Getting it into your agent
One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.
npx agentmods add skills/komluk/scaffolding/error-handlingnpx skills add komluk/scaffolding --skill error-handlinggit clone --depth 1 https://github.com/komluk/scaffoldingWrote this? Show the measurements
A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.
[](https://agentmods.dev/skills/komluk/scaffolding/error-handling)<a href="https://agentmods.dev/skills/komluk/scaffolding/error-handling"><img src="https://agentmods.dev/badge/skills/komluk/scaffolding/error-handling.svg" alt="Measured on agentmods" height="20"></a>What it costs to keep this loaded
Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.
| Model | Per session | Once invoked |
|---|---|---|
| Fable 5 | $0.00061 | $0.01176 |
| Opus 5 | $0.00030 | $0.00588 |
| Sonnet 5 | $0.00012 | $0.00235 |
| Haiku 4.5 | $0.00006 | $0.00118 |
Grade A, and why
error-handling scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 4d ago.
A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.
Nothing flagged
None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.
How it starts
The opening of the file, as written. The whole thing — 192 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Error Handling Skill
Purpose
Standards for consistent error handling across frontend and backend layers (examples in React + Python).
Auto-Invoke Triggers
- Implementing exception handling
- Creating custom exceptions
- Handling API errors
- Implementing retry logic
- Designing user-facing error messages
Error Categories
| Category | HTTP Code | User Action | Log Level |
|---|---|---|---|
| Validation | 400 | Show field errors | WARN |
| Authentication | 401 | Redirect to login | WARN |
| Authorization | 403 | Show permission denied | WARN |
| NotFound | 404 | Show not found message | INFO |
| Conflict | 409 | Show conflict details | WARN |
| RateLimit | 429 | Show retry-after | WARN |
| ExternalService | 502 | Show fallback/retry option | ERROR |
| Internal | 500 | Show generic error | ERROR |
| Critical | 500 | Show maintenance page | CRITICAL |
Exception Hierarchy Design
Principles
- Create base
AppExceptionclass for all application errors - Extend with specific exception types per category
- Include: code, message, status code, details (optional)
- Never expose internal details to clients
Required Exception Types
ValidationException- Invalid input dataAuthenticationException- Auth token invalid/expiredAuthorizationException- User lacks permissionNotFoundException- Resource doesn't existConflictException- Resource state conflictRateLimitException- Too many requestsExternalServiceException- Third-party failure
Error Response Format
Standard Structure
{
"code": "ERROR_CODE",
"message": "Human-readable description",
"details": { "field": ["error1", "error2"] },
"correlationId": "abc-123"
}
Error Codes Convention
- Use SCREAMING_SNAKE_CASE
- Be specific:
USER_NOT_FOUNDnotNOT_FOUND - Group by domain:
AUTH_TOKEN_EXPIRED,AUTH_INVALID_CREDENTIALS
Frontend Error Handling
Principles
- Catch errors at API client level
- Transform to typed error objects
- Display user-friendly messages
- Log for debugging (not in production)
What this file has done since we first saw it
Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.
- 4d ago First seen · 192 lines · 61 tokens per session scan A d687bb5dbf52
error-handling is a skill published in the GitHub repository komluk/scaffolding (15 stars, last pushed 29d ago), licensed MIT. It adds 61 tokens to every session and 1,176 once invoked, about $0.0003 per session on Opus 5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.
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