How do I install the Fict Best Practices skill?

Run npx skillmds@latest add marmelab/fict-best-practices in your terminal (requires Node.js), paste this page's agent-chat prompt into Claude, Cursor, or any MCP-connected agent, or download the SKILL.md file and copy it into your agent's skills directory.

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This skill is tagged as working with Claude Code, Claude.ai, OpenAI Codex. SKILL.md is an open format, so most agents that read a skills directory can load it too.

Is Fict Best Practices free to use?

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Who published Fict Best Practices?

marmelab (@marmelab) published this skill. Their other Agent Skills are listed on their SkillMD profile.

Fict Best Practices by marmelab — Agent Skill

Name: Fict Best Practices
Author: marmelab

Fict Best Practices

Fict compiler and runtime engineering guide for correctness and reliability. Use when implementing or reviewing Fict compiler transforms, runtime reactivity behavior, SSR/resume flow, devtools/playground integration, or release CI gates in Fict repositories.

marmelab Updated Sep 17, 2026

File contents

Fict Compiler and Runtime Best Practices

Production-focused guidance for engineering tasks across Fict compiler, runtime, SSR, devtools, and release workflows. Rules are optimized for AI agents doing code changes and reviews under correctness and regression-risk constraints.

Rule Categories by Priority

Priority	Category	Impact	Prefix
1	Compiler Guarantees	CRITICAL	`compiler-`
2	Reactivity Semantics	CRITICAL	`reactivity-`
3	Runtime Safety and Performance	HIGH	`runtime-`
4	SSR and Resume Stability	HIGH	`ssr-`
5	Tooling and DX Boundaries	MEDIUM	`tooling-`
6	Verification and Release Discipline	CRITICAL	`quality-`

Quick Reference

1. Compiler Guarantees (CRITICAL)

compiler-strict-guarantee-ci - Enforce fail-closed guarantee mode in CI
compiler-macro-placement-top-level - Keep macros at top-level component or hook scope
compiler-fail-closed-diagnostics - Treat fallback diagnostics as blockers

2. Reactivity Semantics (CRITICAL)

reactivity-derived-values - Rely on compiler-derived memoization and avoid stale snapshots
reactivity-no-state-escape - Prevent state lifetime escape outside owning scope
reactivity-props-shaping - Keep props/reactive object shaping analyzable

3. Runtime Safety and Performance (HIGH)

runtime-shared-state-primitives - Use $store/createSignal for shared state boundaries
runtime-effect-cleanup - Always return cleanup for subscriptions and async side effects
runtime-no-side-effects-in-memo - Keep memo bodies pure and move effects to $effect

4. SSR and Resume Stability (HIGH)

ssr-resource-keying - Key resources and align Suspense boundaries with async ownership
ssr-resume-snapshot-contract - Preserve snapshot schema and loader failure semantics

5. Tooling and DX Boundaries (MEDIUM)

tooling-devtools-dev-only - Keep devtools instrumentation development-only
tooling-playground-runtime-isolation - Isolate playground features from production runtime code paths

6. Verification and Release Discipline (CRITICAL)

quality-regression-tests-for-bugs - Add minimal regression tests for every fixed defect
quality-release-gates - Run compiler/runtime gates before merge or release

How to Use

Read rule files in rules/ for detailed explanations and bad/good examples. Use AGENTS.md when you want a single compiled document with all rules.

Full Compiled Document

AGENTS.md

---name: fict-best-practicesdescription: Fict compiler and runtime engineering guide for correctness and reliability. Use when implementing or reviewing Fict compiler transforms, runtime reactivity behavior, SSR/resume flow, devtools/playground integration, or release CI gates in Fict repositories.---# Fict Compiler and Runtime Best PracticesProduction-focused guidance for engineering tasks across Fict compiler, runtime,SSR, devtools, and release workflows. Rules are optimized for AI agents doingcode changes and reviews under correctness and regression-risk constraints.## Rule Categories by Priority| Priority | Category | Impact | Prefix || -------- | ----------------------------------- | -------- | ------------- || 1 | Compiler Guarantees | CRITICAL | `compiler-` || 2 | Reactivity Semantics | CRITICAL | `reactivity-` || 3 | Runtime Safety and Performance | HIGH | `runtime-` || 4 | SSR and Resume Stability | HIGH | `ssr-` || 5 | Tooling and DX Boundaries | MEDIUM | `tooling-` || 6 | Verification and Release Discipline | CRITICAL | `quality-` |## Quick Reference### 1. Compiler Guarantees (CRITICAL)- `compiler-strict-guarantee-ci` - Enforce fail-closed guarantee mode in CI- `compiler-macro-placement-top-level` - Keep macros at top-level component or hook scope- `compiler-fail-closed-diagnostics` - Treat fallback diagnostics as blockers### 2. Reactivity Semantics (CRITICAL)- `reactivity-derived-values` - Rely on compiler-derived memoization and avoid stale snapshots- `reactivity-no-state-escape` - Prevent state lifetime escape outside owning scope- `reactivity-props-shaping` - Keep props/reactive object shaping analyzable### 3. Runtime Safety and Performance (HIGH)- `runtime-shared-state-primitives` - Use `$store`/`createSignal` for shared state boundaries- `runtime-effect-cleanup` - Always return cleanup for subscriptions and async side effects- `runtime-no-side-effects-in-memo` - Keep memo bodies pure and move effects to `$effect`### 4. SSR and Resume Stability (HIGH)- `ssr-resource-keying` - Key resources and align Suspense boundaries with async ownership- `ssr-resume-snapshot-contract` - Preserve snapshot schema and loader failure semantics### 5. Tooling and DX Boundaries (MEDIUM)- `tooling-devtools-dev-only` - Keep devtools instrumentation development-only- `tooling-playground-runtime-isolation` - Isolate playground features from production runtime code paths### 6. Verification and Release Discipline (CRITICAL)- `quality-regression-tests-for-bugs` - Add minimal regression tests for every fixed defect- `quality-release-gates` - Run compiler/runtime gates before merge or release## How to UseRead rule files in `rules/` for detailed explanations and bad/good examples.Use `AGENTS.md` when you want a single compiled document with all rules.## Full Compiled Document`AGENTS.md`

Frequently asked questions