An “.AM” file may correspond to multiple unrelated file types because extensions aren’t controlled globally and developers reuse them freely, meaning .am files may be plain-text build configs, scientific/3D-visualization data sets, or older multimedia project files, while Windows’ file associations can further blur things by choosing an opener without checking the real data, and the most common developer-facing version is “Makefile.am,” an Automake template listing variables such as bin_PROGRAMS which get transformed into Makefile.in and eventually a Makefile for `make` to build the project.Other uses can be found, such as Amira/Avizo AmiraMesh scientific-visualization data with readable headers plus binary segments, or Anark Media files from older multimedia systems that look almost entirely binary in plain text, and the quickest way to figure out what your .am file is involves checking where it came from and viewing its contents—readable build instructions typically mean Automake, scientific-style headers or mesh/data cues point to AmiraMesh, and unreadable characters imply a binary media type—while a real byte inspector like the content-based “file” program provides dependable identification.The reason the `file` command proves so accurate is that it doesn’t rely on the extension at all but instead inspects the bytes inside the file, comparing them to known patterns or *magic numbers* along with structural hints, since many formats start with distinctive headers or predictable sequences, and even when no clear signature exists, `file` can still judge whether the content resembles text, JSON/XML, scripts, compressed data, executables, or generic binary blobs, making it particularly helpful for ambiguous extensions like `.am` because it reports what the data actually looks like rather than what Windows thinks should open it.In practice, if your `.am` belongs to Automake, `file` tends to mark it as readable text, sometimes categorizing it as a makefile, while scientific or media `.am` files often return as data, binary, or a detected format if signatures align, and this also catches mislabeled files—such as an `.am` that is actually ZIP/gzip—something that happens often when names are changed, with Linux/macOS users calling `file yourfile.am` and Windows users using tools like Git Bash, WSL, Cygwin, or GnuWin32, all producing output that hints at the file’s true role and whether reading it as text is appropriate.To understand what your .AM file is, the simplest and fastest tool is context combined with a short content inspection, because “.am” is reused across different workflows, meaning that a `Makefile.am` inside a directory containing code-related files such as `configure.ac` or `aclocal.m4` almost certainly comes from GNU Automake and defines build rules, while files like `model.am` or `dataset.am` originating from scientific, medical, or 3D visualization projects typically point to AmiraMesh, which begins with a readable metadata header and includes a mixed-format data section.If AM file extension was generated in an older presentation pipeline and doesn’t resemble source code or scientific descriptors, it could be an Anark Media file, which usually shows binary gibberish in Notepad, and that test helps differentiate: human-readable build lines indicate Automake, structured technical headers imply scientific visualization, and heavy gibberish marks a binary media format, with size offering only a loose clue, making its origin and initial lines the most trustworthy guide.