Why Strict Pragma is Preferred Over Floating

Why Strict Pragma is Preferred Over Floating

Understanding Pragma in Solidity

In Solidity, a pragma is a crucial directive providing instructions to the compiler on how to process the source code. Known as "Pragmatic Information for Solidity," the pragma specifies the compiler version to be used when compiling a contract. This specification prompts the compiler to verify compatibility, generating an error if there's a mismatch, as even minor differences in compiler versions can affect contract behavior. For instance, a report states that over 60% of security issues in smart contracts stem from version incompatibility.

How Pragma Works in Solidity

The pragma directive is specific to each source file, meaning every Solidity file must define this directive to inform the compiler of the Solidity version used in the code, including imported libraries. Various methods exist to define the pragma version:

  • Floating Pragma: Indicates a range of acceptable compiler versions for compilation (e.g., pragma solidity ^0.8.0;).
  • Strict Pragma: Fixes the compiler version explicitly (e.g., pragma solidity 0.8.20;).
  • Range Pragma: Specifies a range of compiler versions (e.g., pragma solidity >=0.6.0 <0.8.20).

Why Use Strict Pragma?

Using a strict pragma is widely considered the best approach. Employing a floating pragma can lead to the inadvertent deployment of contracts with outdated or problematic compiler versions, introducing bugs and compromising the security of your smart contracts.

Vulnerabilities Associated With Floating Solidity Pragma

  1. Backward Incompatibility: Newer compiler versions might introduce breaking changes or deprecate certain features, causing existing code to behave differently or become invalid when compiled with a newer compiler version. This can lead to unexpected behavior or vulnerabilities in smart contracts.
  2. Unintentional Adoption of Experimental Features: Newer compiler versions may introduce experimental features or changes in language semantics. By using a floating pragma, developers may unintentionally adopt these features, potentially resulting in security implications if not fully understood or properly vetted.
  3. Security Patch Delays: While newer compiler versions may include security patches and improvements, relying on a floating pragma means that your code might not automatically benefit from these patches until you explicitly update the pragma directive and recompile your contracts.


For secure and reliable smart contracts, always prefer a strict pragma. This approach helps maintain consistency and avoids the pitfalls of floating pragmas, such as backward incompatibility and security patch delays.


1. What is a pragma in Solidity?

  • A pragma is a directive that provides instructions to the Solidity compiler on processing the source code, including specifying the compiler version.

2. What is the difference between strict and floating pragma?

  • A strict pragma specifies an exact compiler version, while a floating pragma allows a range of compiler versions.

3. Why is a strict pragma preferred?

  • Using a strict pragma avoids issues related to backward incompatibility, unintentional adoption of experimental features, and security patch delays.

4. How does floating pragma affect security?

  • Floating pragma can introduce vulnerabilities by compiling with outdated or problematic compiler versions, adopting experimental features, and delaying security patches.

5. Can I use a range pragma?

  • Yes, but it’s important to ensure the specified range does not introduce security risks or compatibility issues.

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