Nim Standard Library

"The good thing about reinventing the wheel is that you can get a round one."

Though the Nim Standard Library is still evolving, it is already quite usable. It is divided into pure libraries, impure libraries and wrappers.

Pure libraries do not depend on any external *.dll or lib*.so binary while impure libraries do. A wrapper is an impure library that is a very low-level interface to a C library.

Read this document for a quick overview of the API design.

The bottom of this page includes a list of 3rd party packages created by the Nim community. These packages are a useful addition to the modules in the standard library.

Pure libraries


  • system Basic procs and operators that every program needs. It also provides IO facilities for reading and writing text and binary files. It is imported implicitly by the compiler. Do not import it directly. It relies on compiler magic to work.
  • threads Nim thread support. Note: This is part of the system module. Do not import it explicitly.
  • channels Nim message passing support for threads. Note: This is part of the system module. Do not import it explicitly.
  • locks Locks and condition variables for Nim.
  • rlocks Reentrant locks for Nim.
  • macros Contains the AST API and documentation of Nim for writing macros.
  • typeinfo Provides (unsafe) access to Nim's run time type information.
  • typetraits This module defines compile-time reflection procs for working with types.
  • threadpool Implements Nim's spawn.
  • cpuinfo This module implements procs to determine the number of CPUs / cores.
  • lenientops Provides binary operators for mixed integer/float expressions for convenience.

Collections and algorithms

  • algorithm Implements some common generic algorithms like sort or binary search.
  • tables Nim hash table support. Contains tables, ordered tables and count tables.
  • sets Nim hash and bit set support.
  • lists Nim linked list support. Contains singly and doubly linked lists and circular lists ("rings").
  • deques Implementation of a double-ended queue. The underlying implementation uses a seq.
  • intsets Efficient implementation of a set of ints as a sparse bit set.
  • critbits This module implements a crit bit tree which is an efficient container for a sorted set of strings, or for a sorted mapping of strings.
  • sequtils This module implements operations for the built-in seq type which were inspired by functional programming languages.
  • sharedtables Nim shared hash table support. Contains shared tables.
  • sharedlist Nim shared linked list support. Contains shared singly linked list.

String handling

  • strutils This module contains common string handling operations like changing case of a string, splitting a string into substrings, searching for substrings, replacing substrings.
  • strformat Macro based standard string interpolation / formatting. Inpired by Python's ```f``-strings.
  • strmisc This module contains uncommon string handling operations that do not fit with the commonly used operations in strutils.
  • parseutils This module contains helpers for parsing tokens, numbers, identifiers, etc.
  • strscans This module contains a scanf macro for convenient parsing of mini languages.
  • strtabs The strtabs module implements an efficient hash table that is a mapping from strings to strings. Supports a case-sensitive, case-insensitive and style-insensitive mode. An efficient string substitution operator % for the string table is also provided.
  • unicode This module provides support to handle the Unicode UTF-8 encoding.
  • encodings Converts between different character encodings. On UNIX, this uses the iconv library, on Windows the Windows API.
  • pegs This module contains procedures and operators for handling PEGs.
  • ropes This module contains support for a rope data type. Ropes can represent very long strings efficiently; especially concatenation is done in O(1) instead of O(n).
  • matchers This module contains various string matchers for email addresses, etc.
  • subexes This module implements advanced string substitution operations.

Generic Operating System Services

  • os Basic operating system facilities like retrieving environment variables, reading command line arguments, working with directories, running shell commands, etc.
  • osproc Module for process communication beyond os.execShellCmd.
  • times The times module contains basic support for working with time.
  • dynlib This module implements the ability to access symbols from shared libraries.
  • streams This module provides a stream interface and two implementations thereof: the FileStream and the StringStream which implement the stream interface for Nim file objects (File) and strings. Other modules may provide other implementations for this standard stream interface.
  • marshal Contains procs for serialization and deseralization of arbitrary Nim data structures.
  • terminal This module contains a few procedures to control the terminal (also called console). The implementation simply uses ANSI escape sequences and does not depend on any other module.
  • memfiles This module provides support for memory mapped files (Posix's mmap) on the different operating systems.
  • asyncfile This module implements asynchronous file reading and writing using asyncdispatch.
  • distros This module implements the basics for OS distribution ("distro") detection and the OS's native package manager. Its primary purpose is to produce output for Nimble packages, but it also contains the widely used Distribution enum that is useful for writing platform specific code.

Math libraries

  • math Mathematical operations like cosine, square root.
  • complex This module implements complex numbers and their mathematical operations.
  • rationals This module implements rational numbers and their mathematical operations.
  • fenv Floating-point environment. Handling of floating-point rounding and exceptions (overflow, zero-devide, etc.).
  • mersenne Mersenne twister random number generator.
  • random Fast and tiny random number generator.
  • stats Statistical analysis

Internet Protocols and Support

  • cgi This module implements helpers for CGI applications.
  • scgi This module implements helpers for SCGI applications.
  • browsers This module implements procs for opening URLs with the user's default browser.
  • httpclient This module implements a simple HTTP client which supports both synchronous and asynchronous retrieval of web pages.
  • smtp This module implement a simple SMTP client.
  • cookies This module contains helper procs for parsing and generating cookies.
  • mimetypes This module implements a mimetypes database.
  • uri This module provides functions for working with URIs.
  • asyncdispatch This module implements an asynchronous dispatcher for IO operations.
  • asyncnet This module implements asynchronous sockets based on the asyncdispatch module.
  • asynchttpserver This module implements an asynchronous HTTP server using the asyncnet module.
  • asyncftpclient This module implements an asynchronous FTP client using the asyncnet module.
  • net This module implements a high-level sockets API. It will replace the sockets module in the future.
  • nativesockets This module implements a low-level sockets API.
  • selectors This module implements a selector API with backends specific to each OS. Currently epoll on Linux and select on other operating systems.


  • parseopt The parseopt module implements a command line option parser.
  • parsecfg The parsecfg module implements a high performance configuration file parser. The configuration file's syntax is similar to the Windows .ini format, but much more powerful, as it is not a line based parser. String literals, raw string literals and triple quote string literals are supported as in the Nim programming language.
  • parsexml The parsexml module implements a simple high performance XML/HTML parser. The only encoding that is supported is UTF-8. The parser has been designed to be somewhat error correcting, so that even some "wild HTML" found on the Web can be parsed with it.
  • parsecsv The parsecsv module implements a simple high performance CSV parser.
  • parsesql The parsesql module implements a simple high performance SQL parser.
  • json High performance JSON parser.
  • lexbase This is a low level module that implements an extremely efficient buffering scheme for lexers and parsers. This is used by the diverse parsing modules.
  • highlite Source highlighter for programming or markup languages. Currently only few languages are supported, other languages may be added. The interface supports one language nested in another.
  • rst This module implements a reStructuredText parser. A large subset is implemented. Some features of the markdown wiki syntax are also supported.
  • rstast This module implements an AST for the reStructuredText parser.
  • rstgen This module implements a generator of HTML/Latex from reStructuredText.
  • sexp High performance sexp parser and generator, mainly for communication with emacs.

XML Processing

  • xmldom This module implements the XML DOM Level 2.
  • xmldomparser This module parses an XML Document into a XML DOM Document representation.
  • xmltree A simple XML tree. More efficient and simpler than the DOM. It also contains a macro for XML/HTML code generation.
  • xmlparser This module parses an XML document and creates its XML tree representation.
  • htmlparser This module parses an HTML document and creates its XML tree representation.
  • htmlgen This module implements a simple XML and HTML code generator. Each commonly used HTML tag has a corresponding macro that generates a string with its HTML representation.

Cryptography and Hashing

  • hashes This module implements efficient computations of hash values for diverse Nim types.
  • md5 This module implements the MD5 checksum algorithm.
  • base64 This module implements a base64 encoder and decoder.
  • sha1 This module implements a sha1 encoder and decoder.

Multimedia support

  • colors This module implements color handling for Nim. It is used by the graphics module.


  • oids An OID is a global ID that consists of a timestamp, a unique counter and a random value. This combination should suffice to produce a globally distributed unique ID. This implementation was extracted from the Mongodb interface and it thus binary compatible with a Mongo OID.
  • endians This module contains helpers that deal with different byte orders.
  • logging This module implements a simple logger.
  • options Types which encapsulate an optional value.
  • sugar This module implements nice syntactic sugar based on Nim's macro system.
  • coro This module implements experimental coroutines in Nim.
  • unittest Implements a Unit testing DSL.
  • segfaults Turns access violations or segfaults into a NilAccessError exception.

Modules for JS backend

  • dom Declaration of the Document Object Model for the JS backend.
  • jsffi Types and macros for easier interaction with JavaScript.
  • asyncjs Types and macros for writing asynchronous procedures in JavaScript.
  • jscore Wrapper of core JavaScript functions. For most purposes you should be using the math, json, and times stdlib modules instead of this module.

Impure libraries

Regular expressions

  • re This module contains procedures and operators for handling regular expressions. The current implementation uses PCRE.

Database support

  • db_postgres A higher level PostgreSQL database wrapper. The same interface is implemented for other databases too.
  • db_mysql A higher level MySQL database wrapper. The same interface is implemented for other databases too.
  • db_sqlite A higher level SQLite database wrapper. The same interface is implemented for other databases too.


  • ssl This module provides an easy to use sockets-style Nim interface to the OpenSSL library.


The generated HTML for some of these wrappers is so huge that it is not contained in the distribution. You can then find them on the website.

Windows specific

  • winlean Contains a wrapper for a small subset of the Win32 API.

UNIX specific

  • posix Contains a wrapper for the POSIX standard.

Regular expressions

  • pcre Wrapper for the PCRE library.

GUI libraries

  • iup Wrapper of the IUP GUI library.

Database support

  • postgres Contains a wrapper for the PostgreSQL API.
  • mysql Contains a wrapper for the mySQL API.
  • sqlite3 Contains a wrapper for SQLite 3 API.
  • odbcsql interface to the ODBC driver.

Network Programming and Internet Protocols


Nimble is a package manager for the Nim programming language. For instructions on how to install Nimble packages see its README.

To see a list of Nimble's packages, check out https://nimble.directory/ or the packages repos on GitHub.

© 2006–2018 Andreas Rumpf
Licensed under the MIT License.