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 skills add oborchers/fractional-cto --skill error-handlinggit clone --depth 1 https://github.com/oborchers/fractional-ctoWrote 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/oborchers/fractional-cto/error-handling)<a href="https://agentmods.dev/skills/oborchers/fractional-cto/error-handling"><img src="https://agentmods.dev/badge/skills/oborchers/fractional-cto/error-handling/github.svg" alt="Measured on agentmods" height="20"></a>Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.
<a href="https://agentmods.dev/skills/oborchers/fractional-cto/error-handling"><img src="https://agentmods.dev/badge/skills/oborchers/fractional-cto/error-handling.svg" alt="Reviewed on agentmods" width="80" 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 5.1 | $0.00064 | $0.00841 |
| Opus 5.5 | $0.00026 | $0.00336 |
| Sonnet 5.5 | $0.00013 | $0.00168 |
| Haiku 4.5 | $0.00006 | $0.00084 |
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 5d 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 — 92 lines — stays where its author put it; the contents beside it link to each section on GitHub.
The Full Taxonomy of What Goes Wrong
Error handling in SaaS extends far beyond "something went wrong" modals. A production-ready application must account for every failure mode with specific, actionable responses.
Validation Errors
Surface inline, below the specific field, with red borders and actionable text.
Never use toasts for validation errors. Toasts stack, auto-dismiss before reading, and force users to hunt for the relevant field.
Permission Errors (403)
Must explain what the user can't do, why, and what they can do about it.
| Bad | Good |
|---|---|
| "Access denied" | "Only workspace admins can manage billing. Request access from @admin-name" |
| "Contact your administrator" | Show who has the required permission + a "Request Access" button |
| "Forbidden" | Suggest alternative actions the user CAN take |
Three response options to offer:
- Show who has the required permission
- Provide a "Request Access" button
- Suggest alternative actions
Session Expiry
Special care required. Jared Spool documented a case where a user completed a purchase, opened another tab, returned to find "Your session expired" — with no clarity on whether the purchase completed.
The principle: Always clearly communicate what was saved and what was lost.
Requirements:
- Show a warning modal with a countdown timer BEFORE expiration
- Include both "Continue Session" and "Log Out" buttons
- After auto-logout, display an inline notification on the login page explaining what happened
- Never leave ambiguity about what data was preserved
For additional session management guidance (adaptive MFA, auth flows), see the authentication skill.
Concurrent Edit Conflicts
The deepest technical-UX intersection. Figma's approach: model documents as property-level maps.
Resolution strategy:
- Two users changing different properties on the same object = no conflict
- Two users changing the same property = last-write-wins
- This is simpler than Operational Transformation or full CRDTs, and sufficient for most SaaS products
What ships with it
1 file beside SKILL.md in the same directory: the scripts, references and assets a skill reads on demand. Not counted in the per-session cost; read them before you install if any of them is executable.
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.
- 5d ago First seen · 92 lines · 64 tokens per session scan A a0ca35311358
error-handling is a skill published in the GitHub repository oborchers/fractional-cto (32 stars, last pushed 5d ago), licensed MIT. It adds 64 tokens to every session and 841 once invoked, about $0.0003 per session on Opus 5.5. 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 2026-10-13.
Other skills, from other repositories
html-ppt-zhangzara-block-frame
Rescuing a messy startup deck into a board-grade system — the diagnosis, the page grammar, and the rebuilt proof pages. Built as a decision-grade design craft deck for founders, exec presenter.
accesslint-scan
Audit a live page for accessibility issues, locate each WCAG violation precisely, and return a selector-grounded fix worklist without editing.
check
Reviews diffs, PRs, release readiness, and publishing follow-through. Use when asked to review, triage issues or PRs, or ship. Not for debugging root causes or prose.
health
Audits agent config, instruction drift, hooks or MCP, and AI maintainability. Use when Claude, Codex, or Pi setup looks wrong. Not for application bugs or PR review.
hunt
Finds root cause before any fix. Use when something errors, crashes, regresses, or used to work. Not for code review or new features.
think
Turns rough ideas into approved, decision-complete plans before coding. Use when planning architecture, judging whether to build, or writing a handoff. Not for bug fixes or small edits.