Hard coding (also hard-coding or hardcoding) is the software development practice of embedding data directly into the source code of a program or other executable object, as opposed to obtaining the data from external sources or generating it at runtime.

Hard-coded data typically can be modified only by editing the source code and recompiling the executable, although it can be changed in memory or on disk using a debugger or hex editor.

Data that is hard-coded is best suited for unchanging pieces of information, such as physical constants, version numbers, and static text elements.

Soft-coded data, on the other hand, encodes arbitrary information through user input, text files, INI files, HTTP server responses, configuration files, preprocessor macros, external constants, databases, command-line arguments, and is determined at runtime.

Hard coding requires the program's source code to be changed any time the input data or desired format changes, when it might be more convenient to the end user to change the detail by some means outside the program.

Hard coding is often required, but can also be considered an anti-pattern. Programmers may not have a dynamic user interface solution for the end user worked out but must still deliver the feature or release the program. This is usually temporary but does resolve, in a short-term sense, the pressure to deliver the code. Later, soft coding is done to allow a user to pass on parameters that give the end user a way to modify the results or outcome.

The term "hard-coded" was initially used as an analogy to hardwiring circuits, and was meant to convey the inflexibility that results from its usage within software design and implementation. In the context of run-time extensible collaborative development environments such as MUDs, hard coding also refers to developing the core engine of the system responsible for low-level tasks and executing scripts, as opposed to soft coding which is developing the high-level scripts that get interpreted by the system at runtime, with values from external sources, such as text files, INI files, preprocessor macros, external constants, databases, command-line arguments, HTTP server responses, configuration files, and user input. In this case, the term is not pejorative and refers to general development, rather than specifically embedding output data.

Hard coding credentials is a popular way of creating a backdoor. Hard coded credentials are usually not visible in configuration files or the output of account-enumeration commands and cannot be easily changed or bypassed by users. If discovered, a user might be able to disable such a backdoor by modifying and rebuilding the program from its source code (if source is publicly available), decompiling, or reverse-engineering software, directly editing the program's binary code, or instituting an integrity check (such as digital signatures, anti-tamper, and anti-cheat) to prevent the unexpected access, but such actions are often prohibited by an end-user license agreement.