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 jeremylongworth-source/AgentSkills --skill error-handling-contractsgit clone --depth 1 https://github.com/jeremylongworth-source/AgentSkillsWrote 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/jeremylongworth-source/agentskills/error-handling-contracts)<a href="https://agentmods.dev/skills/jeremylongworth-source/agentskills/error-handling-contracts"><img src="https://agentmods.dev/badge/skills/jeremylongworth-source/agentskills/error-handling-contracts/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/jeremylongworth-source/agentskills/error-handling-contracts"><img src="https://agentmods.dev/badge/skills/jeremylongworth-source/agentskills/error-handling-contracts.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 | $0.00049 | $0.00322 |
| Opus 5 | $0.00024 | $0.00161 |
| Sonnet 5 | $0.00010 | $0.00064 |
| Haiku 4.5 | $0.00005 | $0.00032 |
Grade A, and why
error-handling-contracts 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.
What it actually says
Error Handling Contracts
Core Workflow
- Identify clients, failure modes, transport, user-facing surfaces, and logging or observability needs.
- Define an error envelope with code, message, details, correlation ID, retry guidance, and documentation link where useful.
- Map domain failures to status codes or exception types.
- Separate client-safe messages from internal diagnostics.
- Specify retryability, idempotency, rate-limit behavior, and partial failure handling.
- Add tests and examples for expected error cases.
Safety Rules
- Do not expose stack traces, secrets, SQL, internal hosts, or sensitive user data in client-facing errors.
- Do not use errors to hide authorization decisions when explicit denial is required by product or compliance needs.
- Escalate error contracts for payments, auth, customer data, or public APIs.
Deliverable Shape
For error contracts, provide:
- Error envelope
- Status code or exception mapping
- Validation error format
- Retry and idempotency guidance
- Logging and correlation guidance
- Client-safe versus internal fields
- Examples
- Test cases
References
- Read
references/error-handling-contracts-checklist.mdwhen designing or reviewing backend error handling.
What ships with it
2 files 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 · 46 lines · 49 tokens per session scan A e4ea37f7a5ea
error-handling-contracts is a skill published in the GitHub repository jeremylongworth-source/AgentSkills (1 stars, last pushed 6d ago), licensed MIT. It adds 49 tokens to every session and 322 once invoked, about $0.0002 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 2026-09-03.
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