LowFile-scopeC# Plug & play

Use StringBuilder for string concatenation

Use StringBuilder for many concatenations in loops or when building large strings.

Why this matters

Avoids repeated allocations from immutable string concatenation.

Side-by-side examples engineers can pattern-match during review.

Avoid

var s = ""; foreach (var x in items) s += x;

Prefer

var sb = new StringBuilder(); foreach (var x in items) sb.Append(x); var s = sb.ToString();

Bad

s += part

Good

sb.Append(part)

From the same buckets as this rule.

Critical
Avoid Blocking Calls to Async Methods
Blocking async methods with `.Result` or `.Wait()` can cause deadlocks and prevent efficient asynchronous execution. Use `await` instead for proper async behavior.
concurrency-safetyperformance-efficiency
Critical
Fingerprint assets and cache immutably
All static JS/CSS/font/image files MUST use content-hashed filenames (e.g., app.9c1a7b.js) and be served with "Cache-Control: public, max-age=31536000, immutable". HTML and other non-fingerprinted documents MUST be served with "Cache-Control: no-cache" (or equivalent) to enable conditional revalidation.
web-static-assetscaching-strategy+2
Critical
No live network or DB in unit tests—use fakes/mocks
Unit tests must stub or fake external HTTP/DB calls; allow real I/O only in integration/e2e tests tagged accordingly.
testing-qualityperformance-efficiency+1