# Source: https://docs.datadoghq.com/security/code_security/static_analysis/static_analysis_rules/csharp-best-practices/logger-constant-template.md

---
title: Use constant template when logging data
description: Datadog, the leading service for cloud-scale monitoring.
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  Docs > Datadog Security > Code Security > Static Code Analysis (SAST) > SAST
  Rules > Use constant template when logging data
---

# Use constant template when logging data

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## Metadata{% #metadata %}

**ID:** `csharp-best-practices/logger-constant-template`

**Language:** C#

**Severity:** Info

**Category:** Best Practices

## Description{% #description %}

Using interpolated strings (`$"..."`) or string concatenation forces the CLR to build a new string **every time** the log statement executes â even if the current log level is disabled (e.g., when logging at Debug in production). Prefer using constant templates when logging data.

## Non-Compliant Code Examples{% #non-compliant-code-examples %}

```csharp
_logger.LogInformation("User " + userId + " logged in");
```

```csharp
_logger.LogInformation($"User {userId} logged in at {timestamp}");
```

## Compliant Code Examples{% #compliant-code-examples %}

```csharp
// check log enablement before
if (_logger.IsEnabled(LogLevel.Debug)) {
    _logger.LogInformation("User " + userId + " logged in");
}
```

```csharp
_logger.LogInformation("User {UserId} logged in at {Timestamp}", userId, timestamp);
```
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