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 mpsuesser/pi-effect-harness --skill effect-concurrency-testinggit clone --depth 1 https://github.com/mpsuesser/pi-effect-harnessWrote 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/mpsuesser/pi-effect-harness/effect-concurrency-testing)<a href="https://agentmods.dev/skills/mpsuesser/pi-effect-harness/effect-concurrency-testing"><img src="https://agentmods.dev/badge/skills/mpsuesser/pi-effect-harness/effect-concurrency-testing/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/mpsuesser/pi-effect-harness/effect-concurrency-testing"><img src="https://agentmods.dev/badge/skills/mpsuesser/pi-effect-harness/effect-concurrency-testing.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 | $0.00043 | $0.03963 |
| Opus 5.5 | $0.00017 | $0.01585 |
| Sonnet 5.5 | $0.00009 | $0.00793 |
| Haiku 4.5 | $0.00004 | $0.00396 |
Grade A, and why
effect-concurrency-testing 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.
How it starts
The opening of the file, as written. The whole thing — 613 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Effect Concurrency Testing Skill
This skill provides patterns for testing Effect's concurrency primitives: fibers, latches, deferreds, PubSub, SubscriptionRef, and streams.
Core Principles
CRITICAL: Choose the correct coordination primitive based on what you need to synchronize.
| Need | Use |
|---|---|
| Simple fiber yield | Effect.yieldNow |
| Wait for subscriber ready | Deferred.make() + Deferred.await |
| Wait for stream element | Latch.make() + Stream.tap(() => latch.open) |
| Passive subscription registration | explicit readiness signal if possible; otherwise a tiny one-tick yield/sleep fallback |
| Time-dependent behavior | TestClock.adjust |
| Verify events published | PubSub.subscribe + PubSub.takeUpTo |
| Check fiber status | fiber.pollUnsafe() |
For Stream.fromPubSub subscription registration, prefer an explicit readiness signal when you control the stream. If the API offers no readiness hook and you only need registration to settle before publishing, a tiny Effect.yieldNow() or very short sleep is an acceptable last resort. Avoid broad polling or arbitrary delays.
Fiber Coordination Patterns
Effect.yieldNow - Simple Fiber Scheduling
Use Effect.yieldNow when you need to allow other fibers to execute. This is preferred over TestClock.adjust for non-time-dependent code.
import { it } from '@effect/vitest';
import { Effect, Exit, Fiber, Latch } from 'effect';
it.effect('fiber polling with yieldNow', () =>
Effect.gen(function* () {
const latch = yield* Latch.make();
const fiber = yield* latch.await.pipe(Effect.forkChild);
yield* Effect.yieldNow();
expect(fiber.pollUnsafe()).toBeUndefined();
yield* latch.open;
expect(yield* fiber.await).toEqual(Exit.void);
})
);
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 · 613 lines · 43 tokens per session scan A 5d2d5ea65913
effect-concurrency-testing is a skill published in the GitHub repository mpsuesser/pi-effect-harness (25 stars, last pushed 4mo ago), licensed MIT. It adds 43 tokens to every session and 3,963 once invoked, about $0.0002 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 2026-08-30.
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