`result += "..."` inside a loop. Strings are immutable, so each iteration allocates a new string and copies the old one: quadratic work for a linear job.
Each example shows the exact code shape the rule is looking for, then the smallest version that keeps the intent without hiding risk or adding noise.
var csv = "";
foreach (var row in rows)
{
csv += row.Id + "," + row.Name + "\n";
}
return csv;Deterministic brace-depth scan: tracks `for`, `foreach`, `while`, and `do` bodies and flags `name += ...` statements inside them that include a string literal.
var csv = new StringBuilder();
foreach (var row in rows)
{
csv.Append(row.Id).Append(',').Append(row.Name).Append('\n');
}
return csv.ToString();Append to a `StringBuilder` inside the loop and call `.ToString()` once afterwards, or use `string.Join` over the sequence.
Agents build output the way it reads, appending piece by piece, and do not switch to a builder when the append moves inside a loop.
ai-slop/csharp-string-concat-in-loop
ai-slop
Deterministic brace-depth scan: tracks `for`, `foreach`, `while`, and `do` bodies and flags `name += ...` statements inside them that include a string literal.
`+=` lines without a string literal (numeric accumulators, `s += name`), concatenation outside loop bodies, and loops whose body has no braces are not flagged.
Part of aislop's C# rule set. First-class C# support, including C#-specific AI-slop rules, arrived in aislop v0.14.1.