Features in this color are provided by optional plugins.
Overview
Caddy is essentially a configuration management system that can run various apps like an HTTP server, TLS certificate manager, PKI facilities, and more. It can be extended with plugins known as config modules.
Caddy sports a flexible and powerful HTTP reverse proxy, on-line configuration API, and a robust, production-ready static file server, and serves all sites over HTTPS by default with automagic TLS certificates.
Overall program technical specifications
Language
The language choice is crucial for a web server. Language impacts development speed and ease, performance, testing, deployment complexity, ecosystem reliability, dependencies, tooling, error handling and reliability, and much, much more. Go offers strong advantages in all these areas, allowing for rapid development, robust production performance, and high scalability.
Go
Memory safety guarantees
Most servers (NGINX, Apache, HAProxy, etc.) and their dependencies are written in C, which are vulnerable to catastrophic memory safety bugs (such as buffer overflows) like Heartbleed. Go programs like Caddy are impervious to a whole class of security vulnerabilities.
Strong
Build artifacts
Caddy compiles directly to native CPU instructions. There is no interpreter required; and many instructions are architecture-optimized. Static binaries are also more secure because there is no dynamic linking.
Platform-native static binary
Runtime dependencies
Caddy is statically compiled. Dynamically-linked applications can easily break in production and may be less secure as shared executable resources are loaded from various places around the system. Generally, Caddy binaries do not necessarily require external libraries — not even libc.
None
Compile time
On consumer hardware, standard Caddy builds compile in just a few seconds. This is crucial for rapid iteration, plugin development, and low-cost deployments. Other servers written in C/C++ can take several minutes.
~30 seconds cold build, ~2 seconds hot
Deployment environments
Caddy can go practically anywhere and be deployed a variety of ways. In general, upgrading is as simple as replacing the binary.
Command line interface
System service
Containers
Kubernetes
Embedded
Supply chain and releases
Go modules verify the integrity of our dependencies and we cryptographically sign our release artifacts so you know what you can trust.
Cryptographically verified
Operating systems
Caddy runs on every major platform for which Go compiles.
Linux
Windows
macOS
FreeBSD
OpenBSD
NetBSD
Android
Microarchitectures
Run Caddy with native code on numerous CPU platforms.
Go's runtime optimizes scheduled CPU time in smarter ways than the operating system can using lightweight user-space threads called goroutines. Caddy utilizes all CPU cores and easily handles hundreds of thousands of requests per second.
Goroutines (epoll + kqueue)
Plugin model
Caddy can be extended by compile-time plugins, which compile as native code, in a way that cannot be broken during deployments or by system upgrades. With no IPC or RPC calls, Caddy extensions perform equally well with native code.
Compile-time static
High-level capabilities
Configuration changes
With zero-downtime graceful reloads, Caddy's configuration can be changed while it is running. It's programmable/scriptable for powerful automation.
RESTful HTTP API
Config files
Secure remote access
App modules
Top-level configuration structures are called app modules, or Caddy apps. They provide the bulk of Caddy's functionality. Anyone can write app modules, and Caddy comes with several standard apps built-in.
HTTP
TLS
PKI
Events
Raw TCP & UDP
SSH
PHP
Dynamic DNS
Security
Process supervision
Profiling
Logs
All Caddy modules use Caddy's centralized logging facilities. Caddy's logging can be configured as to format, verbosity, output, and more.
Leveled
Structured
High efficiency, zero-allocation
Extensible
Delete, filter, redact, and censor fields
IP masking
Hash values
Regex replacement
Storage
Assets and state, including certificates and OCSP staples, are stored in configurable storage backends. In fact, multiple instances of Caddy configured with the same storage are considered part of a cluster and can coordinate automatically.
File system
Embedded (in-memory)
Postgres
Redis
Vault
Consul
Command line interface
Caddy's CLI is not only useful—it's helpful. While most server CLIs merely run the process and reload config, Caddy's CLI goes the extra lightyear to help make administering your modern web server a breeze.
Plugins can register their own subcommands to extend Caddy's CLI.
Command help
If you misspell a command or flag, miss an argument, or don't know the subcommand, help text is automatically printed. You can also access overall command help or subcommand help with caddy help or -h.
Built-in, automatic (man pages can also be generated)
Admin API wrappers
Several subcommands use administration API endpoints for use with the CLI to help you perform common tasks like loading config from files or stopping the server.
Adapt config to JSON
Start the server, optionally with config
Gracefully reload configuration
Stop the server
Binary utilities
Since custom builds of Caddy are so common, several commands exist to help you manage and get detailed information about your build.
Detailed build metadata
List installed config modules
List dependencies
Add and remove plugin packages
Print the version
Upgrade the Caddy binary
Configuration utilities
If you choose to use configuration files, Caddy's CLI helps you manage them.
Format Caddyfile
Validate configuration
List dependencies
Add and remove plugin packages
Print the version
Module utilities
Modules may register their own subcommands to provide common functionality that can be utilized without a config document.
Static file server
HTTP reverse proxy
Static HTTP responses (templateable)
Storage import/export (backup/restore)
Hash password for use with HTTP basic auth
Export file browse template
Integration utilities
Several subcommands can help you integrate Caddy into your shell environment.
Generate shell completion script
Print the environment
Generate man pages
Install Caddy-managed root CA into trust stores
Remove Caddy-managed root CA from trust stores
System signals
Caddy has support for common operating system signals/interrupts, with subtle differences in behavior for each one.
Whether Caddy exits successfully or with an error, the exit code can give a hint to your process supervisor or script how to handle that.
Configuration
We've designed Caddy so that its configuration not only provides access to features, but it IS a feature in and of itself.
No more quibbling over which config file format is the best: use whatever you want! Caddy's config adapters allow you to use whatever config format you prefer.
Native config format
Caddy's native configuration format is ubiquitous: it has tooling in nearly every operating system, platform, programming language, and API ecosystem. Almost all other formats can be translated down into JSON, which balances human readability and programmability. You'll find it a powerful ally of your web server.
JSON
Config adapters
You can always write your config in another format and with config adapters, Caddy will implicitly translate it into JSON for you so you can work with what you like.
Caddyfile
JSON 5
JSON-C
NGINX Conf
YAML
CUE
TOML
HCL
Dhall
MySQL
Human-friendly config
The Caddyfile is most users' favorite way to write their web server config by hand because its syntax is forgiving while also being designed with a structure that makes it easy to read and write. It is translated to JSON automatically.
Caddyfile
Export
Caddy's administration API allows you to have runtime access to the current configuration in JSON format with a simple GET request.
Config API
Caddy receives its configuration through an API endpoint, which can accept JSON or any other format it has a config adapter for.
Config files
If you prefer normal shell commands for managing configuration, Caddy's CLI wraps the API endpoints for you.
Automatic HTTPS
Our flagship feature, powered by CertMagic. Caddy is the first and only major server that enables HTTPS by default, and automatically procures and renews certificates for all your sites.
Fully-native, integrated auto-HTTPS is far superior to any solution that requires external tooling or cron jobs. Caddy's certificate maintenance is the best in the industry because it is more robust, reliable, and scalable than any other solution. Caddy simplifies your infrastructure instead of complexifying it.
Sure, you can try deploying 100,000 sites with Certbot and a cron job—but if that doesn't fall over by itself, the web server will. Only Caddy is designed to massively scale TLS certificates both horizontally and vertically.
Never manually generate a CSR again. Never click a link in an email to download a certificate. Never (mis)configure your web server to use them. Never miss reminders to renew your certificates, one-by-one, every few months before they expire. You won't even have to think about certificates or TLS.
It's truly automagic.
Compliance
Caddy's TLS defaults are secure without any additional configuration, and passes compliance tests across various industries.
PCI DSS compliant
NIST compliant
HIPAA compliant
Industry best practices
On-Demand TLS
Serving domains that aren't yours? Or have lots of them? No problem! With just a few lines of config, On-Demand TLS gets certificates dynamically during TLS handshakes, scaling your deployments to tens of thousands of certs. This functionality is exclusive to Caddy.
Certificate issuers
Get certificates from any issuing authority in a way compatible with them. Certificate issuers take a CSR and return a certificate resource. Most sites will simply use ACME to get certificates. But Caddy can also issue its own self-signed certificates for internal use, testing, or development. Caddy's issuer sources are pluggable, so Caddy can automate certificates from any issuer modules.
ACME
Internal (self-signed)
Microsoft Active Directory Certificate Services
Certificate managers
Unlike issuers, which take a CSR and return a certificate that Caddy has to manage, certificate managers are modules that can return always-valid certificates on-demand; that is, they are managing the certificates for us. Caddy can get interface with HTTP endpoints or Tailscale to get certificates in this manner, with other ways available through plugins.
HTTP
Tailscale
Cluster coordination
Across all Caddy instances configured with the same storage, Caddy automatically coordinates and shares resources across the cluster. This includes certificate operations and the certificates themselves, OCSP staples, and session ticket keys. This results in reduced latency for your clients and higher scalability.
Obtaining & renewing certificates
Loading existing certificates
OCSP staples
Session ticket keys (STEKs)
Redirect HTTP to HTTPS
By default, HTTP requests will be redirected to HTTPS.
Automatic redirects
OCSP
OCSP indicates when certificates are revoked. Servers should staple OCSP responses to certificates to provide clients with better security and privacy. Caddy is the first and only server to do this automatically and by default. It also caches responses to weather OCSP responder outages, and shares them across its cluster. This can all be disabled if needed.
Automatic OCSP stapling with caching
Must-Staple
Caddy can obtain certificates that force OCSP stapling if the CA supports it. This may grant a higher degree of security in the case of revocation.
Revocation handling
Revoked certificates automatically get replaced. Because Caddy staples and refreshes OCSP responses, it can detect if your certificate has been revoked, and if so, it will replace i
Session ticket hardening
TLS connections are pointless if an attacker steals the key to encrypt session tickets. Caddy has been academically cited as the only server to rotate these keys regularly to limit attack windows.
Automatic STEK rotation
Key types
You can customize the type of key used for your certificates.
Ed25519
ECDSA P256
ECDSA P384
RSA 2048
RSA 4096
Certificate lifetimes
Most ACME clients assume 90-day certificates, or don't expect certificates shorter than 7 days. Caddy can successfully manage certificates with lifetimes on the order of hours and minutes.
Instead of hard-coding a certain age before renewing, Caddy computes the age relative to the lifespan of each certificate, called a Renewal Window Ratio. By default, Caddy renews certificates after 2/3 of their usable lifetime. This ratio works for most validity periods, but can be adjusted.
Any lifetime
Intelligent error handling
If Caddy can't get a certificate, errors are logged and Caddy will backoff exponentially and retry as long as needed until it succeeds (typically up to 30 days but could be longer). Caddy makes every reasonable effort to keep your certificate renewed.
Exponential backoff
Built-in throttling
Caddy conforms to best practices and doesn't blast CAs with requests for certificates; instead, each order is carefully timed to avoid overwhelming CA servers.
ACME
Caddy's ACME client is best-in-class, with higher reliability and more production experience than any other integrated ACME client available today. Caddy has been using ACME since before the public availability of Let's Encrypt, and Caddy works with any ACME-compatible CA.
Compatibility
Some ACME clients are only tested with Let's Encrypt. Caddy is guaranteed compatible with all ACME-capable CAs.
All RFC 8555-compliant certificate authorities, such as:
Let's Encrypt
ZeroSSL
Google Trust Services
BuyPass
DigiCert
GlobalSign
SSL.com
Smallstep
Test endpoints
By default, Caddy will fall back to a CA's test or staging endpoint (if there is one) after a failed attempt at getting a certificate to avoid hitting CA-enforced production rate limits. This could also be an ACME server you set up solely for the purpose of validating DNS configurations.
Let's Encrypt (others configurable)
External account binding
Optionally configure External Account Binding (EAB) to enable Caddy to work with CAs that require you to have a separate account with them.
Challenge types
Caddy supports all major ACME challenge types for Web PKI and can also be extended to support others.
HTTP-01
TLS-ALPN-01
DNS-01
Alternate challenge ports
While certain ACME challenges must use the standardized ports 80 and 443, Caddy supports listening for these on alternate ports if you are forwarding them through a router.
HTTP (default 80)
TLS-ALPN (default 443)
Smart challenge selection
Caddy learns what challenge types are most likely to succeed and tries those first. For example, if port 80 is blocked, it will learn to prefer the TLS-ALPN challenge which does not use port 80.
DNS challenge integrations
The DNS challenge is the only one that does not require the CA being able to access your server. Solve the DNS challenge with integrations for dozens of DNS providers via libdns. This list is incomplete;see the full list of DNS providers.
Optionally configure root certificates you trust when interacting with your CA of choice; this is helpful for internal PKI where trust is established without public CAs.
Preferred chains
When the CA offers multiple certificate chains, Caddy gives you the ability to customize which one to download and use.
Smallest
CommonName of root
CommonName of any
HTTP server
Caddy's HTTP server is one-of-a-kind: powerful, extensible, efficient, and modern.
HTTP versions
Caddy's HTTP server supports all major versions of HTTP and enables them by default (except H2C which is insecure, but available). You can customize exactly which versions you want to serve.
HTTP/1.1
HTTP/2
HTTP/2 over cleartext (H2C)
HTTP/3
HTTPS
Caddy's flagship feature is enabling HTTPS automatically and by default. You can control how it works or disable aspects: HTTP redirects, certificate management, certain hostnames, etc.
Automatic
Listen interfaces
Each HTTP server can bind to one or more sockets and network interfaces. For ports, you can specify specific host interface or all interfaces with just a port. All varieties of unix sockets are also supported.
TCP
UDP
Unix sockets
Listener wrappers
Listeners can be wrapped by modules that operate at the connection-accept level.
Redirect HTTP on HTTPS port
PROXY protocol
Tailscale
Timeouts
Setting timeouts is an important defensive measure for production environments, but must be tuned carefully to accommodate legitimate slow clients with large downloads or uploads.
Read timeout
Read HTTP header timeout
Write timeout
Idle timeout
TCP keepalive interval
Full duplex communication
Concurrent reading and writing of HTTP/1 is not supported by all clients, but can be enabled for certain clients and applications that require it.
Configurable for HTTP/1
Default for HTTP/2
Error handling
Caddy gives you full control over handling errors to give you clients the best/desired experience.
Custom error routes
TLS termination
Terminate TLS (formerly "SSL") with sensible defaults that you can customize to give you fine-grained control over TLS handshakes. You can assign policies to clients based on various factors such as ServerName (SNI) or remote IP.
TLS 1.2
TLS 1.3
Client authentication (TLS mutual auth; mTLS)
Client auth modes: request, require, verify if given, require and verify
Cipher suites
Curves
ALPN
Limit protocol versions
Default SNI
Fallback SNI
Cross-site security
Caddy often serves multiple sites on the same socket, so Caddy automatically enables protections to keep your sites safe if any of them have TLS client auth enabled.
Verification that TLS ServerName and HTTP Host header match
Access logs
Enable zero-allocation, structured access logs for the ultimate understanding of client requests and responses. Customize using Caddy's built-in logging configuration or the use of third-party modules.
More useful than Common Log Format (CLF)
Request headers (except sensitive fields)
Response headers
Remote IP
Latency
Observability
Your web server can be monitored using standards-compatible metrics.
Prometheus metrics, open telemetry
Request handling
The HTTP server handles requests using custom routes consisting of specific handlers in the order you define. A separate error route can be defined for custom error handling. You have a high degree of flexibility with HTTP handling. See below for available HTTP handler modules.
Composable routes (and separate error handling routes)
Request filters
Apply handlers to only certain requests using matchers, which classify requests based on various properties. Matchers are also used for filtering. They are extensible and pluggable, so there's no limit to how specific and custom your routes can be! Some matchers support regular expressions. All are quite fast. And matchers can be combined in sets so they can be joined with AND, OR, and NOT logic.
Host
Path
Method
Headers
Protocol
Remote IP
Arbitrary CEL expression
File (existence, size, modify date)
HTTP route variable
Logical NOT
Geolocation
Remote host
HTTP handlers
Handlers are modules that can be composed together to handle incoming requests precisely the way you want. Handler modules are, like the rest of Caddy, extensible and pluggable. It is not really feasible for us to list all the handlers here.
In practice, handlers are paired with matchers which filter or classify requests based on various properties such as their path, headers, query string, method, and more. This allows you to selectively apply any and all of these handlers to certain requests.
ACME server
Right out of the box, Caddy ships with a production-ready ACME server, perfect for your internal PKI. Automate mTLS certificates inside your infrastructure with ease. Powered by Smallstep libraries.
Authelia
Secure routes with authentication using Authelia.
Authentication
Authenticate users with an extensible authentication module. Extended by auth providers, this handler returns an error if the user cannot be authenticated by any configured providers. HTTP basicauth is included standard, and unlike other servers, passwords are hashed when setting up basicauth (since it's essentially a password database), enhancing security.
HTTP Basic authentication
JWT
Discord
Forms
SAML
Advanced auth
With a full suite of authentication and authorization features, the caddy-security module provides a variety of robust auth solutions.
Form-based
Local
Basic
LDAP
OpenID Connect
OAuth 2
SAML
Cache
Easily enable caching to serve more clients and increase performance. This cache module is compliant with RFC 7234 and supports tag-based cache purge, distributed and local storage, key generation tweaking, and more. Multiple backends are supported!
Badger
Etcd
NutsDB
Olric
Redis
Encode
Compress, encode, or otherwise transform HTTP responses on-the-fly with pluggable encoding modules. Compressing responses is as easy as a single line of configuration, and encodings won't be applied to responses that are already in a compressed format or are too small to be worthwhile.
Gzip
Zstandard (zstd)
Brotli
File server
A powerful, flexible, and efficient static file server that is described in detail below.
Go package vanity paths
A simple handler that implements vanity import paths for Go packages.
gRPC-Web bridging
Bridge/convert gRPC-Web requests to gRPC for your backend app.
Header manipulation
Modify HTTP request and response headers. Adding, setting, deleting, and replacing substrings in header fields is fast, but regular expressions are also supported for advanced use. Response header manipulations can be deferred until the very end when the response starts to be written, and can even be made conditional on response status code or header values.
Add
Set (overwrite)
Delete
Substring replace
Image filtering
Perform adjustments on images on-the-fly.
Crop
Fit
Flip
Resize
Rotate
Sharpen
Map
Assign variable/placeholder values based on input values; similar to a lookup table.
Mercure
Make your Caddy instance a Mercure hub: an open, easy, fast, reliable and battery-efficient solution for real-time communications.
Metrics
Expose a /metrics endpoint for use with Prometheus-compatible systems and other monitoring tools.
HTTP/2 server push
Proactively push resources to clients before they request it when HTTP/2 is used. (May be deprecated by browsers, but Caddy still has a valid implementation that is useful in certain applications.)
Rate limiting
Advanced, enterprise-grade rate limiter implemented using a ring buffer and sliding window algorithm that scales massively based on zone keys. Configure a cluster of Caddy instances with the same storage to distribute rate limiting across your fleet. No memory bound required like with other enterprise servers.
Local or distributed
Multiple zones
Buffer pooling
Only 1 goroutine
Configurable O(Kn) memory management
State persisted through reloads
Sets Retry-After header
Optional jitter
Highly programmable
Request body controls
Restrict the size of the request body by rejecting requests that are too large.
Reverse proxy
Caddy has a world-class reverse proxy, described in detail in a section below.
Rewrite requests
Make internal changes to requests before continuing to process them. This is useful to accept requests that need to be changed to conform to an expectation later on. Various aspects of the request can be changed such as method and URI.
Method
URI (path, query string)
Strip path prefix or suffix
Regular expression support
Intelligent URL-encoding and forward-slash handling
Static responses
Hard-code a static response into your config, with the ability to set the status code, header fields, and body. (This is often used to respond with HTTP redirects.) The connection may then be gracefully closed, or forcefully aborted if needed.
Subrouting
Group handlers into a "subroute" to treat several handlers as one, making certain logic easier to reason about.
Templates
Responses can be evaluated as templates, which give you the ability to turn proxied or static content into rich, dynamic content with variables, if statements, markdown rendering (with front matter support), and more.
Tracing
Support for distributed tracing using OpenTelemetry.
Variables
Read and write variables that can be used internally as you process requests.
WebDAV
Become a WebDAV server with one or two lines of config. Compatible with most WebDAV clients.
Reverse proxy
Caddy has the most flexible general-purpose reverse proxy in the world, featuring advanced request and response handling, dynamic routing, health checking, load balancing, circuit breaking, and more.
What makes Caddy's proxy unique is its design. Only the client-facing side of the proxy needs to be HTTP; the transport underlying the roundtrip with the backend can be fulfilled with any protocol!
Moreover, our proxy can be programmed with highly dynamic upstreams. That is, the available upstreams can change during in-flight requests! If no backends are available, Caddy can hold onto the request until one is.
High-level proxy features
Transports
Transports are how Caddy gets the response from the backend. Caddy's proxy can be a front for protocols other than HTTP by using alternate transport modules. This allows Caddy to generate HTTP responses from backends that don't even speak HTTP!
HTTP
FastCGI
NTLM
Load balancing
Selecting upstreams is a crucial function of any modern reverse proxy. Caddy has a variety of built-in load balancing policies to choose from to suit any production services. Some policies are extremely fast and lightweight; others provide upstream affinity based on properties of the client or request; others strive for even distribution by counting connections or using randomness and weights.
Random
Random Choose-N
Least connections
Round robin
Weighted round robin
First available
Remote IP hash
Client IP hash
URI hash
Query hash
Header hash
Cookie hash
Circuit breaking
A circuit breaker module can temporarily mark a backend as down before it actually goes down, to keep it up.
Latency-based
Health checking
Health checks detect when upstreams are unavailable. Passive health checks infer status from actual requests. Active health checks work in the background, out-of-band of client requests.
Active
Passive
Observability
The admin API exposes an endpoint to retrieve the traffic count and health status of the proxy upstreams.
Upstream sources
Caddy can get the list of upstreams in various ways. The most common is to write them into the configuration (static). Other ways are dynamic, by which a list of upstreams are returned for each request (these utilize configurable caching to enhance performance).
Static
Dynamic: A records
Dynamic: SRV records
Dynamic: Multiple sources combined
Retries
Requests can be retried until a backend is available to successfully handle the request. During this time, the list of upstreams may even be updated while the request is still pending!
Streaming
Responses can be streamed directly to the client, or for better wire performance, buffered slightly and flushed periodically.
Trusted proxies
In order to use proxy-related headers like X-Forwarded-For, you can specify a list of IP ranges of proxies you trust. By default Caddy doesn't trust the clients.
Header manipulation
Headers can be modified in the request going up to the backend and the response coming back down from the backend. This is similar to the general HTTP server's header handler, but this is applied while proxying.
Add
Set (overwrite)
Delete
Substring replace
Buffering
The proxy can optionally read the entire body before flushing it. This uses more memory but can be required by some backend applications or clients in some cases.
Requests
Responses
Request rewriting
Rewriting is a different concern from proxying and is normally handled separately, but sometimes you need to rewrite requests using information from the proxy like the chosen upstream. Caddy's proxy lets you do this.
Response interception
By default, Caddy's proxy simply writes responses to the client. However, you can intercept the upstream's response and handle it in other ways. This includes matching only certain responses and invoking a custom handler chain you specify.
Active health checks
Active health checks assume a backend is down by default until that is confirmed otherwise by a health check.
HTTP request parameters
Active health checks are performed against an HTTP endpoint on the upstream. You can customize the parameters for these HTTP requests to work for you.
Path & query string
Port
Headers
Timing
You can customize the interval at which active health checks are performed.
Success criteria
Each active health check can be customized with a set of criteria to determine healthy or unhealthy status.
Response timeout
HTTP status code
Regular expression match on body
Failure safety
Backends that are experiencing bugs and difficulties may sometimes respond with unexpectedly large response bodies. Caddy lets you limit this to preserve proxy resources.
Limit response size
Passive health checks
Passive health checks assume a backend is up by default until failure criteria are met in the course of proxying requests.
Failure criteria
All passive health checks count connection failures. In addition, you can set more criteria needed to deem a backend as healthy during a request.
Concurrent request limit exceeded
HTTP Status
Latency
Failure memory
You can customize how long to remember failures and how many failures need to be in memory to consider a backend to be down.
HTTP transport
This is the default transport module. It crafts a proxied HTTP request to obtain an HTTP response from the backend.
DNS resolvers
The system resolvers are used by default, but you can specify custom DNS resolvers per proxy handler.
TLS
Caddy can be configured to support TLS (formerly known as SSL) to the upstream.
Custom root CA pool
Client authentication to backend
Custom handshake timeout
Server Name Indicator (SNI)
Renegotiation level
Exempt certain ports from TLS
Connection pooling
Connections to backends are pooled for maximum efficiency and minimal latency.
HTTP Keep-Alive
Custom probe interval
Maximum idle connections (total and per-host)
Idle connection timeout
Compression
Caddy can compress requests for the roundtrip with the backend.
Gzip
Connection limit
You can limit the number of connections per host.
PROXY Protocol
The PROXY Protocol v1 and v2 are both supported when connecting to upstreams.
Timeouts
Various timeouts can be configured; some have sensible default values.
Connection (dial)
RFC 6555 fallback
Reading response headers
Expect continue
Read
Write
Custom buffer sizes
Tune the size of read/write buffers if you find that your application performs better with certain settings.
Read buffers
Write buffers
HTTP versions
Caddy's proxy supports multiple HTTP versions with the backend. By default, HTTP/1.1 and HTTP/2 are supported.
HTTP/1.1
HTTP/2
H2C (HTTP/2 over cleartext)
FastCGI transport
FastCGI is typically used to serve PHP applications via php-fpm. FastCGI responders may require additional information about the script being run such as script name, path relative to root, etc., and Caddy's FastCGI transport takes care of all of that and makes it configurable.
Highly efficient
Caddy's FastCGI client implementation has been optimized to rival the performance of memory-unsafe clients written in C, sometimes even surpassing their performance.
Path splitting
The path can be split, usually at the extension, to compute the proper PATH_INFO variable.
Resolve root symlink
Optionally require paths declared to symlinks to be updated if the symlink changes without php-fpm being restarted.
Environment variables
Read from the parent environment, and also set custom environment variables for your CGI script.
Timeouts
Set timeouts to conserve resources.
Dial (connect)
Read
Write
Capture stderr
Caddy can capture the output to stderr from the upstream and log them for visibility.
Static file server
Caddy's file server is the premier way of serving static files for your website.
It's simple: specify a root directory from which to serve the files, then each request path is automatically appended to the root to get the full path of the file to serve.
Kernel acceleration
Caddy bypasses user-space buffers whenever possible to speed up file downloads by a significant factor.
sendfile
Virtual file systems
By default, Caddy serves files from a directory you specify on the local disk, but this file access is pluggable and can be replaced by any virtualized file system modules. This allows you to serve static files from any file store such as databases, cloud storage, or even assets embedded directly in the web server binary!
Local disk
Embedded assets
Amazon AWS S3
Precompressed files
If your deployment pipeline compresses site resources, Caddy can automatically detect them and serve them in their "precompressed" encoding for higher efficiency and greater throughput.
Gzip
Brotli
Zstandard
Hide files and folders
Increase your security posture by proactively hiding potentially-sensitive files and folders that do or could exist in your site root. You can specify individual file/folder paths, filenames regardless of their path, or glob matches to hide files/folders with a particular pattern.
Exact paths, filenames, globular matching
Index filenames
Index files are files that are served if a directory is requested by the client. The filenames of index files to look for are customizable. Directory browsing can optionally be enabled if an index file is not found in a requested directory.
index.html, index.txt (customizable)
Conditional requests
Etag, Last-Modified, and related headers are supported.
Etag
Last-Modified
If-Match
If-None-Match
If-Modified-Since
If-Unmodified-Since
If-Range
Range requests
Common for streaming large files and resuming downloads, clients requesting certain ranges of files will not be disappointed or surprised. Caddy properly handles HTTP requests with Range headers.
Canonical paths
In general, there are multiple URIs for a single file or directory. For example: /, /index.html, and /index.html/ represent the same resource. Caddy uses HTTP redirects to enforce path canonicalization (removing trailing slashes from files, and adding them for directories).
Pass-thru mode
Sometimes you only want to serve a file if it exists, otherwise continue with the next handler in the chain, rather than returning an error to the client.
File browser
Caddy's file server comes alive through its modern file browser that looks attractive on mobile and desktop. It has more features and utility than any other standard HTTP file server!
Folder listings
Show the list of files in a folder when no index file (below) exists in that folder.
Exact paths, filenames, globular matching
Day and night themes
The color scheme automatically adjusts to match the system theme, whether it be light or dark, to avoid blinding you or being hard to read.
Light mode
Dark mode
Sort by columns
Quickly distill information about each directory and find items faster with sticky column sorting.
File/directory
Name
Size
Date modified
Filter
Every page load automatically focuses the cursor on a search box, so you can start typing a filename and filter large listings instantly.
Layout
Files can be shown in different layouts depending on how you want to view the listing. For example, the grid view is great for galleries.
List
Grid
Responsive design
The page width fluidly adjusts to accommodate screens of all sizes. Links are sufficiently sized to be easily tappable on touchscreens while still being information-dense enough to be useful.
JSON API
Requests with an Accept-Encoding: application/json header will be replied to with a JSON payload for programmatic or scripted access to your file listing.
Customizable listing template
If the default template isn't a good fit or you want to spice things up, customize the browse template to look and act any way you want!
File size visualization
File sizes are indicated by the length of the bar behind them, making it quick and easy to find outlier large and small files or to compare relative sizes at a glance.
File type icons
The file server recognizes dozens of common file types and shows associated icons to make identification easier when scanning the page.
Caddy is a living project with a TON of features. This page is not yet a comprehensive list of all the features and benefits provided by Caddy because there's so many to mention. We welcome contributions on GitHub!
