Diagnostics

Biome diagnostics explain errors, warnings, and other events in a structured format. They usually provide the context you need to understand and resolve an issue.

This page explains each part of a diagnostic and how to interpret it.

Diagnostic severity

A diagnostic’s severity determines how Biome reports it and can also affect the CLI. For example, an error causes the CLI to exit with a non-zero status code.

Fatal

Fatal diagnostics use red text and indicate that an unexpected error occurred inside Biome. Unlike error diagnostics, they include the fatal tag.

 FATAL  ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ✖ This diagnostic message is displayed in a color that reflects its severity.
  
  ⚠ Biome exited as this error could not be handled and resulted in a fatal error. Please report it if necessary.
  

Error

Error diagnostics use red text and should generally be addressed. The CLI will fail and exit when raised.

━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ✖ This diagnostic message is displayed in a color that reflects its severity.
  

Warning

Warning diagnostics use yellow text and should generally be addressed. By default, they do not cause the CLI to fail.

━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ⚠ This diagnostic message is displayed in a color that reflects its severity.
  

Information

Information diagnostics use green text. They provide useful context and do not cause the CLI to fail.

━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ℹ This diagnostic message is displayed in a color that reflects its severity.
  

Diagnostic tags

Tags are metadata attached to a diagnostic. They can change how clients display or handle it.

Verbose

Verbose diagnostics are hidden by default. To display them in the CLI, pass the --verbose option.

 VERBOSE  ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ✖ This diagnostic message is displayed in a color that reflects its severity.
  

Internal

Internal diagnostics indicate that an unexpected error occurred inside Biome. If you encounter one, please file a bug report on GitHub.

 INTERNAL  ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ✖ This diagnostic message is displayed in a color that reflects its severity.
  
  ⚠ This diagnostic was derived from an internal Biome error. Potential bug, please report it if necessary.
  

Fixable

Fixable diagnostics indicate that a fix is available. They are commonly used for lint diagnostics that offer a code action the user can review and apply.

 FIXABLE  ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ✖ This diagnostic message is displayed in a color that reflects its severity.
  

Deprecated

Deprecated diagnostics identify code or configuration that is obsolete and should no longer be used.

 DEPRECATED  ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ✖ This diagnostic message is displayed in a color that reflects its severity.
  

Diagnostic category

A diagnostic category is a identifier for the type of issue being reported. It appears in the diagnostic header and can identify a command, subsystem, or rule.

check ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ✖ This diagnostic message is displayed in a color that reflects its severity.
  

Some categories can also include a link. For example, lint/a11y/noAccessKey links to the documentation for that lint rule:

lint/a11y/noAccessKey ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ✖ This diagnostic message is displayed in a color that reflects its severity.
  

Diagnostic location

A diagnostic can include a file path, source code, and a highlighted range to show where an issue occurred. Each part is optional, so Biome displays whatever context is available.

A file path identifies which file the diagnostic refers to, even when no source code or exact position is available:

path/to/file.js ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ✖ This diagnostic message is displayed in a color that reflects its severity.
  

When source code and a highlighted range are available, Biome displays a code frame that points to the relevant text. This can appear without a file path, in which case the header does not include a line and column:

━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ✖ This diagnostic message is displayed in a color that reflects its severity.
  
  > 1 │ Some source code
      │      ^^^^^
  

When all three parts are available, Biome adds the line and column where the highlighted range begins to the file path:

path/to/file.txt:1:6 ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ✖ This diagnostic message is displayed in a color that reflects its severity.
  
  > 1 │ Some source code
      │      ^^^^^^
  

A highlighted range can cover multiple lines. In terminals embedded in many IDEs, you can click a location such as path/to/file.js:2:2 to open the file and place the cursor at the beginning of that range:

path/to/file.js:2:2 ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ✖ This diagnostic message is displayed in a color that reflects its severity.
  
    1 │ function name() {
  > 2 │ 	return 'lorem'
      │ 	^^^^^^^^^^^^^^
    3 │ }
  

Diagnostic advice

Diagnostics can include advice after the primary message. Advice can take several forms and is displayed by default. Verbose advice is displayed only when you pass the --verbose option.

━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ✖ This diagnostic message is displayed in a color that reflects its severity.
  
  ✖ An error message.
  
  ⚠ A warning message.
  
  ℹ An informational message.
  
  An unstyled message can introduce a command:
  
  $ biome command
  
  Messages can be grouped under a heading:
  
  Related information
  
    ℹ First message of a group.
    
    ℹ Second message of a group.
    
  Messages can also be displayed as a list:
  
  - First item
  - Second item
  
  A diff can show a suggested change:
  
  - Old·code
  + New·code
  
  A code frame can highlight a source range:
  
  > 1 │ Lorem
      │ ^^^
    2 │ Ipsum