Help is always welcome and there are plenty of options to contribute to Solidity.

In particular, we appreciate support in the following areas:

To get started, you can try Building from Source in order to familiarize yourself with the components of Solidity and the build process. Also, it may be useful to become well-versed at writing smart-contracts in Solidity.

Please note that this project is released with a Contributor Code of Conduct. By participating in this project — in the issues, pull requests, or Gitter channels — you agree to abide by its terms.

Team Calls

If you have issues or pull requests to discuss, or are interested in hearing what the team and contributors are working on, you can join our public team call:

  • Wednesdays at 3PM CET/CEST.

The call takes place on Jitsi.

How to Report Issues

To report an issue, please use the GitHub issues tracker. When reporting issues, please mention the following details:

  • Solidity version.

  • Source code (if applicable).

  • Operating system.

  • Steps to reproduce the issue.

  • Actual vs. expected behavior.

Reducing the source code that caused the issue to a bare minimum is always very helpful, and sometimes even clarifies a misunderstanding.

For technical discussions about language design, a post in the Solidity forum is the correct place (see Solidity Language Design).

Workflow for Pull Requests

In order to contribute, please fork off of the develop branch and make your changes there. Your commit messages should detail why you made your change in addition to what you did (unless it is a tiny change).

If you need to pull in any changes from develop after making your fork (for example, to resolve potential merge conflicts), please avoid using git merge and instead, git rebase your branch. This will help us review your change more easily.

Additionally, if you are writing a new feature, please ensure you add appropriate test cases under test/ (see below).

However, if you are making a larger change, please consult with the Solidity Development Gitter channel (different from the one mentioned above — this one is focused on compiler and language development instead of language usage) first.

New features and bugfixes should be added to the file: please follow the style of previous entries, when applicable.

Finally, please make sure you respect the coding style for this project. Also, even though we do CI testing, please test your code and ensure that it builds locally before submitting a pull request.

We highly recommend going through our review checklist before submitting the pull request. We thoroughly review every PR and will help you get it right, but there are many common problems that can be easily avoided, making the review much smoother.

Thank you for your help!

Running the Compiler Tests


For running all compiler tests you may want to optionally install a few dependencies (evmone, libz3).

On macOS systems, some of the testing scripts expect GNU coreutils to be installed. This can be easiest accomplished using Homebrew: brew install coreutils.

On Windows systems, make sure that you have a privilege to create symlinks, otherwise several tests may fail. Administrators should have that privilege, but you may also grant it to other users or enable Developer Mode.

Running the Tests

Solidity includes different types of tests, most of them bundled into the Boost C++ Test Framework application soltest. Running build/test/soltest or its wrapper scripts/ is sufficient for most changes.

The ./scripts/ script executes most Solidity tests automatically, including those bundled into the Boost C++ Test Framework application soltest (or its wrapper scripts/, as well as command-line tests and compilation tests.

The test system automatically tries to discover the location of the evmone for running the semantic tests.

The evmone library must be located in the deps or deps/lib directory relative to the current working directory, to its parent or its parent’s parent. Alternatively, an explicit location for the evmone shared object can be specified via the ETH_EVMONE environment variable.

evmone is needed mainly for running semantic and gas tests. If you do not have it installed, you can skip these tests by passing the --no-semantic-tests flag to scripts/

The evmone library should end with the file name extension .so on Linux, .dll on Windows systems and .dylib on macOS.

For running SMT tests, the libz3 library must be installed and locatable by cmake during compiler configure stage.

If the libz3 library is not installed on your system, you should disable the SMT tests by exporting SMT_FLAGS=--no-smt before running ./scripts/ or running ./scripts/ --no-smt. These tests are libsolidity/smtCheckerTests and libsolidity/smtCheckerTestsJSON.


To get a list of all unit tests run by Soltest, run ./build/test/soltest --list_content=HRF.

For quicker results you can run a subset of, or specific tests.

To run a subset of tests, you can use filters: ./scripts/ -t TestSuite/TestName, where TestName can be a wildcard *.

Or, for example, to run all the tests for the yul disambiguator: ./scripts/ -t "yulOptimizerTests/disambiguator/*" --no-smt.

./build/test/soltest --help has extensive help on all of the options available.

See especially:


Those working in a Windows environment wanting to run the above basic sets without libz3. Using Git Bash, you use: ./build/test/Release/soltest.exe -- --no-smt. If you are running this in plain Command Prompt, use .\build\test\Release\soltest.exe -- --no-smt.

If you want to debug using GDB, make sure you build differently than the “usual”. For example, you could run the following command in your build folder:

cmake -DCMAKE_BUILD_TYPE=Debug ..

This creates symbols so that when you debug a test using the --debug flag, you have access to functions and variables in which you can break or print with.

The CI runs additional tests (including solc-js and testing third party Solidity frameworks) that require compiling the Emscripten target.

Writing and Running Syntax Tests

Syntax tests check that the compiler generates the correct error messages for invalid code and properly accepts valid code. They are stored in individual files inside the tests/libsolidity/syntaxTests folder. These files must contain annotations, stating the expected result(s) of the respective test. The test suite compiles and checks them against the given expectations.

For example: ./test/libsolidity/syntaxTests/double_stateVariable_declaration.sol

contract test {
    uint256 variable;
    uint128 variable;
// ----
// DeclarationError: (36-52): Identifier already declared.

A syntax test must contain at least the contract under test itself, followed by the separator // ----. The comments that follow the separator are used to describe the expected compiler errors or warnings. The number range denotes the location in the source where the error occurred. If you want the contract to compile without any errors or warning you can leave out the separator and the comments that follow it.

In the above example, the state variable variable was declared twice, which is not allowed. This results in a DeclarationError stating that the identifier was already declared.

The isoltest tool is used for these tests and you can find it under ./build/test/tools/. It is an interactive tool which allows editing of failing contracts using your preferred text editor. Let’s try to break this test by removing the second declaration of variable:

contract test {
    uint256 variable;
// ----
// DeclarationError: (36-52): Identifier already declared.

Running ./build/test/tools/isoltest again results in a test failure:

syntaxTests/double_stateVariable_declaration.sol: FAIL
        contract test {
            uint256 variable;

    Expected result:
        DeclarationError: (36-52): Identifier already declared.
    Obtained result:

isoltest prints the expected result next to the obtained result, and also provides a way to edit, update or skip the current contract file, or quit the application.

It offers several options for failing tests:

  • edit: isoltest tries to open the contract in an editor so you can adjust it. It either uses the editor given on the command-line (as isoltest --editor /path/to/editor), in the environment variable EDITOR or just /usr/bin/editor (in that order).

  • update: Updates the expectations for contract under test. This updates the annotations by removing unmet expectations and adding missing expectations. The test is then run again.

  • skip: Skips the execution of this particular test.

  • quit: Quits isoltest.

All of these options apply to the current contract, except quit which stops the entire testing process.

Automatically updating the test above changes it to

contract test {
    uint256 variable;
// ----

and re-run the test. It now passes again:

Re-running test case...
syntaxTests/double_stateVariable_declaration.sol: OK


Choose a name for the contract file that explains what it tests, e.g. double_variable_declaration.sol. Do not put more than one contract into a single file, unless you are testing inheritance or cross-contract calls. Each file should test one aspect of your new feature.

Command-line Tests

Our suite of end-to-end command-line tests checks the behaviour of the compiler binary as a whole in various scenarios. These tests are located in test/cmdlineTests/, one per subdirectory, and can be executed using the script.

By default the script runs all available tests. You can also provide one or more file name patterns, in which case only the tests matching at least one pattern will be executed. It is also possible to exclude files matching a specific pattern by prefixing it with --exclude.

By default the script assumes that a solc binary is available inside the build/ subdirectory inside the working copy. If you build the compiler outside of the source tree, you can use the SOLIDITY_BUILD_DIR environment variable to specify a different location for the build directory.


export SOLIDITY_BUILD_DIR=~/solidity/build/
test/ "standard_*" "*_yul_*" --exclude "standard_yul_*"

The commands above will run tests from directories starting with test/cmdlineTests/standard_ and subdirectories of test/cmdlineTests/ that have _yul_ somewhere in the name, but no test whose name starts with standard_yul_ will be executed. It will also assume that the file solidity/build/solc/solc inside your home directory is the compiler binary (unless you are on Windows – then solidity/build/solc/Release/solc.exe).

There are several kinds of command-line tests:

  • Standard JSON test: contains at least an input.json file. In general may contain:

    • input.json: input file to be passed to the --standard-json option on the command line.

    • output.json: expected Standard JSON output.

    • args: extra command-line arguments passed to solc.

  • CLI test: contains at least an input.* file (other than input.json). In general may contain:

    • input.*: a single input file, whose name will be supplied to solc on the command line. Usually input.sol or input.yul.

    • args: extra command-line arguments passed to solc.

    • stdin: content to be passed to solc via standard input.

    • output: expected content of the standard output.

    • err: expected content of the standard error output.

    • exit: expected exit code. If not provided, zero is expected.

  • Script test: contains a test.* file. In general may contain:

    • test.*: a single script to run, usually or The script must be executable.

Running the Fuzzer via AFL

Fuzzing is a technique that runs programs on more or less random inputs to find exceptional execution states (segmentation faults, exceptions, etc). Modern fuzzers are clever and run a directed search inside the input. We have a specialized binary called solfuzzer which takes source code as input and fails whenever it encounters an internal compiler error, segmentation fault or similar, but does not fail if e.g., the code contains an error. This way, fuzzing tools can find internal problems in the compiler.

We mainly use AFL for fuzzing. You need to download and install the AFL packages from your repositories (afl, afl-clang) or build them manually. Next, build Solidity (or just the solfuzzer binary) with AFL as your compiler:

cd build
# if needed
make clean
cmake .. -DCMAKE_C_COMPILER=path/to/afl-gcc -DCMAKE_CXX_COMPILER=path/to/afl-g++
make solfuzzer

At this stage, you should be able to see a message similar to the following:

Scanning dependencies of target solfuzzer
[ 98%] Building CXX object test/tools/CMakeFiles/solfuzzer.dir/fuzzer.cpp.o
afl-cc 2.52b by <>
afl-as 2.52b by <>
[+] Instrumented 1949 locations (64-bit, non-hardened mode, ratio 100%).
[100%] Linking CXX executable solfuzzer

If the instrumentation messages did not appear, try switching the cmake flags pointing to AFL’s clang binaries:

# if previously failed
make clean
cmake .. -DCMAKE_C_COMPILER=path/to/afl-clang -DCMAKE_CXX_COMPILER=path/to/afl-clang++
make solfuzzer

Otherwise, upon execution the fuzzer halts with an error saying binary is not instrumented:

afl-fuzz 2.52b by <>
... (truncated messages)
[*] Validating target binary...

[-] Looks like the target binary is not instrumented! The fuzzer depends on
    compile-time instrumentation to isolate interesting test cases while
    mutating the input data. For more information, and for tips on how to
    instrument binaries, please see /usr/share/doc/afl-doc/docs/README.

    When source code is not available, you may be able to leverage QEMU
    mode support. Consult the README for tips on how to enable this.
    (It is also possible to use afl-fuzz as a traditional, "dumb" fuzzer.
    For that, you can use the -n option - but expect much worse results.)

[-] PROGRAM ABORT : No instrumentation detected
         Location : check_binary(), afl-fuzz.c:6920

Next, you need some example source files. This makes it much easier for the fuzzer to find errors. You can either copy some files from the syntax tests or extract test files from the documentation or the other tests:

mkdir /tmp/test_cases
cd /tmp/test_cases
# extract from tests:
path/to/solidity/scripts/ path/to/solidity/test/libsolidity/SolidityEndToEndTest.cpp
# extract from documentation:
path/to/solidity/scripts/ path/to/solidity/docs

The AFL documentation states that the corpus (the initial input files) should not be too large. The files themselves should not be larger than 1 kB and there should be at most one input file per functionality, so better start with a small number of. There is also a tool called afl-cmin that can trim input files that result in similar behavior of the binary.

Now run the fuzzer (the -m extends the size of memory to 60 MB):

afl-fuzz -m 60 -i /tmp/test_cases -o /tmp/fuzzer_reports -- /path/to/solfuzzer

The fuzzer creates source files that lead to failures in /tmp/fuzzer_reports. Often it finds many similar source files that produce the same error. You can use the tool scripts/ to filter out the unique errors.


Whiskers is a string templating system similar to Mustache. It is used by the compiler in various places to aid readability, and thus maintainability and verifiability, of the code.

The syntax comes with a substantial difference to Mustache. The template markers {{ and }} are replaced by < and > in order to aid parsing and avoid conflicts with Yul (The symbols < and > are invalid in inline assembly, while { and } are used to delimit blocks). Another limitation is that lists are only resolved one depth and they do not recurse. This may change in the future.

A rough specification is the following:

Any occurrence of <name> is replaced by the string-value of the supplied variable name without any escaping and without iterated replacements. An area can be delimited by <#name>...</name>. It is replaced by as many concatenations of its contents as there were sets of variables supplied to the template system, each time replacing any <inner> items by their respective value. Top-level variables can also be used inside such areas.

There are also conditionals of the form <?name>...<!name>...</name>, where template replacements continue recursively either in the first or the second segment depending on the value of the boolean parameter name. If <?+name>...<!+name>...</+name> is used, then the check is whether the string parameter name is non-empty.

Documentation Style Guide

In the following section you find style recommendations specifically focusing on documentation contributions to Solidity.

English Language

Use International English, unless using project or brand names. Try to reduce the usage of local slang and references, making your language as clear to all readers as possible. Below are some references to help:


While the official Solidity documentation is written in English, there are community contributed Translations in other languages available. Please refer to the translation guide for information on how to contribute to the community translations.

Title Case for Headings

Use title case for headings. This means capitalise all principal words in titles, but not articles, conjunctions, and prepositions unless they start the title.

For example, the following are all correct:

  • Title Case for Headings.

  • For Headings Use Title Case.

  • Local and State Variable Names.

  • Order of Layout.

Expand Contractions

Use expanded contractions for words, for example:

  • “Do not” instead of “Don’t”.

  • “Can not” instead of “Can’t”.

Active and Passive Voice

Active voice is typically recommended for tutorial style documentation as it helps the reader understand who or what is performing a task. However, as the Solidity documentation is a mixture of tutorials and reference content, passive voice is sometimes more applicable.

As a summary:

  • Use passive voice for technical reference, for example language definition and internals of the Ethereum VM.

  • Use active voice when describing recommendations on how to apply an aspect of Solidity.

For example, the below is in passive voice as it specifies an aspect of Solidity:

Functions can be declared pure in which case they promise not to read from or modify the state.

For example, the below is in active voice as it discusses an application of Solidity:

When invoking the compiler, you can specify how to discover the first element of a path, and also path prefix remappings.

Common Terms

  • “Function parameters” and “return variables”, not input and output parameters.

Code Examples

A CI process tests all code block formatted code examples that begin with pragma solidity, contract, library or interface using the ./test/ script when you create a PR. If you are adding new code examples, ensure they work and pass tests before creating the PR.

Ensure that all code examples begin with a pragma version that spans the largest where the contract code is valid. For example pragma solidity >=0.4.0 <0.9.0;.

Running Documentation Tests

Make sure your contributions pass our documentation tests by running ./docs/ that installs dependencies needed for documentation and checks for any problems such as broken links or syntax issues.

Solidity Language Design

To actively get involved in the language design process and to share your ideas concerning the future of Solidity, please join the Solidity forum.

The Solidity forum serves as the place to propose and discuss new language features and their implementation in the early stages of ideation or modifications of existing features.

As soon as proposals get more tangible, their implementation will also be discussed in the Solidity GitHub repository in the form of issues.

In addition to the forum and issue discussions, we regularly host language design discussion calls in which selected topics, issues or feature implementations are debated in detail. The invitation to those calls is shared via the forum.

We are also sharing feedback surveys and other content that is relevant to language design in the forum.

If you want to know where the team is standing in terms or implementing new features, you can follow the implementation status in the Solidity GitHub project. Issues in the design backlog need further specification and will either be discussed in a language design call or in a regular team call. You can see the upcoming changes for the next breaking release by changing from the default branch (develop) to the breaking branch.

For ad-hoc cases and questions, you can reach out to us via the Solidity-dev Gitter channel — a dedicated chatroom for conversations around the Solidity compiler and language development.

We are happy to hear your thoughts on how we can improve the language design process to be even more collaborative and transparent.