Specifying Options

Stainless’s command line options have the form --option or --option=value. To enable a flag option, use --option=true or on or yes, or just --option. To disable a flag option, use --option=false.

Additionally, if you need to pass options to the scalac frontend of Stainless, you can do it by using a single dash -. For example, try -Ybrowse:typer.

The rest of this section presents some of the command-line options that Stainless recognizes. For a short (but always up-to-date) summary, you can also invoke stainless --help.

Choosing which Stainless feature to use

The first group of options determines which feature of Stainless will be used. By default, --verification is chosen.

  • --verification

    Proves or disproves function contracts, as explained in the Verification conditions section.

  • --eval

    Evaluate parameterless functions and report their body’s value and whether or not their postcondition holds.

  • --genc

    Convert stainless code to C (implies –batched, default: false). See documentation section for generating C code.

  • --coq

    Transform the program into a Coq program, and let Coq generate subgoals automatically

  • --type-checker

    Use type checker inspired by System FR to generate verification conditions. Default is true and is strongly recommended; using false reverts to an old verification-condition generator.

  • --infer-measures=[yes|no|only] (default: yes)

    Infers measures for recursive functions which do not already have one.

  • --check-measures=[true|false] (default: true)

    Check termination of functions with measures, ie. whether measures decrease between recursive calls.

  • --testgen

    Proves or disproves function contracts (like --verification) and attempts to create Scala test cases from reported counter-examples.

  • --genc-testgen

    Like --testgen, but generates C test cases using GenC.

  • --help

    Prints a helpful message, then exits.

Additional top-level options

These options are available to all Stainless components:

  • --watch

    Re-run the selected analysis components upon file changes, making the program analysis interactive and significantly more efficient than restarting stainless manually.

  • --no-colors

    Disable colored output and non-ascii characters (consider this option for better support in IDEs)

  • --compact

    Reduces the components’ summaries to only the invalid elements (e.g. invalid VC).

  • --debug=d1,d2,...

    Enables printing detailed messages for the components d1,d2,… . Available components include:

    • solver (SMT solvers and their wrappers)

    • termination (Termination analysis)

    • timers (Timers, timer pools)

    • trees (Manipulation of trees)

    • verification (Verification)

    • full-vc (Display VCs before and after simplification)

    • type-checker (Type checking of the final program for VC generation)

    • type-checker-vcs (Generation of VCs by the type-checker)

    • derivation (Dump typing derivations)

  • --functions=f1,f2,...

    Only consider functions f1, f2, … . This applies to all functionalities where Stainless manipulates the input in a per-function basis.

    Stainless will match against suffixes of qualified names. For instance: --functions=List.size will match the method stainless.collection.List.size, while --functions=size will match all methods and functions named size. This option supports _ as wildcard: --functions=List._ will match all List methods.

  • --solvers=s1,s2,...

    Use solvers s1, s2,… . If more than one solver is chosen, all chosen solvers will be used in parallel, and the best result will be presented. By default, the nativez3 solver is picked.

    Some solvers are specialized in proving verification conditions and will have a hard time finding a counterexample in the case of an invalid verification condition, whereas some are specialized in finding counterexamples, and some provide a compromise between the two. Also, some solvers do not as of now support higher-order functions.

    Available solvers include:

    • nativez3

      Native Z3 with z3-templates for unfolding recursive functions (default).

    • smt-cvc4

      CVC4 through SMT-LIB. An algorithm within Stainless takes up the unfolding of recursive functions, handling of lambdas etc. To use this or any of the following CVC4-based solvers, you need to have the cvc4 executable in your system path (the latest unstable version is recommended).

    • smt-z3

      Z3 through SMT-LIB. To use this or the next solver, you need to have the z3 executable in your program path (the latest stable version is recommended). Inductive reasoning happens on the Stainless side (similarly to smt-cvc4).

    • unrollz3

      Native Z3, but inductive reasoning happens within Stainless (similarly to smt-z3).

    • princess

      Princess solver through its native interface (uses princess-templates) during unfolding. This is a full-stack JVM solver and enables Stainless to run without external solver dependencies.

  • --timeout=t

    Set a timeout for each attempt to prove one verification condition/ repair one function (in sec.) When using the --eval component, one should use --max-calls instead.

  • --cache

    Use persistent cache on disk to save the state of the verification and/or termination analyses.

  • --cache-dir=<directory>

    Specify in which directory the cache files generated by --cache and other options should be stored. Defaults to .stainless-cache/.

  • --json=<file>

    Export the verification and/or termination analyses to the given file.

  • --extra-deps=org:name_scalaVersion:version,...

    Fetch the specified dependencies, and add their sources to the set of files processed by Stainless. Each dependency must be available as a source JAR from MavenCentral, the EPFL-LARA bintray organization, your local Ivy database, or through another resolver specified via --extra-resolvers.

    Note: Stainless will not pull transitive dependencies, so one has to specify all transitive dependencies explicitely via this option.

    Example: --extra-deps=ch.epfl.lara:stainless-algebra_2.12:0.1.2

  • --extra-resolvers=URL,...

    Specify additional resolvers to be used to fetch the dependencies specified via the --extra-deps option.

    Note: The full URL of the resolver must be used.

    Example: --extra-resolvers=https://oss.sonatype.org/content/repositories/snapshots/

    See the Coursier source code for the list of most common repositories URLs.

Additional Options (by component)

The following options relate to specific components in Stainless.


  • --strict-aritmetic

    Check arithmetic operations for unintended behaviour and overflows. Note that reasoning about bitvectors is sound even if this option is false, but in that case no warnings are generated for overflows and underflows because these have well-defined semantics in Scala.

  • --vc-cache

    Use a persistent cache mechanism to speed up verification; on by default.

  • --fail-early

    Aborts verification as soon as a VC cannot be proven to be correct.

  • --fail-invalid

    Aborts verification as soon as an invalid VC is found.


  • --ignore-posts

    Ignore postconditions during termination verification.

Unrolling Solver

  • --check-models

    Double-check counterexamples with the evaluator.

  • --feeling-lucky

    Use evaluator to find counterexamples early.

  • --unroll-assumptions

    Use unsat-assumptions to drive unrolling while remaining fair.

  • --silent-errors

    Don’t crash on errors, simply return Unknown.

  • --unroll-factor=n

    Speeds up unrolling by a factor n.

  • --model-finding=n

    Boosts model-finding capabilities by a factor n. This may come at the cost of proof construction.

  • --no-simplifications

    Disables program simplification heuristics.

CVC4 Solver

  • --solver:cvc4=<cvc4-opt>

    Pass extra command-line arguments to CVC4.


  • --codegen

    Use compiled evaluator instead of an interpreter.

  • --small-arrays

    Assume all arrays can fit into memory during compiled evaluation.

  • --instrument

    Instrument ADT field access during code generation.

  • --max-calls=n

    Bounds the total number of function call evaluations (before crashing).

  • --ignore-contracts

    Ignores function contracts during evaluation.

Tests generation

  • testgen-file=<file>

    Specifies the output file for the generated tests.

  • genc-testgen-includes=header1.h,header2,...

    Only applies for --genc-testgen. Indicates the headers to #include in the generated test file.

Configuration File

Stainless supports setting default values for command line options configuration files. To specify configuration file you can use the option `--config-file=FILE. The default is stainless.conf or .stainless.conf. The file should be a valid HOCON file.

For example, consider the config file containin the following lines:

vc-cache = false
debug = [verification, trees]
timeout = 5
check-models = true
print-ids = true

The file will translate to the following command line options:

--vc-cache=false --debug=verification,trees --timeout=5 --print-ids

Stainless searches for a configuration file recursively starting from the current directory and walking up the directory hierarchy. For example, if one runs stainless from /a/b/c and there is a config file in any of c, b or a, the first of those is going to be loaded.

Library Files

Purpose of library files

Stainless contains library source Scala files that define types and functions that are meant to be always available via import statements such as import stainless.lang._, import stainless.annotation._, import stainless.collection._, and so on. Many of these types have special treatment inside the extraction pipeline and will map directly to mathematical data types of the underlying SMT solvers. At build time, the build.sbt script computes the list of these files by traversing the frontends/library/ directory.

Changing the list of library files

To support further customization, if at run time stainless finds a file libfiles.txt in the current directory, it replaces the list of library files files with the list contained in this file, one file per line, with paths relative to the directory frontends/library/. For example, libfiles.txt may contain:


Shortening this list may reduce the startup time, but also cause Stainless to not work propertly, so using the --watch and --functions options is the first option to try.

For further customization by advanced users, please examine the build.sbt file.