Serialization library and protocol for machine interaction with the Coq proof assistant

$ opam install coq-serapi
$ sertop --help

SerAPI is a library for machine-to-machine interaction with the Coq proof assistant,
with particular emphasis on applications in IDEs, code analysis tools, and machine learning.
SerAPI provides automatic serialization of Coq's internal
OCaml datatypes from/to JSON or
S-expressions (sexps).

SerAPI is a proof-of-concept and should be considered
alpha-quality. However, it is fully functional and supports, among
other things, asynchronous proof checking, full-document parsing, and
serialization of Coq's core datatypes. SerAPI can also be run as
thread, providing a self-contained Coq system inside the
browser. Typical load times in Google Chrome are less than a second.

The main design philosophy of SerAPI is to make clients' lives easy,
by providing a convenient, robust interface that hides most
of the scary details involved in interacting with Coq.

Feedback from Coq users and developers is very welcome and intrinsic
to the project. We are open to implementing new features and exploring
new use cases.

Documentation and Help:

API WARNING: The protocol is experimental and may change often.

Quick Overview and Install:

SerAPI can be installed as the OPAM package coq-serapi.
See build instructions for manual installation. The experimental
in-browser version is also online.

SerAPI provides an interactive "Read-Print-Eval-Loop" sertop, a
batch-oriented compiler sercomp, and a batch-oriented tokenizer sertok.
See the manual pages and --help pages of each command for more details.

To get familiar with SerAPI we recommend launching the sertop REPL,
as it provides a reasonably human-friendly experience:

$ rlwrap sertop --printer=human

You can then input commands. Ctrl-C will interrupt a busy Coq
process in the same way it interrupts coqtop.

The program sercomp provides a command-line interface to some
key functionality of SerAPI and can be used for batch processing
of Coq documents, e.g., to serialize Coq source files from/to lists of
S-expressions of Coq vernacular sentences. See sercomp --help for some
usage examples and an overview of the main options. The program sertok
provides similar functionality at the level of Coq source file tokens.

Protocol Commands:

Interaction with sertop is done using commands, which can be optionally tagged in the form of (tag cmd); otherwise, an automatic tag will be assigned.
For every command, SerAPI will always reply with (Answer tag Ack) to indicate that the command was successfully parsed and delivered to Coq, or with a SexpError if parsing failed.

There are three categories of commands:

  • Document manipulation: Add, Cancel, Exec, ...: these commands instruct Coq to perform some action on the current document.
    Every command will produce zero or more different tagged answers, and a final answer (Answer tag Completed), indicating that there won't be more output.

    SerAPI document commands are an evolution of the OCaml STM API, here and here you can find a few informal notes on how it works. We are working on a more detailed specification, for now you can get some more details in the issue tracker.

  • Queries: (Query ((opt value) ...) kind):

    Queries stream Coq objects of type kind. This can range from options, goals and hypotheses, tactics, etc.
    The first argument is a list of options: preds is a list of conjunctive filters, limit specifies how many values the query may return.
    pp controls the output format: PpSer for full serialization, or PpStr for "pretty printing". For instance:

    (tag (Query ((preds (Prefix "Debug")) (limit 10) (pp PpSexp)) Option))

    will stream all Coq options that start with "Debug", limiting to the first 10 and printing the full internal Coq datatype:

    (CoqOption (Default Goal Selector)
       ((opt_sync true) (opt_depr false) (opt_name "default goal selector")
       (opt_value (StringValue 1))))

    Options can be omitted, as in: (tag (Query ((limit 10)) Option)), and
    currently supported queries can be seen here

  • Printing: (Print opts obj): The Print command provides access to the Coq pretty printers.
    Its intended use is for printing (maybe IDE manipulated) objects returned by Query.


SerAPI 0.11.x is based on Coq 8.11. These days, most work related to
SerAPI is directly happening over Coq's upstream
itself. The main objective is to improve the proof-document model; building
a rich query language will be next.

Clients and Users:

SerAPI has been used in a few contexts already, we provide a few
pointers here, feel free to add your own!

  • jsCoq allows you to run Coq in
    your browser. jsCoq is the predecessor of SerAPI and will shortly be
    fully based on it.

  • mCoq is a tool for mutation analysis
    of Coq projects, based on serializing and deserializing Coq code via SerAPI.
    See the accompanying paper
    for more details and an evaluation of the tool on several large projects.

  • elcoq, an emacs technology
    demo based on SerAPI by Clément Pit-Claudel. elcoq is not fully
    functional but illustrates some noteworthy features of SerAPI.

  • PeaCoq, a Coq IDE for the
    browser, has an experimental branch that uses SerAPI.

  • GrammaTech's Software Evolution Library (SEL)
    provides tools for programmatically modifying and evaluating software. SEL operates
    over multiple software representations including source code in
    several languages and compiled machine code. Its Coq module uses
    SerAPI to serialize Coq source code into ASTs, which are parsed into
    Common Lisp objects for further manipulation. GrammaTech uses this
    library to synthesize modifications to software so that it satisfies
    an objective function, e.g., a suite of unit tests.
    SerAPI support was added to SEL by Rebecca Swords.

  • CoqGym is a Coq-based learning environment for theorem proving.
    It uses SerAPI to interact with Coq and perform feature-extraction. Its author notes:

    See also the paper describing CoqGym.

  • Proverbot9001 is a proof search system based on machine
    learning techniques, and uses SerAPI to interface with Coq.
    See also the paper describing the system.

  • SerAPI is being used to improve the Coq regression proof
    selection tool iCoq,
    see the paper.

  • SerAPI is being used in additional software testing and machine learning projects; we will
    update this list as papers get out of embargo.

Quick Demo (not always up to date):

$ rlwrap sertop --printer=human
(Add () "Lemma addn0 n : n + 0 = n. Proof. now induction n. Qed.")
  > (Answer 0 Ack)
  > (Answer 0 (Added 2 ((fname "") (line_nb 1) (bol_pos 0) (line_nb_last 1) (bol_pos_last 0) (bp 0) (ep 26))
  >            NewTip))
  > ...
  > (Answer 0 (Added 5 ... NewTip))
  > (Answer 0 Completed)

(Exec 5)
  > (Answer 1 Ack)
  > (Feedback ((id 5) (route 0) (contents (ProcessingIn master))))
  > ...
  > (Feedback ((id 5) (route 0) (contents Processed)))
  > (Answer 1 Completed)

(Query ((sid 3)) Goals)
  > (Answer 2 Ack)
  > (Answer 2
  >  (ObjList ((CoqGoal ((fg_goals (((name 5) (ty (App (Ind ...))))
                         (bg_goals ()) (shelved_goals ()) (given_up_goals ()))))))
  > (Answer 2 Completed)

(Query ((sid 3) (pp ((pp_format PpStr)))) Goals)
  > (Answer 3 Ack)
  > (Answer 3 (ObjList ((CoqString
  >   "\
  >    \n  n : nat\
  >    \n============================\
  >    \nn + 0 = n"))))
  > (Answer 3 Completed)

(Query ((sid 4)) Ast)
  > (Answer 4 Ack)
  > (Answer 4 (ObjList ((CoqAst ((((fname "") (line_nb 1) (bol_pos 0) (line_nb_last 1)
  >                                (bol_pos_last 0) (bp 34) (ep 50)))
  > ...
  >            ((Tacexp
  >              (TacAtom
  >                (TacInductionDestruct true false
  > ...
  > (Answer 4 Completed)

(pp_ex (Print ((sid 4) (pp ((pp_format PpStr)))) (CoqConstr (App (Rel 0) ((Rel 0))))))
  > (Answer pp_ex Ack)
  > (Answer pp_ex(ObjList((CoqString"(_UNBOUND_REL_0 _UNBOUND_REL_0)"))))

(Query () (Vernac "Print nat. "))
  > (Answer 6 Ack)
  > (Feedback ((id 5) (route 0) (contents
  >    (Message Notice ()
  >    ((Pp_box (Pp_hovbox 0) ...)
  > (Answer 6 (ObjList ()))
  > (Answer 6 Completed)

(Query () (Definition nat))
  > (Answer 7 Ack)
  > (Answer 7 (ObjList ((CoqMInd (Mutind ....)))))
  > (Answer 7 Completed)

Technical Report:

There is a brief technical report
describing the motivation, design, and implementation of SerAPI. If you are using
SerAPI in a project, please cite the technical report in any related publications:

  title = {{SerAPI: Machine-Friendly, Data-Centric Serialization for Coq}},
  author = {Gallego Arias, Emilio Jes{\'u}s},
  url = {},
  institution = {MINES ParisTech},
  year = {2016},
  month = Oct,

Developer Information

Technical Details

SerAPI has four main components:

  • serapi, an extended version of the current IDE protocol;

  • serlib, a library providing automatic de/serialization of most Coq data structures using ppx_conv_sexp. This should be eventually incorporated into Coq itself. Support for ppx_deriving_yojson is work in progress;

  • sertop, sertop_js, toplevels offering implementations of the protocol;

  • sercomp, sertok, command-line tools providing access to key features of serlib.

Building your own toplevels using serlib and serapi is encouraged.

Advanced Use Cases

With a bit more development effort, you can also:

  • Use SerAPI as an OCaml library. The low-level serialization library
    serlib/ and the higher-level SerAPI protocol in
    serapi/serapi_protocol.mli can be
    linked standalone.

  • Use SerAPI's web worker JavaScript Worker
    from your web/node application. In this model, you communicate with SerAPI using
    the typical onmessage/postMessage worker API. Ready-to-use builds
    may be found at
    here, we
    provide an example REPL at:

We would also like to provide a Jupyter/IPython kernel.

Developer/Users Mailing List

SerAPI development is mainly discussed on GitHub
and in the Gitter channel.
You can also use the jsCoq mailing list by subscribing at:

The mailing list archives should also be available at the Gmane group: You can post to the list
using nntp.


SerAPI has been developed at the
Centre de Recherche en Informatique of
MINES ParisTech (former École de
Mines de Paris) and was partially supported by the
FEEVER project.

18 Feb 2020
>= "1.7.0"
>= "v0.11.0" & < "v0.15"
>= "4.2.1"
build & >= "1.5-3" & < "2.0"
>= "1.2.0"
>= "v0.11.0"
>= "1.8.0"
>= "1.0.0"
>= "8.11.0" & < "8.12"
>= "4.07.0"
Reverse Dependencies