ALI File

What are ALI files and how to open them

Are you having problems opening an ALI file or are you simply curious about its contents? We're here to explain the properties of these files and provide you with software that can open or handle your ALI files.

What is an ALI file?

ALI files have multiple uses, and GNAT Ada Library Information is one of them. Read more about the other uses further down the page.

GNAT Ada Library Information

GNAT Ada Library Information files store metadata about compiled Ada units. These text files are produced by the GNAT compiler when you compile an Ada source unit. Alongside the actual object file (often with a .o extension), a corresponding file is created which records everything GNAT needs later to check consistency, compute build dependencies, and control linking and elaboration order.

The file holds version data for both the GNAT compiler itself and the standard library representation as seen by the unit. It includes information about compilation settings like main program attributes, character encoding, command-line arguments, configuration pragmas, and exception models. It also notes restrictions like purity or pragma categorization, what other units are "with"ed (including Elaborate or Elaborate_All), any Linker_Options pragmas, and whether Body_Version or Version attributes were used. Most importantly, there is a dependency list: files that the unit depends on, each with a timestamp and checksum so GNAT knows when recompilation is required. Cross-reference information about all entities referenced in the unit is also present, allowing tools to provide source navigation or dependency graphs.

These files are used by various GNAT tools: the binder references them to ensure all compiled units are consistent before linking; build tools like gnatmake use them to decide what must be recompiled; library infrastructure uses them to establish the order in which Ada units are elaborated at run time. The format spec is implemented in GNAT's source, in units such as Lib.Writ, which produce and read these files.

Text files begin with specific header lines identifying the GNAT library output version ("V …") and the Standard library version ("S …"). Other lines start with single characters or keywords indicating types of information: for example, "M" for main program kind and priority, "F" for flags, lists of "with"ed units, etc. Every ALI file begins with an ASCII signature "V\"GNATLibv" at the start, at offset zero.

How to open ALI files

Important: Different programs may use files with the ALI file extension for different purposes, so unless you are sure which format your ALI file is, you may need to try a few different programs.

While we have not verified the apps ourselves yet, our users have suggested two different ALI openers which you will find listed below.

Last updated: August 17, 2026

All known file formats using extension .ALI

While GNAT Ada Library Information is a popular type of ALI-file, we know of 2 different uses of the .ALI file extension. Different software may use files with the same extension for different types of data.

RoboHelp Alias File

A RoboHelp Alias File (extension .ALI) is a plain-text file used by Adobe RoboHelp to map symbolic alias identifiers to specific help topic files in a help project. Authors use alias files as part of Context-Sensitive Help: when a user presses F1 or a Help button inside an application, the application supplies an alias or ID, and RoboHelp finds the matching help topic via the alias file. The alias file thus links the alias name to the filename of the HTML (or equivalent) topic within the RoboHelp project.

In practice, ALI files are generated or updated within RoboHelp whenever authors configure Map Files under the Context Sensitive Help settings. An alias file works together with a Map (header) file (.HH or .HM) which defines numeric or symbolic IDs and their combinations with alias names. Developers may use those IDs in application code, while the ALI file lets the help system locate the actual topic.

Aliases are stored in ALI files as XML-style or simple mapping entries, each specifying an alias name and the relative link to an HTML topic. For example, an entry might look like or Login=Logon.htm. ALI files are viewable and editable with any text editor.

ALI opener for Windows

We have identified one ALI opener that is compatible with this specific type of ALI file.

Various apps that use files with this extension

These apps are known to open certain types of ALI files. Remember, different programs may use ALI files for different purposes, so you may need to try out a few of them to be able to open your specific file.

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