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.
git clone --depth 1 https://github.com/PaulJPhilp/EffectPatternsWrote 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/rules/pauljphilp/effectpatterns/handle-your-first-error-with-effectfail-and-catchall)<a href="https://agentmods.dev/rules/pauljphilp/effectpatterns/handle-your-first-error-with-effectfail-and-catchall"><img src="https://agentmods.dev/badge/rules/pauljphilp/effectpatterns/handle-your-first-error-with-effectfail-and-catchall/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/rules/pauljphilp/effectpatterns/handle-your-first-error-with-effectfail-and-catchall"><img src="https://agentmods.dev/badge/rules/pauljphilp/effectpatterns/handle-your-first-error-with-effectfail-and-catchall.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 | $0.00244 | $0.00244 |
| Opus 5.5 | $0.00098 | $0.00098 |
| Sonnet 5.5 | $0.00049 | $0.00049 |
| Haiku 4.5 | $0.00024 | $0.00024 |
Grade A, and why
handle-your-first-error-with-effectfail-and-catchall 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 1mo 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
description: Handle errors with Effect.fail and catchAll. globs: "**/*.ts" alwaysApply: true
Handle Your First Error with Effect.fail and catchAll
Rule: Handle errors with Effect.fail and catchAll.
Example
import { Effect, pipe } from "effect";
class UserNotFound {
readonly _tag = "UserNotFound";
constructor(readonly id: string) {}
}
const findUser = (id: string) =>
id === "123"
? Effect.succeed({ id, name: "Alice" })
: Effect.fail(new UserNotFound(id));
const program = pipe(
findUser("456"),
Effect.catchTag("UserNotFound", (e) =>
Effect.succeed({ id: e.id, name: "Guest" })
),
Effect.map((user) => `Hello, ${user.name}!`)
);
const result = Effect.runSync(program);
console.log(result); // "Hello, Guest!"
Explanation:
Real programs fail. Effect makes failures explicit in the type system so you
can't forget to handle them. Unlike try/catch, Effect errors are tracked in
types.
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.
- 1mo ago First seen · 38 lines · 244 tokens per session scan A 59defb530658
handle-your-first-error-with-effectfail-and-catchall is a cursor rule published in the GitHub repository PaulJPhilp/EffectPatterns (807 stars, last pushed 4mo ago), licensed MIT. It adds 244 tokens to every session, about $0.0010 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 2026-09-03.
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