A message template must conform to the specification. The rule raises an issue if the template string violates the template string grammar.

Why is this an issue?

A message template needs to comply with a set of rules. Logging provider parse the template and enrich log entries with the information found in the template. An unparsable message template leads to corrupted log entries and might result in a loss of information in the logs.

The rule covers the following logging frameworks:

How to fix it

Follow the syntax described on https://messagetemplates.org/.

Code examples

Noncompliant code example

logger.LogError("Login failed for {User", user);       // Noncompliant: Syntactically incorrect
logger.LogError("Login failed for {}", user);          // Noncompliant: Empty placeholder
logger.LogError("Login failed for {User-Name}", user); // Noncompliant: Only letters, numbers, and underscore are allowed for placeholders
logger.LogDebug("Retry attempt {Cnt,r}", cnt);         // Noncompliant: The alignment specifier must be numeric
logger.LogDebug("Retry attempt {Cnt:}", cnt);          // Noncompliant: Empty format specifier is not allowed

Compliant solution

logger.LogError("Login failed for {User}", user);
logger.LogError("Login failed for {User}", user);
logger.LogError("Login failed for {User_Name}", user);
logger.LogDebug("Retry attempt {Cnt,-5}", cnt);
logger.LogDebug("Retry attempt {Cnt:000}", cnt);

Resources

Documentation