hh_client(1) Interface to Hack language typechecker




hh_client(1) is an interface to a static analysis tool which is what enforces most of the Hack language's type system. Code must pass validation of this tool in order to be considered valid code in the Hack language.

There are several possible MODEs for hh_client(1) (see below). By default, it will invoke the check mode, with the current directory as DIRECTORY. These are reasonable defaults, meaning that most users can simply invoke the command as


with no arguments to get a list of type errors across the entire project.

All of the MODEs accept a DIRECTORY as an optional final argument. This denotes the project upon which to operate. hh_client(1) walks up the filesystem from the DIRECTORY until it finds a file called .hhconfig and then operates on the body of Hack language code rooted in this directory. If no DIRECTORY is specified, it uses the current directory by default. This means you may run hh_client(1) in any subdirectory of your project and get type errors for the whole project without ever specifying a DIRECTORY explicitly.

hh_client(1) implements very little logic itself, but rather serves as an interface to the hh_server(1) daemon. The server will automatically be started and restarted as needed.



The default MODE if none is specified. With no OPTIONS specified, it prints a list of type errors on standard output, or prints "No errors!" if there were none.

Many OPTIONS affect the output of check mode, sometimes causing it to do completely different things. (Those can be considered "sub-modes" of check mode.) Many of these options are undergoing considerable revision and so are not documented here; read the source for a full list.

Widely-useful OPTIONS for check mode include:

--color FILE
Sub-mode which prints out information on what parts of FILE are actually typechecked and which are not. Due to Hack's partial mode and PHP interoperability, the type system may not know the types of parts of a program. In this case, it trusts the programmer and carries on. The --color mode prints out a file with ANSI terminal colors, where green code is actually fully checked, and red code cannot be fully checked due to such missing type information.

Prints information about hh_client(1) and its command line options, and then exits. Many of the options described there are experimental, especially if they are not described in this man page.

--from EDITOR
Prints output in the format expected by a specific editor. Valid values of EDITOR are emacs and vim. For usage by other tools, try --json instead.

Prints output in a JSON format intended for machine consumption, instead of the output intended for human consumption that is output by default.

--retries NUM
If the typechecker daemon is busy, try NUM times to connect to it before giving up. Set NUM to 0 to disable retries if the server is not immediately available.

Prints human-readable type error information to standard out and then exits. The default sub-mode of check if none is specified. This output is not intended for usage by tools, but only for human consumption. For output intended for tool usage, see the --json and/or --from options.

Prints the current client version, including build ID and build date, and then exits.

Autocompletes text on STDIN where the cursor is replaced with AUTO332. Returns a newline-separated list.

--search STRING
Fuzzy search symbol definitions for STRING. Returns a newline-separated list.


Explicitly starts the hh_server(1) daemon if it is not already running. This is not normally necessary, since check mode will start it as needed if it is not running.


Explicitly stops the hh_server(1) daemon if it is running. This is not normally necessary, since the daemon will exit if it has not been used for an extended period of time.


Explicitly stops and then starts again the hh_server(1) daemon. Fails if the daemon is not currently running. Restarting the daemon is not normally necessary, since it updates its state in the background, and hh_client(1) will restart it automatically if the typechecker binaries have been updated.


For check mode in the --status sub-mode, hh_client(1) returns 0 if there are no type errors, and non-zero otherwise.

Exit statuses for any other invocations are currently undefined and subject to change.


Used in combination with the path to the project root in order to locate the socket for communicating with the running hh_server(1) daemon. Normally set by your login environment, but may be unset in some nonstandard setups.


When determining where the project root is in order to figure out what files to actually typecheck, hh_client(1) walks up the directory tree from the specified DIRECTORY until it finds this file. The set of files recursively included in the directory with the .hhconfig file is the set of files typechecked.

The client looks inside this directory for sockets to communicate with the hh_server(1) daemon. The sockets are named based on a hash of the absolute path of the project root.


The Hack language is part of the HHVM project. Known bugs can be found at that tracker, and new ones should be reported there as well: https://github.com/facebook/hhvm/issues