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Introduction to Custom Rules

What are Custom Rules?#

Custom rules are sets of code patterns and messages used by Sider's supported static code analyzers. You write custom rules to enforce your projects guidelines and share code-base knowledge. If the rules match a pattern in the code, they report a message.

Why it matters?#

Sharing code-base knowledge has many benefits to help improve projects, but sharing this information can be tedious and impractical. Creating custom rules provides a practical solution to embed project knowledge into your workflow, alerting your team of issues when they need it.

What are the tools?#

Sider currently supports 3 tools to analyze against custom rules.


Goodcheck is a tool that takes custom rules and matches the pattern with code. The rule's patterns are defined with regular expressions which allow it to work across all or specific text source code.

In this example, we look at maintaining consistent wording. When a user sees both “Sign in” and “Log in” within your web application, it may cause confusion or detract from the user experience.

rules:  - id: review.sider.wording.signin    pattern:      - token: Log in        case_sensitive: false      - token: Log out        case_sensitive: false    glob:      - "**/*.html.erb"      - "**/*.yml"    message: |      Please use "sign in" or "sign out".
      We use "sign in" instead of "log in" and "sign out" instead of "log out".      See the wording policy for details.    fail:      - "Log in"      - "Log out"    pass:      - "Sign in"      - "Sign out"

In this example, Goodcheck will analyze files with .html, .erb and .yml extensions for the pattern Log in or Log out. If the pattern is found, it would display the message: Please use "sign in" or "sign out".


Querly is a tool that understands Ruby syntax. It can take more complex patterns and find them in Ruby code.

In this example, assume there is an oauth_token method in your codebase. It is a credential and should not be leaked to logs. A developer adds a new option filtered. When filtered is true, the method returns an obfuscated token instead of a raw token so that you can write the obfuscated token on logs. Note that the behavior of oauth_token cannot be changed because the method is already used in the codebase.

rules:  - id: sider.auth_token    pattern: "_.oauth_token(!filtered: true)"    message: |      OAuth tokens are credential! Make sure they are filtered in logs.    justification:      - When you need an authentication for API calls    examples:      - before: "user.oauth_token[0...8] + '...'"        after: "user.oauth_token(filtered: true)"

With this rule, Querly would analyze Ruby source code files for any Ruby expression that includes the oauth_token method and checks if there is filtered: true as an argument. If there isn't, then a message will notify developers of the filtered option.


Phinder is a tool that understands PHP syntax. It can take complex PHP patterns and match them with PHP code.

Assume your service had an outage because of a PostCategory::import_records(associations) call. The method implements bulk insertion of given rows into a table. It is faster than inserting the rows one by one but may result in a deadlock, which is what caused the service outage. You can put links to the issue reports to help the developer to understand what they have to do to make the function call safe.

- id:  pattern: "_::import_records(_)"  message: |    `import_records(associations)` may block DB access
    Read the following reports and double check the method call does not block DB access.
    -    -

In this example, Phinder will match any PHP expression with a import_records class method. If there is a match, the message directs developers to the proper steps needed to make the function call safe.

Explainer Video#