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The first open-source Solidity static analysis framework. Slither provides automatic vulnerability and optimization detection, as well as auxiliary code base summaries.


Slither - Static Analyzer for Smart Contracts -

Modifications to the smart contract code are limited to the pre-deployment stage on Testnet or Mainnet. Once deployed, the code becomes immutable, and any vulnerabilities present can be exploited by malicious individuals, leading to substantial financial losses, as evidenced in past incidents. Consequently, thorough auditing of smart contracts prior to deployment is essential to ensure their security and reliability.

Enter Slither, a dynamic analysis framework designed specifically for smart contracts. Its primary purpose is to empower developers to swiftly identify vulnerabilities in their Solidity smart contract code within a matter of seconds. Beyond vulnerability detection, Slither can also serve as a valuable tool for code optimization and overall code review, enhancing the contract's robustness and efficiency.

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What is Slither?

Slither is an invaluable static analyzer designed for bolstering smart contract security. Developed by Trail Of Bits, it made its initial public debut in 2018.

This Python 3-based Solidity static analysis framework, as described by the company, employs a suite of vulnerability detectors, offers visual representations of contract details, and boasts an API that facilitates the creation of custom analyses. Its capabilities extend to identifying vulnerabilities, enhancing code comprehension, and streamlining the development of custom analyses.

Slither is known for its granular insight into smart contract code, offering remarkable flexibility to accommodate various applications. The framework currently serves the following purposes:

  1. Automated vulnerability detection: Slither can identify a wide range of smart contract bugs without requiring manual intervention or additional specifications.
  2. Automated optimization detection: It uncovers code optimizations that may be overlooked by the compiler.
  3. Code understanding: Slither presents concise summaries and displays vital contract information to aid in comprehending the codebase.
  4. Assisted code review: Users can interact with Slither through its API, enabling a more intuitive and efficient code review process.

This pioneering open-source static analysis framework for Solidity is a must-have for smart-contract developers, security experts, security audit companies, and academic researchers alike. Its versatile capabilities and user-friendly approach make it an indispensable tool in the quest for robust and secure smart contract development.


Prominent Features of Slither

Slither stands out with its exceptional performance and precision, rapidly detecting genuine vulnerabilities in a matter of seconds, all without requiring user intervention. Its hallmark trait lies in its impressive customizability, providing a comprehensive set of APIs that facilitate effortless inspection and analysis of Solidity code. Let's delve into some of the other remarkable features it offers:

  1. Low False Positives: Slither excels in detecting vulnerable Solidity code with minimal false positives, ensuring accurate and reliable results (refer to the list of "trophies").
  2. Error Localization: Not only does Slither identify vulnerabilities, but it also pinpoints the exact location in the source code where the error condition occurs, enabling developers to swiftly address the issues.
  3. Seamless Integration: Slither effortlessly integrates into continuous integration and Truffle builds, seamlessly becoming a part of the development workflow.
  4. Informative Reporting: With built-in "printers," Slither promptly generates comprehensive reports containing critical contract information, facilitating a comprehensive understanding of the contract's security status.
  5. Detector API: The framework offers a Detector API, enabling developers to craft custom analyses in Python, tailoring the tool to suit specific project requirements.
  6. Broad Solidity Compatibility: Slither has the capability to analyze contracts written with Solidity version greater than or equal to 0.4, accommodating a wide range of projects.
  7. Intermediate Representation (SlithIR): Slither's SlithIR enables developers to perform simple yet high-precision analyses, enhancing the depth and accuracy of the assessments.
  8. Robust Code Parsing: With an impressive parsing accuracy of 99.9% for all public Solidity code, Slither ensures that the analysis is conducted comprehensively and reliably.
  9. Swift Execution: Slither boasts an average execution time of less than 1 second per contract, ensuring efficient and time-saving assessments for large-scale projects.

These outstanding features make Slither an indispensable companion for developers seeking to fortify the security of their smart contracts, offering a powerful and customizable tool to ensure code integrity and enhance overall project robustness.


How Slither Functions:

Slither seamlessly integrates its core components with the vulnerability detection system to deliver a powerful and effective analysis tool. Although delving too deep into its technicalities is beyond the scope of this overview, a simplified diagram illustrates the process:

  • Input Processing: Slither takes the initial input in the form of the Solidity Abstract Syntax Tree (AST), which is generated by the Solidity compiler. This allows Slither to work effortlessly with popular frameworks like Truffle, Embark, and Dapp.
  • Information Generation: Upon receiving the AST, Slither proceeds to generate essential information, including the contract's inheritance graph, the control flow graph (CFG), and a comprehensive list of all expressions used in the contract.
  • Internal Representation: The code of the contract is then translated into SlithIR, an internal representation language specifically designed to facilitate precise and accurate analyses.
  • Pre-defined Analyses: Slither executes a series of pre-defined analyses, each designed to provide valuable insights to other modules. These analyses encompass a wide range of functionalities, such as computing data flow and identifying protected function calls, all contributing to enhanced overall analysis.

But how do we set Slither in motion to conduct these analyses?


Vulnerability Detection with Slither

Installing Slither

Slither requires Python 3.6+ and solc, the Solidity compiler.

pip install slither-analyzer


Seamless Integration with Continuous Integration

Slither boasts a user-friendly command-line interface, making it effortlessly accessible for developers. Running all of its detectors on a Solidity file is as simple as executing the following command: $ slither contract.sol

The beauty of Slither lies in its easy integration into your existing development process. No intricate configuration is required. By running Slither on each commit, you can ensure that every code change is thoroughly analyzed, safeguarding against the introduction of new bugs and vulnerabilities. This streamlined approach to continuous integration empowers developers to maintain the highest standard of code quality throughout the development lifecycle.


Detecting Security Vulnerabilities with Slither

In addition to its standard features, Slither offers an API that empowers developers to examine Solidity code using custom scripts. This API opens up several possibilities, allowing users to:

  • Identify Variable Modification: Utilize the API to pinpoint sections of code that have the capability to modify the value of a specific variable.
  • Analyze Conditional Logic: Isolate conditional logic statements that are influenced by the value of a particular variable, aiding in a more in-depth understanding of the contract's behavior under different conditions.
  • Explore Function Reachability: Through the API, developers can explore and identify other functions that become transitively reachable as a consequence of calling a specific function.

Other functions/features of Slither are listed below.

1. Contract summary printer

Gives a quick summary of the contract, showing the functions and their visibility:

2. Function summary printer

Shows useful information for each function, such as the state variables read and written, or the functions called:


3. Inheritance printer

Outputs a graph highlighting the inheritance dependencies of all the contracts:


4. Authorization printer
Shows what a user with privileges can do on the contract:


Slither can find real vulnerabilities in a few seconds with minimal or no user interaction. We employ it in most of our audits to strengthen security.


Concluding Remarks

Slither stands as a versatile and adaptable tool, offering a collection of robust, user-friendly analysis scripts written in Python, further complemented by its seamless integration with various Continuous Integration (CI) platforms.

Continuously evolving, Slither excels in detecting critical WARNINGs, particularly those related to Ether sending functions, while also effectively identifying all types of pseudo-bugs. Its primary focus, by design, is not on dynamic analysis, as this would compromise its core strengths—predictability, ease of use, and simplicity. By maintaining this approach, Slither ensures it remains a dependable and straightforward solution for smart contract security assessment.

In summary, Slither proves to be an indispensable asset for developers and security professionals, empowering them with a reliable and efficient tool to bolster the security of their Solidity smart contracts while maintaining a smooth and accessible user experience.

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