Command Line 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 or off or no.

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 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 section.

  • --termination

    Runs termination analysis. Can be used along --verification.

  • --eval

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

  • --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.

  • --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 are:

    • solver (SMT solvers and their wrappers)
    • termination (Termination analysis)
    • timers (Timers, timer pools)
    • trees (Manipulation of trees)
    • verification (Verification)
  • --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.

Additional Options (by component)

The following options relate to specific components in Stainless.


  • --strict-aritmetic

    Check arithmetic operations for unintended behaviour and overflows.

  • --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.