When configured, by default all requests to the site will be logged. To conditionally skip some requests from logging, use the [`skip_log` directive](/docs/caddyfile/directives/skip_log).
Since Caddy v2.5, by default, headers with potentially sensitive information (`Cookie`, `Set-Cookie`, `Authorization` and `Proxy-Authorization`) will be logged with empty values. This behaviour can be disabled with the [`log_credentials`](/docs/caddyfile/options#log-credentials) global server option.
- **format** describes how to encode, or format, the logs. See [Format modules](#format-modules) below. Default: `console` if `stdout` is detected to be a terminal, `json` otherwise.
- **roll_size** is the size at which to roll the log file. The current implementation supports megabyte resolution; fractional values are rounded up to the next whole megabyte. For example, `1.1MiB` is rounded up to `2MiB`. Default: `100MiB`
- **roll_keep_for** is how long to keep rolled files as a [duration string](/docs/conventions#durations). The current implementation supports day resolution; fractional values are rounded up to the next whole day. For example, `36h` (1.5 days) is rounded up to `48h` (2 days). Default: `2160h` (90 days)
- **dial_timeout** is how long to wait for a successful connection to the log socket. Log emissions may be blocked for up to this long if the socket goes down.
**A note about Common Log Format (CLF):** CLF clashes with modern structured logs. To transform your access logs into the deprecated Common Log Format, please use the [`transform-encoder` plugin](https://github.com/caddyserver/transform-encoder).
Nested fields can be referenced by representing a layer of nesting with `>`. In other words, for an object like `{"a":{"b":0}}`, the inner field can be referenced as `a>b`.
The following fields are fundamental to the log and cannot be filtered because they are added by the underlying logging library as special cases: `ts`, `level`, `logger`, and `msg`.
Masks IP addresses in the field using a CIDR mask, i.e. the number of bits from the IP to retain, starting from the left side. If the field is an array of strings (e.g. HTTP headers), each value in the array is masked. The value may be a comma separated string of IP addresses.
There is separate configuration for IPv4 and IPv6 addresses, since they have a different total number of bits.
Most commonly, the fields to filter would be `request>remote_ip` for the directly connecting client, or `request>headers>X-Forwarded-For` if behind a reverse proxy.
Marks a field to have one or more actions performed, to manipulate the query part of a URL field. Most commonly, the field to filter would be `uri`. The available actions are:
```caddy-d
<field> query {
delete <key>
replace <key><replacement>
hash <key>
}
```
- **delete** removes the given key from the query.
- **replace** replaces the value of the given query key with **replacement**. Useful to insert a redaction placeholder; you'll see that the query key was in the URL, but the value is hidden.
- **hash** replaces the value of the given query key with the first 4 bytes of the SHA-256 hash of the value, lowercase hexadecimal. Useful to obscure the value if it's sensitive, while being able to notice whether each request had a different value.
##### cookie
Marks a field to have one or more actions performed, to manipulate a `Cookie` HTTP header's value. Most commonly, the field to filter would be `request>headers>Cookie`. The available actions are:
```caddy-d
<field> cookie {
delete <name>
replace <name><replacement>
hash <name>
}
```
- **delete** removes the given cookie by name from the header.
- **replace** replaces the value of the given cookie with **replacement**. Useful to insert a redaction placeholder; you'll see that the cookie was in the header, but the value is hidden.
- **hash** replaces the value of the given cookie with the first 4 bytes of the SHA-256 hash of the value, lowercase hexadecimal. Useful to obscure the value if it's sensitive, while being able to notice whether each request had a different value.
If many actions are defined for the same cookie name, only the first action will be applied.
Marks a field to have a regular expression replacement applied at encoding time. If the field is an array of strings (e.g. HTTP headers), each value in the array has replacements applied.
The regular expression language used is RE2, included in Go. See the [RE2 syntax reference](https://github.com/google/re2/wiki/Syntax) and the [Go regexp syntax overview](https://pkg.go.dev/regexp/syntax).
In the replacement string, capture groups can be referenced with `${group}` where `group` is either the name or number of the capture group in the expression. Capture group `0` is the full regexp match, `1` is the first capture group, `2` is the second capture group, and so on.
Marks a field to be replaced with the first 4 bytes (8 hex characters) of the SHA-256 hash of the value at encoding time. If the field is a string array (e.g. HTTP headers), each value in the array is hashed.
Useful to obscure the value if it's sensitive, while being able to notice whether each request had a different value.
Mask the remote address from the request, keeping the first 16 bits (i.e. 255.255.0.0) for IPv4 addresses, and the first 32 bits from IPv6 addresses. (Note that prior to Caddy v2.5, the field was named `remote_addr`, but is now `remote_ip`):
