Application programming interface

In computer programming, an application programming interface (API) is a set of subroutine definitions, communication protocols, and tools for building software. In general terms, it is a set of clearly defined methods of communication among various components. A good API makes it easier to develop a computer program by providing all the building blocks, which are then put together by the programmer.

An API may be for a web-based system, operating system, database system, computer hardware, or software library.

An API specification can take many forms, but often includes specifications for routines, data structures, object classes, variables, or remote calls. POSIX, Windows API and ASPI are examples of different forms of APIs. Documentation for the API usually is provided to facilitate usage and implementation.


In building applications, an API simplifies programming by abstracting the underlying implementation and only exposing objects or actions the developer needs. While a graphical interface for an email client might provide a user with a button that performs all the steps for fetching and highlighting new emails, an API for file input/output might give the developer a function that copies a file from one location to another without requiring that the developer understand the file system operations occurring behind the scenes.[1]


The term API seems to appear for the first time in the article of Ira W. Cotton, Data structures and techniques for remote computer graphics, published in 1968.


Libraries and frameworks

An API usually is related to a software library. The API describes and prescribes the "expected behavior" (a specification) while the library is an "actual implementation" of this set of rules.

A single API can have multiple implementations (or none, being abstract) in the form of different libraries that share the same programming interface.

The separation of the API from its implementation can allow programs written in one language to use a library written in another. For example, because Scala and Java compile to compatible bytecode, Scala developers can take advantage of any Java API.[2]

API use can vary depending on the type of programming language involved. An API for a procedural language such as Lua could consist primarily of basic routines to execute code, manipulate data or handle errors while an API for an object-oriented language, such as Java, would provide a specification of classes and its class methods.[3][4]

Language bindings are also APIs. By mapping the features and capabilities of one language to an interface implemented in another language, a language binding allows a library or service written in one language to be used when developing in another language.[5] Tools such as SWIG and F2PY, a Fortran-to-Python interface generator, facilitate the creation of such interfaces.[6]

An API can also be related to a software framework: a framework can be based on several libraries implementing several APIs, but unlike the normal use of an API, the access to the behavior built into the framework is mediated by extending its content with new classes plugged into the framework itself.

Moreover, the overall program flow of control can be out of the control of the caller and in the hands of the framework by inversion of control or a similar mechanism.[7][8]

Operating systems

An API can specify the interface between an application and the operating system.[9] POSIX, for example, specifies a set of common APIs that aim to enable an application written for a POSIX conformant operating system to be compiled for another POSIX conformant operating system.

Linux and Berkeley Software Distribution are examples of operating systems that implement the POSIX APIs.[10]

Microsoft has shown a strong commitment to a backward-compatible API, particularly within its Windows API (Win32) library, so older applications may run on newer versions of Windows using an executable-specific setting called "Compatibility Mode".[11]

An API differs from an application binary interface (ABI) in that an API is source code based while an ABI is binary based. For instance, POSIX provides APIs while the Linux Standard Base provides an ABI.[12][13]

Remote APIs

Remote APIs allow developers to manipulate remote resources through protocols, specific standards for communication that allow different technologies to work together, regardless of language or platform. For example, the Java Database Connectivity API allows developers to query many different types of databases with the same set of functions, while the Java remote method invocation API uses the Java Remote Method Protocol to allow invocation of functions that operate remotely, but appear local to the developer.[14][15]

Therefore, remote APIs are useful in maintaining the object abstraction in object-oriented programming; a method call, executed locally on a proxy object, invokes the corresponding method on the remote object, using the remoting protocol, and acquires the result to be used locally as return value.

A modification on the proxy object also will result in a corresponding modification on the remote object.[16]

Web APIs

Web APIs are the defined interfaces through which interactions happen between an enterprise and applications that use its assets, which also is a Service Level Agreement (SLA) to specify the functional provider and expose the service path or URL for its API users. An API approach is an architectural approach that revolves around providing a program interface to a set of services to different applications serving different types of consumers.[17]

When used in the context of web development, an API is typically defined as a set of specifications, such as Hypertext Transfer Protocol (HTTP) request messages, along with a definition of the structure of response messages, usually in an Extensible Markup Language (XML) or JavaScript Object Notation (JSON) format. An example might be a shipping company API that can be added to an eCommerce-focused website to facilitate ordering shipping services and automatically include current shipping rates, without the site developer having to enter the shipper's rate table into a web database. While "web API" historically virtually has been synonymous for web service, the recent trend (so-called Web 2.0) has been moving away from Simple Object Access Protocol (SOAP) based web services and service-oriented architecture (SOA) towards more direct representational state transfer (REST) style web resources and resource-oriented architecture (ROA).[18] Part of this trend is related to the Semantic Web movement toward Resource Description Framework (RDF), a concept to promote web-based ontology engineering technologies. Web APIs allow the combination of multiple APIs into new applications known as mashups.[19] In the social media space, web APIs have allowed web communities to facilitate sharing content and data between communities and applications. In this way, content that is created in one place dynamically can be posted and updated to multiple locations on the web.[20] For example, Twitter's REST API allows developers to access core Twitter data and the Search API provides methods for developers to interact with Twitter Search and trends data.


The design of an API has significant impact on its usage.[1] The principle of information hiding describes the role of programming interfaces as enabling modular programming by hiding the implementation details of the modules so that users of modules need not understand the complexities inside the modules.[21] Thus, the design of an API attempts to provide only the tools a user would expect.[1] The design of programming interfaces represents an important part of software architecture, the organization of a complex piece of software.[22]

Several authors have created recommendations for how to design APIs, such as Joshua Bloch,[23] Kin Lane,[24] and Michi Henning.[25]

Release policies

APIs are one of the more common ways technology companies integrate with each other. Those that provide and use APIs are considered as being members of a business ecosystem.[26]

The main policies for releasing an API are:[27]

  • Private: The API is for internal company use only.
  • Partner: Only specific business partners can use the API. For example, transportation network companies such as Uber and Lyft allow approved third-party developers to directly order rides from within their apps. This allows the companies to exercise quality control by curating which apps have access to the API, and provides them with an additional revenue stream.[28]
  • Public: The API is available for use by the public. For example, Microsoft makes the Microsoft Windows API public, and Apple releases its APIs Carbon and Cocoa, so that software can be written for their platforms.

Public API implications

An important factor when an API becomes public is its "interface stability". Changes by a developer to a part of it—for example adding new parameters to a function call—could break compatibility with clients that depend on that API.[29]

When parts of a publicly presented API are subject to change and thus not stable, such parts of a particular API should be documented explicitly as "unstable". For example, in the Google Guava library, the parts that are considered unstable, and that might change in the near future, are marked with the Java annotation @Beta.[30]

A public API can sometimes declare parts of itself as deprecated or rescinded. This usually means that part of the API should be considered a candidate for being removed, or modified in a backward incompatible way. Therefore, these changes allows developers to transition away from parts of the API that will be removed or not supported in the future.[31]

Client code may contain innovative or opportunistic usages that were not intended by the API designers. In other words, for a library with a significant user base, when an element becomes part of the public API, it may be used in diverse ways.[32]


API documentation describes what services an API offers and how to use those services, aiming to cover everything a client would need to know for practical purposes.

Documentation is crucial for the development and maintenance of applications using the API.[33] API documentation is traditionally found in documentation files but can also be found in social media such as blogs, forums, and Q&A websites.[34]

Traditional documentation files are often presented via a documentation system, such as Javadoc or Pydoc, that has a consistent appearance and structure. However, the types of content included in the documentation differs from API to API.[35]

In the interest of clarity, API documentation may include a description of classes and methods in the API as well as "typical usage scenarios, code snippets, design rationales, performance discussions, and contracts", but implementation details of the API services themselves are usually omitted.

Restrictions and limitations on how the API can be used are also covered by the documentation. For instance, documentation for an API function could note that its parameters cannot be null, that the function itself is not thread safe,[36] or that a decrement and cancel protocol averts self-trading. Because API documentation tends to be comprehensive, it is a challenge for writers to keep the documentation updated and for users to read it carefully, potentially yielding bugs.[29]

API documentation can be enriched with metadata information like Java annotations. This metadata can be used by the compiler, tools, and by the run-time environment to implement custom behaviors or custom handling.[37]

It is possible to generate API documentation in data-driven manner. By observing a large number of programs that use a given API, it is possible to infer the typical usages, as well the required contracts and directives.[38] Then, templates can be used to generate natural language from the mined data.

Copyright controversy

In 2010, Oracle Corporation sued Google for having distributed a new implementation of Java embedded in the Android operating system.[39] Google had not acquired any permission to reproduce the Java API, although permission had been given to the similar OpenJDK project. Judge William Alsup ruled in the Oracle v. Google case that APIs cannot be copyrighted in the U.S, and that a victory for Oracle would have widely expanded copyright protection and allowed the copyrighting of simple software commands:

To accept Oracle's claim would be to allow anyone to copyright one version of code to carry out a system of commands and thereby bar all others from writing its own different versions to carry out all or part of the same commands.[40][41]

In 2014, however, Alsup's ruling was overturned on appeal to the Court of Appeals for the Federal Circuit, though the question of whether such use of APIs constitutes fair use was left unresolved.[42]

In 2016, following a two-week trial, a jury determined that Google's reimplementation of the Java API constituted fair use, but Oracle vowed to appeal the decision.[43] Oracle won on its appeal, with the Court of Appeals for the Federal Circuit ruling that Google's use of the APIs did not qualify for fair use.[44] In 2019, Google appealed to the Supreme Court of the United States over both the copyrightability and fair use rulings. [45]


See also


  1. ^ a b c Clarke, Steven (2004). "Measuring API Usability". Dr. Dobb's. Retrieved 29 July 2016.
  2. ^ Odersky, Martin; Spoon, Lex; Venners, Bill (10 December 2008). "Combining Scala and Java". Retrieved 29 July 2016.
  3. ^ de Figueiredo, Luiz Henrique; Ierusalimschy, Roberto; Filho, Waldemar Celes. "The design and implementation of a language for extending applications". TeCGraf Grupo de Tecnologia Em Computacao Grafica. Retrieved 29 July 2016.
  4. ^ Sintes, Tony (2001-07-13). "Just what is the Java API anyway?". JavaWorld. Retrieved 29 July 2016.
  5. ^ Emery, David. "Standards, APIs, Interfaces and Bindings". Archived from the original on 2015-01-16. Retrieved 2016-08-08.
  6. ^ "". Retrieved 2011-12-18.
  7. ^ Fowler, Martin. "Inversion Of Control".
  8. ^ Fayad, Mohamed. "Object-Oriented Application Frameworks".
  9. ^ Lewine, Donald A. (1991). POSIX Programmer's Guide (PDF). O'Reilly & Associates, Inc. p. 1. Retrieved 2 August 2016.
  10. ^ West, Joel; Dedrick, Jason (2001). "Open source standardization: the rise of Linux in the network era" (PDF). Knowledge, Technology & Policy. 14 (2): 88–112. Retrieved 2 August 2016.
  11. ^ Microsogt (October 2001). "Support for Windows XP". Microsoft. p. 4. Archived from the original on 2009-09-26.
  12. ^ "LSB Introduction". Linux Foundation. 21 June 2012. Retrieved 2015-03-27.
  13. ^ Stoughton, Nick (April 2005). "Update on Standards" (PDF). USENIX. Retrieved 2009-06-04.
  14. ^ Bierhoff, Kevin (23 April 2009). "API Protocol Compliance in Object-Oriented Software" (PDF). CMU Institute for Software Research. Retrieved 29 July 2016.
  15. ^ Wilson, M. Jeff (2000-11-10). "Get smart with proxies and RMI". JavaWorld. Retrieved 29 July 2016.
  16. ^ Henning, Michi; Vinoski, Steve (1999). Advanced CORBA Programming with C++. Addison-Wesley. ISBN 978-0201379273. Retrieved 16 June 2015.
  17. ^ "API-fication" (PDF download). August 2014.
  18. ^ Benslimane, Djamal; Schahram Dustdar; Amit Sheth (2008). "Services Mashups: The New Generation of Web Applications". IEEE Internet Computing, vol. 12, no. 5. Institute of Electrical and Electronics Engineers. pp. 13–15.
  19. ^ Niccolai, James (2008-04-23), "So What Is an Enterprise Mashup, Anyway?", PC World
  20. ^ Parr, Ben. "The Evolution of the Social Media API". Mashable. Retrieved 26 July 2016.
  21. ^ Parnas, D.L. (1972). "On the Criteria To Be Used in Decomposing Systems into Modules" (PDF). Association for Computing Machinery. Retrieved 8 August 2016.
  22. ^ Garlan, David; Shaw, Mary (January 1994). "An Introduction to Software Architecture" (PDF). Advances in Software Engineering and Knowledge Engineering. 1. Retrieved 8 August 2016.
  23. ^ Bloch, Josh. "How to design a good API and why it matters" (PDF).
  24. ^ Lane, Kin (2016-03-14). "The Industry Guide to API Design" (PDF). Kin Lane via 3scale. Archived from the original (PDF) on 2016-03-15. Retrieved 2016-03-14.
  25. ^ Henning, Michi. "API: Design Matters".
  26. ^ de Ternay, Guerric (Oct 10, 2015). "Business Ecosystem: Creating an Economic Moat". BoostCompanies. Retrieved 2016-02-01.
  27. ^ Boyd, Mark (2014-02-21). "Private, Partner or Public: Which API Strategy Is Best for Business?". ProgrammableWeb. Retrieved 2 August 2016.
  28. ^ Weissbrot, Alison (7 July 2016). "Car Service APIs Are Everywhere, But What's In It For Partner Apps? | AdExchanger". ad exchanger. Retrieved 2 August 2016.
  29. ^ a b Shi, Lin; Zhong, Hao; Xie, Tao; Li, Mingshu (2011). An Empirical Study on Evolution of API Documentation. International Conference on Fundamental Approaches to Software Engineering. Lecture Notes in Computer Science. 6603. pp. 416–431. doi:10.1007/978-3-642-19811-3_29. ISBN 978-3-642-19810-6. Retrieved 22 July 2016.
  30. ^ "guava-libraries - Guava: Google Core Libraries for Java 1.6+ - Google Project Hosting". 2014-02-04. Retrieved 2014-02-11.
  31. ^ Oracle. "How and When to Deprecate APIs". Java SE Documentation. Retrieved 2 August 2016.
  32. ^ Mendez, Diego; Baudry, Benoit; Monperrus, Martin (2013). 2013 IEEE 13th International Working Conference on Source Code Analysis and Manipulation (SCAM). pp. 43–52. arXiv:1307.4062. doi:10.1109/SCAM.2013.6648183. ISBN 978-1-4673-5739-5.
  33. ^ Dekel, Uri; Herbsleb, James D. (May 2009). "Improving API Documentation Usability with Knowledge Pushing". Institute for Software Research, School of Computer Science. CiteSeerX
  34. ^ Parnin, Chris; Treude, Cristoph (May 2011). "Measuring API Documentation on the Web". Web2SE. Retrieved 22 July 2016.
  35. ^ Maalej, Waleed; Robillard, Martin P. (April 2012). "Patterns of Knowledge in API Reference Documentation" (PDF). IEEE Transactions on Software Engineering. Retrieved 22 July 2016.
  36. ^ Monperrus, Martin; Eichberg, Michael; Tekes, Elif; Mezini, Mira (3 December 2011). "What should developers be aware of? An empirical study on the directives of API documentation". Empirical Software Engineering. 17 (6): 703–737. arXiv:1205.6363. doi:10.1007/s10664-011-9186-4.
  37. ^ "Annotations". Sun Microsystems. Retrieved 2011-09-30..
  38. ^ Bruch, Marcel; Mezini, Mira; Monperrus, Martin (2010). Mining subclassing directives to improve framework reuse. 7th IEEE Working Conference on Mining Software Repositories (MSR 2010). pp. 141–150. CiteSeerX doi:10.1109/msr.2010.5463347. ISBN 978-1-4244-6802-7.
  39. ^ "Oracle and the End of Programming As We Know It". DrDobbs. 2012-05-01. Retrieved 2012-05-09.
  40. ^ "APIs Can't be Copyrighted Says Judge in Oracle Case". TGDaily. 2012-06-01. Retrieved 2012-12-06.
  41. ^ "Oracle America, Inc. vs. Google Inc" (PDF). Wired. 2012-05-31. Retrieved 2013-09-22.
  42. ^ Rosenblatt, Seth (May 9, 2014). "Court sides with Oracle over Android in Java patent appeal". CNET. Retrieved 2014-05-10.
  43. ^ "Google beats Oracle—Android makes "fair use" of Java APIs". Ars Technica. 2016-05-26. Retrieved 2016-07-28.
  44. ^ Decker, Susan (March 27, 2018). "Oracle Wins Revival of Billion-Dollar Case Against Google". Bloomberg Businessweek. Retrieved March 27, 2018.
  45. ^ Lee, Timothy (January 25, 2019). "Google asks Supreme Court to overrule disastrous ruling on API copyrights". Ars Technica. Retrieved February 8, 2019.

Further reading

Application Programming Interface for Windows

The Application Programming Interface for Windows (APIW) Standard is a specification of the Microsoft Windows 3.1 API drafted by Willows Software. It is the successor to previously proposed Public Windows Interface standard. It was created in an attempt to establish a vendor-neutral, platform-independent, open standard of the 16-bit Windows API not controlled by Microsoft.

Application programming interface key

An application programming interface key (API key) is a code passed in by computer programs calling an application programming interface (API) to identify the calling program, its developer, or its user to the Web site. API keys are used to track and control how the API is being used, for example to prevent malicious use or abuse of the API (as defined perhaps by terms of service).

Business Application Programming Interface

Business Application Programming Interface (BAPI) is used in mySAP to achieve business related functionalities. It is a remote-enabled function module which is provided by SAP.

Data Protection API

DPAPI (Data Protection Application Programming Interface) is a simple cryptographic application programming interface available as a built-in component in Windows 2000 and later versions of Microsoft Windows operating systems. In theory the Data Protection API can enable symmetric encryption of any kind of data; in practice, its primary use in the Windows operating system is to perform symmetric encryption of asymmetric private keys, using a user or system secret as a significant contribution of entropy.

For nearly all cryptosystems, one of the most difficult challenges is "key management" - in part, how to securely store the decryption key. If the key is stored in plain text, then any user that can access the key can access the encrypted data. If the key is to be encrypted, another key is needed, and so on. DPAPI allows developers to encrypt keys using a symmetric key derived from the user's logon secrets, or in the case of system encryption, using the system's domain authentication secrets.

The DPAPI keys used for encrypting the user's RSA keys are stored under %APPDATA%\Microsoft\Protect\{SID} directory, where {SID} is the Security Identifier of that user. The DPAPI key is stored in the same file as the master key that protects the users private keys. It usually is 64 bytes of random data.

In 2010 Elie Bursztein and Jean-Michel Picod presented an analysis of the protocol titled Reversing DPAPI and Stealing Windows Secrets Offline at Black Hat DC 2010. In addition to their briefing, Bursztein and Picod released DPAPIck which allows offline decryption of data encrypted with DPAPI. In 2012 Passcape Software published in their blog more detailed article on DPAPI internal logic and presented a tool for fully offline DPAPI decryption and analysis. Unlike previous one, the tool utilizes some old Windows bugs (for example, you can decrypt Windows 2000 DPAPI blobs without knowing the owner logon password) and is fully compatible with Windows 8 DPAPI data structure. In Windows 8 Microsoft changed the way the DPAPI logic works. Now multiple user keys can be used to derive an encryption key to decrypt the user masterkey which is used then to decode a single DPAPI blob.


In Unix-like operating systems, iconv (an abbreviation of internationalization conversion) is a command-line program and a standardized application programming interface (API) used to convert between different character encodings. "It can convert from any of these encodings to any other, through Unicode conversion."

Indexed Database API

The Indexed Database API (commonly referred to as IndexedDB) is a JavaScript application programming interface (API) provided by web browsers for managing a NoSQL database of JSON objects. It is a standard maintained by the World Wide Web Consortium (W3C).As an alternative to the Web storage standard, IndexedDB can provide more storage capacity. Web storage has fixed limits per website, but IndexedDB limits are "usually quite large, if they exist at all".Use cases for IndexedDB include caching web application data for offline availability. Some browser modules, such as devtools or extensions, may also use it for storage.

Internet Server Application Programming Interface

The Internet Server Application Programming Interface (ISAPI) is an N-tier API of Internet Information Services (IIS), Microsoft's collection of Windows-based web server services. The most prominent application of IIS and ISAPI is Microsoft's web server.

The ISAPI has also been implemented by Apache's mod_isapi module so that server-side web applications written for Microsoft's IIS can be used with Apache, and other third-party web servers like Zeus Web Server offer ISAPI interfaces.

Microsoft's web server application software is called Internet Information Services, which is made up of a number of "sub-applications" and is very configurable. ASP.NET is one such slice of IIS, allowing a programmer to write web applications in their choice of programming language (VB.NET, C#, F#) that's supported by the Microsoft .NET CLR. ISAPI is a much lower-level programming system, giving much better performance, at the expense of simplicity.


KulturNav is a Norwegian cloud-based software service, allowing users to create, manage and distribute name authorities and terminology, focusing on the needs of museums and other cultural heritage institutions. The software is developed by KulturIT ANS and the development project is funded by the Arts Council Norway.KulturNav is designed to enhance access to heritage information in archives, libraries and museums, working across institutions with common metadata. Thus many institutions can collaborate to build up a list of standard naming and terminology. The metadata is published as linked open data (LOD), which can be linked further against other LOD resources. The application programming interface (API) currently supports HTTP GET requests to read data. API calls are currently not authenticated or authorized. This means that the system returns only published content that is readable by any user. The system was developed within Play Framework together with Solr and jQuery.The company KulturIT, launched in 2013, is owned by five Norwegian and one Swedish museum. It is a non-profit organisation with all surplus going to development.The website was launched on 20 January 2015 and is currently being used by approximately 130 museums in Norway, Sweden and Åland. In March 2015 the Swedish national register of photography was in the process of being transferred to the KulturNav site. A register of Swedish architects is also available through Kulturnav.

List of Microsoft Windows application programming interfaces and frameworks

The following is a list of Microsoft APIs and frameworks.


Messaging Application Programming Interface (MAPI) is an API for Microsoft Windows which allows programs to become email-aware. While MAPI is designed to be independent of the protocol, it is usually used to communicate with Microsoft Exchange Server.

Microsoft CryptoAPI

The Microsoft windows platform specific Cryptographic Application Programming Interface (also known variously as CryptoAPI, Microsoft Cryptography API, MS-CAPI or simply CAPI) is an application programming interface included with Microsoft Windows operating systems that provides services to enable developers to secure Windows-based applications using cryptography. It is a set of dynamically linked libraries that provides an abstraction layer which isolates programmers from the code used to encrypt the data. The Crypto API was first introduced in Windows NT 4.0 and enhanced in subsequent versions.

CryptoAPI supports both public-key and symmetric key cryptography, though persistent symmetric keys are not supported. It includes functionality for encrypting and decrypting data and for authentication using digital certificates. It also includes a cryptographically secure pseudorandom number generator function CryptGenRandom.

CryptoAPI works with a number of CSPs (Cryptographic Service Providers) installed on the machine. CSPs are the modules that do the actual work of encoding and decoding data by performing the cryptographic functions. Vendors of HSMs may supply a CSP which works with their hardware.

Microsoft Speech API

The Speech Application Programming Interface or SAPI is an API developed by Microsoft to allow the use of speech recognition and speech synthesis within Windows applications. To date, a number of versions of the API have been released, which have shipped either as part of a Speech SDK or as part of the Windows OS itself. Applications that use SAPI include Microsoft Office, Microsoft Agent and Microsoft Speech Server.

In general, all versions of the API have been designed such that a software developer can write an application to perform speech recognition and synthesis by using a standard set of interfaces, accessible from a variety of programming languages. In addition, it is possible for a 3rd-party company to produce their own Speech Recognition and Text-To-Speech engines or adapt existing engines to work with SAPI. In principle, as long as these engines conform to the defined interfaces they can be used instead of the Microsoft-supplied engines.

In general, the Speech API is a freely redistributable component which can be shipped with any Windows application that wishes to use speech technology. Many versions (although not all) of the speech recognition and synthesis engines are also freely redistributable.

There have been two main 'families' of the Microsoft Speech API. SAPI versions 1 through 4 are all similar to each other, with extra features in each newer version. SAPI 5, however, was a completely new interface, released in 2000. Since then several sub-versions of this API have been released.


Netscape Plugin Application Programming Interface (NPAPI) is a deprecated (see below) application programming interface (API) that allows browser extensions to be developed. It was first developed for Netscape browsers, starting in 1995 with Netscape Navigator 2.0, but was subsequently adopted by other browsers. With the advent of HTML5 many software vendors have removed support for this API for security reasons.

In NPAPI architecture, a plugin declares content types (e.g. "audio/mp3") that it can handle. When the browser encounters a content type it cannot handle natively, it loads the appropriate plugin, sets aside space within the browser context for the plugin to render and then streams data to it. The plugin is responsible for rendering the data. The plugin runs in-place within the page, as opposed to older browsers that had to launch an external application to handle unknown content types.

NPAPI requires each plugin to implement and expose approximately 15 functions for initializing, creating, deleting and positioning plugin content. NPAPI also supports scripting, printing, full-screen plugins, windowless plugins and content streaming.

Netscape Server Application Programming Interface

The Netscape Server Application Programming Interface (NSAPI) is an application programming interface for extending server software, typically web server software.

Remote Application Platform

Remote Application Platform (RAP, formerly Rich Ajax Platform) Project is an open-source software project under the Eclipse Technology Project which aims to enable software developers to build Ajax-enabled rich Internet applications by using the Eclipse development model, plugins and a Java-only application programming interface (API). It can be considered a counterpart for web development to the Rich Client Platform (RCP). The API is very similar to RCP so developers who know RCP can reuse extant knowledge. RAP encourages sharing source code between RCP and RAP applications to reduce the development effort for business applications that need both desktop-based and web-based front ends.

Server Application Programming Interface

In computing, Server Application Programming Interface (SAPI) is the direct module interface to web servers such as the Apache HTTP Server, Microsoft IIS, and Oracle iPlanet Web Server. Microsoft uses the term Internet Server Application Programming Interface (ISAPI), and the defunct Netscape web server used the term Netscape Server Application Programming Interface (NSAPI) for the same purpose. In other words, SAPI is an application programming interface (API) provided by the web server to help other developers in extending the web server capabilities.

As an example, PHP has a direct module interface called SAPI for different web servers; in the case of PHP 5 and Apache 2.0 on Windows, it is provided in the form of a DLL file called php5apache2.dll, which is a module that, among other functions, provides an interface between PHP and the web server, implemented in a form that the server understands. This form is what is known as a SAPI.

Different kinds of SAPIs exist for various web-server extensions. For example, in addition to those listed above, other SAPIs for the PHP language include the Common Gateway Interface (CGI) and command-line interface (CLI).

Telephony Application Programming Interface

The Telephony Application Programming Interface (TAPI) is a Microsoft Windows API, which provides computer telephony integration and enables PCs running Microsoft Windows to use telephone services. Different versions of TAPI are available on different versions of Windows. TAPI allows applications to control telephony functions between a computer and telephone network for data, fax, and voice calls. It includes basic functions, such as dialing, answering, and hanging up a call. It also supports supplementary functions, such as hold, transfer, conference, and call park found in PBX, ISDN, and other telephone systems.

TAPI is used primarily to control either modems or, more recently, to control business telephone system (PBX) handsets. When controlling a PBX handset, the driver is provided by the manufacturer of the telephone system. Some manufacturers provide drivers that allow the control of multiple handsets. This is traditionally called "third-party control". Other manufacturers provide drivers that allow the control of a single handset. This is called "first-party control". Third-party drivers are designed to allow applications to see and/or control multiple extensions at the same time. Some telephone systems only permit one third-party connection at a time. First-party drivers are designed to allow applications to monitor and/or control one extension at a time. Telephone systems naturally permit many of these connections simultaneously. Modem connections are by nature first-party.

TAPI can also be used to control voice-enabled telephony devices, including voice modems and dedicated hardware such as Dialogic cards.


WebUSB is a proposed JavaScript application programming interface (API) standard for securely providing access to USB devices from web pages.It was published by the Web Platform Incubator Community Group. As of September 2018, it was still in Editor's draft status, and the only web browser to support it was Google Chrome.WebUSB was enabled by default in Chrome 61 on September 5 2017, after which privacy and security concerns were raised.


A Web API is an application programming interface for either a web server or a web browser. It is a web development concept, usually limited to a web application's client-side (including any web frameworks being used), and thus usually does not include web server or browser implementation details such as SAPIs or APIs unless publicly accessible by a remote web application.

Process management
Memory management and
resource protection
Storage access and
file systems
Miscellaneous concepts

This page is based on a Wikipedia article written by authors (here).
Text is available under the CC BY-SA 3.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.