What is rust-error-handling?

A guide to handling failures in Rust with Result, Option, or panics, and to choosing between general and custom error types.

Use it when designing error types, propagating errors with ?, handling missing values, or deciding when a panic is justified.

It helps distinguish expected failures from programming bugs and gives callers enough information to respond appropriately.

rust-error-handling — Skill for Claude Code and Codex by heyAyushh

Install

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.

Any agent

npx skills add heyAyushh/stacc --skill error-handling

Clone the repo

git clone --depth 1 https://github.com/heyAyushh/stacc

Made for: Claude Code, Codex.

Wrote 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.

README.md

[![agentmods](https://agentmods.dev/badge/skills/heyayushh/stacc/error-handling/github.svg)](https://agentmods.dev/skills/heyayushh/stacc/error-handling)

Your own site

<a href="https://agentmods.dev/skills/heyayushh/stacc/error-handling"><img src="https://agentmods.dev/badge/skills/heyayushh/stacc/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.

Your own site · 80×15

<a href="https://agentmods.dev/skills/heyayushh/stacc/error-handling"><img src="https://agentmods.dev/badge/skills/heyayushh/stacc/error-handling.svg" alt="Reviewed on agentmods" width="80" height="20"></a>

Per session 39 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.

When invoked 805 The whole file, excluding the scripts and references it only reads on demand.

Security scan A 0 findings. A grade says what 26 rules found in the file — not that it is safe.

Origin original No closer match found in the catalogue.

Token cost

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	$0.00039	$0.00805
Opus 5	$0.00019	$0.00402
Sonnet 5	$0.00008	$0.00161
Haiku 4.5	$0.00004	$0.00081

Measured 9d ago against content hash e35a51da4f91, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-12, from the pricing page.

Security

Grade A, and why

rust-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 9d 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.

configs/stacks/rust/error-handling/SKILL.md · 114 lines

How it starts

The opening of the file, as written. The whole thing — 114 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Error Handling

Layer 1: Language Mechanics

Core Question

Is this failure expected or a bug?

Before choosing error handling strategy:

Can this fail in normal operation?
Who should handle this failure?
What context does the caller need?

Thinking Prompt

Before handling an error:

What kind of failure is this?
- Expected → Result<T, E>
- Absence normal → Option<T>
- Bug/invariant → panic!
- Unrecoverable → panic!
Who handles this?
- Caller → propagate with ?
- Current function → match/if-let
- User → friendly error message
- Programmer → panic with message
What context is needed?
- Type of error → thiserror variants
- Call chain → anyhow::Context
- Debug info → anyhow or tracing

Decision Flowchart

Is failure expected?
├─ Yes → Is absence the only "failure"?
│        ├─ Yes → Option<T>
│        └─ No → Result<T, E>
│                 ├─ Library → thiserror
│                 └─ Application → anyhow
└─ No → Is it a bug?
        ├─ Yes → panic!, assert!
        └─ No → Consider if really unrecoverable

Use ? → Need context?
├─ Yes → .context("message")
└─ No → Plain ?

Quick Reference

Pattern	When	Example
`Result<T, E>`	Recoverable error	`fn read() -> Result<String, io::Error>`
`Option<T>`	Absence is normal	`fn find() -> Option<&Item>`
`?`	Propagate error	`let data = file.read()?;`
`unwrap()`	Dev/test only	`config.get("key").unwrap()`
`expect()`	Invariant holds	`env.get("HOME").expect("HOME set")`
`panic!`	Unrecoverable	`panic!("critical failure")`

Library vs Application

Context	Error Crate	Why
Library	`thiserror`	Typed errors for consumers
Application	`anyhow`	Ergonomic error handling
Mixed	Both	thiserror at boundaries, anyhow internally

Common Mistakes

Mistake	Fix
`.unwrap()` in production	Use `?` or `match`
Type mismatch on `?`	Use `anyhow` or `impl From<E>`
Lost error context	Add `.context("what was happening")`
`Box<dyn Error>` everywhere	Use `thiserror` for typed errors

Read the full file on GitHub · 114 lines

Changes

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.

9d ago First seen · 114 lines · 39 tokens per session scan A e35a51da4f91

Subscribe to this mod's changes

rust-error-handling is a skill published in the GitHub repository heyAyushh/stacc (3 stars, last pushed 2mo ago), licensed MIT. It adds 39 tokens to every session and 805 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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