match /cities/{city} {
allow read: if <condition>;
allow write: if <condition>;
}
}
}
All match statements should point to documents, not collections. A match
statement can point to a specific document, as in match /cities/SF or use wildcards
to point to any document in the specified path, as in match /cities/{city}.
In the example above, the match statement uses the {city} wildcard syntax.
This means the rule applies to any document in the cities collection, such as
/cities/SF or /cities/NYC. When the allow expressions in the match statement are
evaluated, the city variable will resolve to the city document name,
such as SF or NYC.
Granular operations
In some situations, it's useful to break down read and write into more
granular operations. For example, your app may want to enforce different
conditions on document creation than on document deletion. Or you may want to
allow single document reads but deny large queries.
A read rule can be broken into get and list, while a write rule can
be broken into create, update, and delete:
service cloud.firestore {
match /databases/{database}/documents {
// A read rule can be divided into get and list rules
match /cities/{city} {
// Applies to single document read requests
allow get: if <condition>;
// Applies to queries and collection read requests
allow list: if <condition>;
}
// A write rule can be divided into create, update, and delete rules
match /cities/{city} {
// Applies to writes to nonexistent documents
allow create: if <condition>;
// Applies to writes to existing documents
allow update: if <condition>;
// Applies to delete operations
allow delete: if <condition>;
}
}
}
Hierarchical data
Data in Firestore is organized into collections of documents, and each document may extend the hierarchy through subcollections. It is important to understand how security rules interact with hierarchical data.
Consider the situation where each document in the cities collection contains a
landmarks subcollection. Security rules apply only at the matched path, so the
access controls defined on the cities collection do not apply to the
landmarks subcollection. Instead, write explicit rules to control access
to subcollections:
service cloud.firestore {
match /databases/{database}/documents {
match /cities/{city} {
allow read, write: if <condition>;
// Explicitly define rules for the 'landmarks' subcollection
match /landmarks/{landmark} {
allow read, write: if <condition>;
}
}
}
}
When nesting match statements, the path of the inner match statement is always
relative to the path of the outer match statement. The following rulesets
are therefore equivalent:
service cloud.firestore {
match /databases/{database}/documents {
match /cities/{city} {
match /landmarks/{landmark} {
allow read, write: if <condition>;
}
}
}
}
service cloud.firestore {
match /databases/{database}/documents {
match /cities/{city}/landmarks/{landmark} {
allow read, write: if <condition>;
}
}
}
Recursive wildcards
If you want rules to apply to an arbitrarily deep hierarchy, use the
recursive wildcard syntax, {name=**}. For example:
service cloud.firestore {
match /databases/{database}/documents {
// Matches any document in the cities collection as well as any document
// in a subcollection.
match /cities/{document=**} {
allow read, write: if <condition>;
}
}
}
When using the recursive wildcard syntax, the wildcard variable will contain the
entire matching path segment, even if the document is located in a deeply nested
subcollection. For example, the rules listed above would match
a document located at /cities/SF/landmarks/coit_tower, and the value of
the document variable would be SF/landmarks/coit_tower.
Note, however, that the behavior of recursive wildcards depends on the rules version.
Version 1
Security rules use version 1 by default. In version 1, recursive wildcards
match one or more path items. They do not match an empty path, so
match /cities/{city}/{document=**} matches documents in subcollections but
not in the cities collection, whereas match /cities/{document=**} matches
both documents in the cities collection and subcollections.
Recursive wildcards must come at the end of a match statement.
Version 2
In version 2 of the security rules, recursive wildcards match zero or more path
items. match/cities/{city}/{document=**} matches documents in any
subcollections as well as documents in the cities collection.
You must opt-in to version 2 by adding rules_version = '2'; at the top of
your security rules:
rules_version = '2';
service cloud.firestore {
match /databases/{database}/documents {
// Matches any document in the cities collection as well as any document
// in a subcollection.
match /cities/{city}/{document=**} {
allow read, write: if <condition>;
}
}
}
You can have at most one recursive wildcard per match statement, but in version 2, you can place this wildcard anywhere in the match statement. For example:
rules_version = '2';
service cloud.firestore {
match /databases/{database}/documents {
// Matches any document in the songs collection group
match /{path=**}/songs/{song} {
allow read, write: if <condition>;
}
}
}
If you use collection group queries, you must use version 2, see securing collection group queries.
Overlapping match statements
It's possible for a document to match more than one match statement. In the
case where multiple allow expressions match a request, the access is allowed
if any of the conditions is true:
service cloud.firestore {
match /databases/{database}/documents {
// Matches any document in the 'cities' collection.
match /cities/{city} {
allow read, write: if false;
}
// Matches any document in the 'cities' collection or subcollections.
match /cities/{document=**} {
allow read, write: if true;
}
}
}
In the example above, all reads and writes to the cities collection will be
allowed because the second rule is always true, even though the first
rule is always false.
Security rule limits
As you work with security rules, note the following limits:
| Limit | Details |
|---|---|
Maximum number of exists(), get(), and getAfter() calls per request |
Exceeding either limit results in a permission denied error. Some document access calls may be cached, and cached calls do not count towards the limits. |
Maximum nested match statement depth |
10 |
Maximum path length, in path segments, allowed within a set of nested
match statements |
100 |
Maximum number of path capture variables allowed within a set of
nested match statements |
20 |
| Maximum function call depth | 20 |
| Maximum number of function arguments | 7 |
Maximum number of let variable bindings per function |
10 |
| Maximum number of recursive or cyclical function calls | 0 (not permitted) |
| Maximum number of expressions evaluated per request | 1,000 |
| Maximum size of a ruleset | Rulesets must obey two size limits:
|
Next steps
- Write custom security rules conditions.
- Read the security rules reference.