An HTML documentation generator for Coq source files
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coq2html: an HTML documentation generator for Coq


coq2html is an HTML documentation generator for Coq source files. It is an alternative to the standard coqdoc documentation generator distributed along with Coq. The major feature of coq2html is its ability to fold proof scripts: in the generated HTML, proof scripts are initially hidden, but can be revealed one by one by clicking on the "Proof" keyword. Here is an example of folding in action.

Compatibility: to produce cross-references, coq2html reads .glob files produced by Coq. The format of those files is undocumented and changes silently between major releases of Coq. The current version of coq2html is believed to be compatible with Coq 8.8, 8.7, and 8.6.

History: coq2html was developed and originally distributed as part of the CompCert project when it became clear that the coqdoc of the time was not able to format the CompCert Coq sources the desired way. This is the first release of coq2html as a stand-alone tool, independent from CompCert.


          coq2html [options] file.glob ... file.v ...

Summary of options:

Option Summary
-base COQDIR Set the name space for the modules being processed
-coqlib URL Set base URL for Coq standard library
-d DIR Output files to directory DIR (default: current directory)
-external URL COQDIR Set base URL for linking references whose names start with COQDIR
-no-css Do not add coq2html.css to the output directory
-redirect Generate redirection files
-short-names Use short, unqualified module names in the output

HTML generation

coq2html takes one or several Coq source files with extension .v, pretty-prints their contents, and saves the generated HTML text to files with extension .html.

By default all files are generated in the current working directory. The -d DIR option makes coq2html generate files in the given directory instead. The directory DIR must exist before coq2html is started.

In addition to HTML files, coq2html also produces two auxiliary files in the output directory given by -d or by default in the current directory:

  • coq2html.css: the style sheet for the generated HTML files;
  • coq2html.js: auxiliary JavaScript code that implements proof folding.

The -no-css option suppresses the generation of the coq2html.css file. Users of this option are expected to provide their own style sheet. It must be named coq2html.css and it must reside in the directory where coq2html generates its files.

For a source file F.v in the current directory and if no -base option is given, the generated HTML file is named F.html. If the source file is in a subdirectory, or if the -base option is given, a Coq-style fully-qualified name is used as the name of the generated HTML file, as shown below:

-base option Source file name Generated HTML file name
none F.v F.html
none D/E/F.v D.E.F.html
-base A.B.C F.v A.B.C.F.html
-base A.B.C D/E/F.v A.B.C.D.E.F.html

As strange as it looks, this file naming convention is compatible with that of coqdoc and ensures that file names are globally unique across multiple Coq libraries and packages.

The fully-qualified name is also used to produce the title of the generated HTML page. In the last example above, the fully-qualified name is A.B.C.D.E.F and the title of the page will be Module A.B.C.D.E.F. If the -short-names option is given, the unqualified, local name is used instead, giving Module F as title.

Earlier versions of coq2html used short names F.html instead of fully-qualified names to name the generated HTML files. For backward compatibility, the -redirect option can be given. It causes an additional F.html file to be generated, containing a HTTP redirection to the file A.B.C.D.E.F.html. The -redirect option is silently ignored if no -base option is given.


coq2html can generate cross-references as hyperlinks from uses to definitions of Coq names, provided the appropriate .glob files are given on the command-line.

A cross-reference file F.glob is generated by the Coq compiler coqc when it processes the F.v source file. (Unless the -no-glob option is passed to coqc; don't do that.) When giving F.v as argument to coq2html, also give F.glob as argument, so that coq2html can use those cross-references to produce hyperlinks.

Important: if the source files are compiled within a Coq namespace, you must give a -base option to coq2html indicating this namespace. For example, if you compile with

        coqc -R A.B.C .

meaning that the current directory means namespace A.B.C, then you must invoke coq2html with

        coq2html -base A.B.C

By default, cross-references are generated if the referenced definition is

  • in one of the .glob files given to coq2html on the command line, or
  • in the Coq standard library.

For this reason, to get better cross-referencing, you should either do a single run of coq2html with all the .v and .glob files of your Coq development, or give all the .glob files of your library to every run of coq2html on every .v file.

The cross-references to the Coq standard library use the online version of this library at, which corresponds to the latest release of Coq. If you wish to reference a specific version of the standard library, use the -coqlib option, e.g.

        coq2html -coqlib ...

for the 8.5pl3 version of the standard library.

Using the -external option, you can add cross-references to other external libraries whose coqdoc or coq2html-generated documentation is accessible online. For example,

        coq2html -external mathcomp ...

should produce cross-references to the mathcomp library modules. (Warning: untested feature.)

Markup language for documentation comments

Documentation comments start with (** (two stars followed by a space) or (**r (two stars, the "r" character, one space).

     (** This is a documentation comment. *)
     (**r This is a right-aligned documentation comment. *)
     (* This is a regular comment. *)

Regular, non-documentation comments are removed from the HTML output, except within proof scripts, where they are kept as is.

Documentation comments of the (** kind are formatted as described next, then inserted as a paragraph in the HTML output. Right-aligned documentation comments of the (**r kind are formatted likewise, but do not start a paragraph. Instead, they hang to the right of the Coq code on the same line. Example:

     (** This is the type of lists. *)

     Inductive list (A: Type) : Type :=
     | nil                         (**r the empty list *)
     | cons (hd: A) (tl: list A).  (**r the  nonempty list [hd::tl] *)

Inline Coq text

Within a documentation comment, text within square brackets [...] is taken to be Coq text and is formatted in monospace font. You can write [x + S y] and will get x + S y. Square brackets nest properly, hence [[x;y]] gives [x;y].

Inline HTML

Within a documentation comment, text between hash signs #...# is treated as pure HTML and copied verbatim to the output, without escaping of HTML special characters. Hence, #...# escapes are the only way to insert HTML tags. Example:

    (** 32-bit integers are less than #2<sup>32</sup># *)

Verbatim text

Verbatim text starts with << on a line by itself and ends with >> on a line by itself. The lines between those two markers are copied to the output, in typewriter font, respecting newlines. Example:

(** This is normal documentation text.
        This is verbatim text.
        Second line of verbatim text.
    This is normal text again. *)

Warning: << and >> must be at the beginning of a line, without any space before.


Section titles are denoted by one to four * characters at the beginning of a documentation comment:

    (** * Section title *)
    (** ** Subsection *)
    (** *** Sub-sub section *)
    (** **** Sub-sub-sub section *)

The section title extends until the end of the documentation comment.

Lists of items

Lists start with a dash - at the beginning of the line. Subsequent lines starting with a dash are items in the list. A blank line terminates the list. Example:

(** A list is either:
-     [nil], denoting the empty list;
-     [cons h t], also written [h :: t], denoting the nonempty list
      with head [h] and tail [t].

  If we remove the [nil] case and declare a [CoInductive], we get infinite 
  streams instead of lists. *)

Nested lists are built using two, three or four dashes instead of one:

- Outer list, item #1
-- Inner list, item #1
-- Inner list, item #2
- Outer list, item #2

Special handling of proof scripts

Proof scripts are Coq text (outside comments) that

  • starts with Proof or Next Obligation at the beginning of a line;
  • ends with Qed. or Defined. or Save. or Admitted. or Abort. at the end of a line.

A proof script can start and end on the same line, e.g. Proof. auto. Qed.

Proof scripts are formatted in a smaller font and folded by default, leaving only the starting line (Proof, etc) visible. Clicking on this first line displays the whole proof script.

The syntax of proof scripts is strict. In particular, after stating a Theorem or Lemma, it does not work to omit the Proof keyword and start the script immediately, nor to abort it immediately with Admitted. or Abort.. Likewise, the dot . must follow Qed, Defined, etc, without spaces. For example, the following proof scripts won't be properly formatted:

Lemma x:...
auto. Qed.                      (* No "Proof." to mark the beginning of the script. *)

Lemma x:...
Admitted.                       (* No "Proof." to mark the beginning of the script. *)

Lemma x:...
Proof. auto. Defined .          (* Whitespace between "Defined" and "." *)

Lemma x:...  Proof. Admitted.   (* "Proof" must start a new line. *)