Coding Standards Agent Skill

Coding Standards

TypeScript: No any

Never use any unless absolutely necessary — and that should be a final resort.

Process when you reach for any:

• Look for an existing type that fits. Most domains already have one.
• If no suitable type exists, define a proper one in the right location:
• Shared types → packages/shared/src/types.ts or relevant subdirectory
• SDK-specific types → packages/sandbox/src/clients/types.ts or the appropriate client file
• Container-specific types → under packages/sandbox-container/src/ with appropriate naming
• Use the new type everywhere it applies — don't leave one-off shapes scattered around.

This catches errors at compile time instead of runtime and keeps the codebase consistent.

Style: Uppercase Acronyms

When an acronym appears inside a camelCase or PascalCase identifier, keep it fully uppercase:

| ✅ Do | ❌ Don't |

| ----------------- | ----------------- |

| SandboxRPCAPI | SandboxRpcApi |

| containerURL | containerUrl |

| parseHTTPHeader | parseHttpHeader |

| getAPIKey | getApiKey |

Applies to all acronyms: API, URL, HTTP, RPC, SSE, SSH, DNS, ID, etc.

Exception: library-provided names keep their original casing (e.g. capnweb's RpcTarget stays RpcTarget).

Code Comments

Write comments for future readers, not for the current conversation.

Comments should describe the current state of the code. A developer reading the code months later won't have context about bugs that were fixed, conversations that happened, or earlier implementations.

Don't reference historical context

// ❌ Bad: references a bug the reader knows nothing about
// Uses character tracking to avoid the bug where indexOf('') returns wrong position

// ❌ Bad: implies something was wrong before
// Start the server with proper WebSocket typing

// ❌ Bad: "prevent" implies there was a problem to prevent
// Assign synchronously to prevent race conditions

Do describe current behavior and design intent

// ✅ Good: describes what the code does now
// Returns parsed events and any remaining unparsed content

// ✅ Good: explains design rationale without historical context
// Assigned synchronously so concurrent callers share the same connection attempt

// ✅ Good: explains a non-obvious implementation choice
// Uses IIFE to ensure promise exists before any await points

Smell test

If your comment contains "to avoid", "to fix", "to prevent", "instead of", or "properly" — reconsider whether you're describing current behavior or quietly referencing something that no longer exists. Rewrite to describe what the code does now and why this design was chosen.

API Design

When adding or modifying SDK methods:

• Use clear, descriptive names that indicate what the method does
• Validate inputs before passing to container APIs
• Provide helpful error messages with context (use the custom error classes in packages/shared/src/errors/)