Gemini (protocol)

From Wikipedia, the free encyclopedia
Developed bySolderpunk et al.
IntroducedJune 2019 (2019-06)
Filename extension
.gmi, .gmni, .gemini
Internet media typetext/gemini (unofficial)
Type codeTEXT
Developed bySolderpunk et al.
Latest release
30 January 2022; 19 months ago (2022-01-30)
Type of formatMarkup language
Open format?Yes

Gemini is an application-layer internet communication protocol for accessing remote documents, similar to the Hypertext Transfer Protocol (HTTP) and Gopher. It comes with a special document format, commonly referred to as "gemtext", which allows linking to other documents. Started by a pseudonymous person known as Solderpunk, the protocol is being finalized collaboratively and as of October 2022, has not been submitted to the IETF organization for standardization.


The Gemini project was started in June 2019 by Solderpunk. Additional work has been done by an informal community of users. According to Solderpunk's FAQ, Gemini is not intended to replace Gopher or HTTP, but to co-exist with them.[1] Much of the development happened on the Gemini mailing list until the list disappeared at the end of 2021 due to a hardware issue.[2] The creation of the Usenet newsgroup comp.infosystems.gemini in October 2021 was the first new newsgroup in the Big Eight hierarchy in eight years.[3]


The Gemini specification defines both the Gemini protocol and a native file format for that protocol, analogous to HTML for HTTP, known as "gemtext". The design is inspired by Gopher, but with modernisation such as mandatory use of Transport Layer Security (TLS) for connections and a hypertext format as native content type.[4]

The design is deliberately not easily extensible, in order to meet a project goal of simplicity.[5]


Gemini is designed within the framework of the Internet protocol suite and like HTTP/S, Gemini functions as a request–response protocol in the client–server computing model. A Gemini server should listen on TCP port 1965. A Gemini browser, for example, may be the client and an application running on a computer hosting a Gemini site may be the server. The client sends a Gemini request message to the server, and the server sends back a response message. Gemini uses a separate connection to the same server for every resource request.[6]

Gemini mandates the use of TLS with privacy-related features and trust on first use (TOFU) verification being strongly suggested.[7]

Gemini resources are identified and located on the network by Uniform Resource Locators (URLs), using the URI scheme gemini://. A Gemini request consists only of such a URL, terminated by CRLF; the header of a Gemini response consists of a two-digit status code, a space, and a "meta" field, also terminated by CRLF. If the server is successful in finding the requested file, the "meta" field is the MIME type of the returned file and after the header follows the file data.

Example session
20 text/gemini
# Example Title
Welcome to my Gemini capsule.
* Example list item
=> gemini:// Link text

Gemtext format[edit]

Gemtext format is line-oriented and the first three characters of a line determine its type. The syntax includes markup for headlines, flat list items, pre-formatted text, quotes and link lines. As with HTTP hypertext, URIs are encoded as hyperlinks to form interlinked hypertext documents in the Gemini "web", which users refer to as Geminispace.[1]


"Geminispace" denotes the whole of the public resources that are published on the Internet by the Gemini community via the Gemini protocol. Thus, Gemini spans an alternative communication web, with hypertext documents, including hyperlinks to other resources easily accessible to the user.[1]

As of February 2023, Geminispace consists of around 2300 online known Gemini appearances ("capsules") identified by crawling over 490,000 URIs.[8]


Amfora - Gemini client
AmiGemini - Gemini client
Gemini clients include:
Name Platform License Written in
Amfora Terminal (TUI) GPL 3.0 Go
AmiGemini GUI (Intuition) MIT C, Intuition
asuka Terminal (TUI) MIT Rust, ncurses
AV-98 Terminal (CLI) 2 Clause BSD Python
Bollux Terminal MIT Bash
Bombadillo Terminal GPL 3.0 Go
Buran App (Android) GPL 3.0 Kotlin
Castor GUI (GTK) MIT Rust, GTK
Castor9 GUI (Plan 9) C
Deedum App (Android and iOS) GPL 3.0 Flutter, Dart
Diohsc Terminal (CLI) GPL 3.0 Haskell
dillo-gemini Plugin (Dillo) FSFAP Shell
Elaho (gemini-ios) App (iOS) MPL 2.0 Swift
Elpher GUI (Emacs) GPL 3.0 Emacs Lisp
Fafi GUI MIT Racket
GemiNaut GUI (Windows) GPL 3.0 C# for Microsoft Windows
gemini.filter.dpi Plugin (Dillo) MIT Go
Geopard GUI (GTK) GPL 3.0 Rust, GTK
gmni Terminal (CLI) GPL 3.0 C
gplaces Terminal (CLI) GPL 3.0 or later C
Jimmy App (macOS) MIT Swift
Kristall GUI (Qt) GPL 2.0 C++, Qt
Lagrange GUI (Windows, macOS, Linux) 2 Clause BSD C, SDL
Moonlander GUI (GTK) MIT Rust, GTK
Offpunk Terminal (CLI) 2 Clause BSD Python
Rocketeer App (iOS, macOS) Swift
Seren App (Android) Kotlin
Starfish GUI (elementary OS/Linux) GPL 3.0 Vala, GTK
Telescope Terminal (TUI) ISC C
Twin Peaks GUI (Windows) GPL 3.0 C#
VIRGIL99 Terminal (TI-99) Assembly language

The Gemini software list covers client, server, libraries, and tools.[9]
Gemini-to-HTTP proxy server gateways such as can be used by web browsers lacking Gemini support.[10]


Gemini is praised for its simplicity but criticized for "excluding people who use ordinary web browsers".[11] Gemini's usefulness has been said to be "dependent on the kinds of content available on Gemini and whether it appeals or not".[5] Stéphane Bortzmeyer has said Gemini is retro but with modern features.[12] In a blog post covering the technical aspects of the protocol, Daniel Stenberg believed it can work and serve its community, but included criticisms on a number of design decisions, such as its reliance on a trust-on-first-use model and ambiguity in the URL specification.[13] He suggests splitting the specification into three separate parts (protocol, URL syntax, media type) and expanding each with more exact syntax descriptions and examples. Ambiguity in the spec is a barrier to cURL support for Gemini.

See also[edit]


  1. ^ a b c "Project Gemini FAQ". Archived from the original on 22 June 2020. Retrieved 26 June 2020.
  2. ^ "Gemini Info Page". Archived from the original on 2021-10-20. Retrieved 2021-10-20.
  3. ^ "Gemini Usenet Newsgroup". Archived from the original on 2021-10-26. Retrieved 2021-10-26.
  4. ^ "Project Gemini Speculative Specification v0.16.1". 2023-03-23. 5 The text/gemini media type. Response bodies of type "text/gemini" are a kind of lightweight hypertext format, which takes inspiration from gophermaps and from Markdown.{{cite web}}: CS1 maint: url-status (link)
  5. ^ a b Edge, Jake (2021-02-10). "Visiting another world". Retrieved 2021-02-19.
  6. ^ "Project Gemini Speculative Specification v0.16.1". 2023-03-23. 1 Overview. Connections are closed at the end of a single transaction and cannot be reused.{{cite web}}: CS1 maint: url-status (link)
  7. ^ "Project Gemini Speculative Specification". 2020-11-29. Archived from the original on 2021-05-12. Retrieved 2021-06-25. 4.2 Server certificate validation. Clients can validate TLS connections however they like (including not at all) but the strongly recommended approach is to implement a lightweight "TOFU" certificate-pinning system which treats self-signed certificates as first-class citizens.
  8. ^ "Statistics on the Gemini space". Proxied gemini://
  9. ^ "Gemini software".
  10. ^ "About".
  11. ^ Proven, Liam (27 Jan 2022). "Toaster-friendly alternative web protocol Gemini attracts criticism for becoming exclusive clique". The Register.
  12. ^ "Gemini, a modern protocol that looks retro". Retrieved 2022-10-30.
  13. ^ Stenberg, Daniel (28 May 2023). "The Gemini protocol seen by this HTTP client person".

External links[edit]