agentmods.dev

state-machine-design

state-machine-design is a skill for Claude Code, Codex from definite-d/agent-skills. It costs 173 tokens per session (5,395 once invoked), scanned A, original, MIT.

Guidance for modelling application logic, user interfaces, asynchronous operations, protocols, and business processes as connected states and events.

In plain words
What is it for?
Use it to design statecharts and implementation plans for systems such as UI flows, backend jobs, sessions, and protocols.
Why use it?
A state machine makes the allowed situations and transitions explicit, which helps clarify complex workflows.

Skill for Claude CodeCodex

Written for no agent in particular: nothing here depends on one.

not rated 2repo 7d ago A scan 173 tokens original MIT

Good fit Use it to design statecharts and implementation plans for systems such as UI flows, backend jobs, sessions, and protocols.

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Install with agentmods
npx agentmods add skills/definite-d/agent-skills/state-machine-design
View source ↗ definite-d/agent-skills
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 definite-d/agent-skills --skill state-machine-design
Clone the repo
git clone --depth 1 https://github.com/definite-d/agent-skills

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.

agentmods badge for state-machine-design

README.md
[![agentmods](https://agentmods.dev/badge/skills/definite-d/agent-skills/state-machine-design/github.svg)](https://agentmods.dev/skills/definite-d/agent-skills/state-machine-design)
Your own site
<a href="https://agentmods.dev/skills/definite-d/agent-skills/state-machine-design"><img src="https://agentmods.dev/badge/skills/definite-d/agent-skills/state-machine-design/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.

agentmods 80×15 button for state-machine-design

Your own site · 80×15
<a href="https://agentmods.dev/skills/definite-d/agent-skills/state-machine-design"><img src="https://agentmods.dev/badge/skills/definite-d/agent-skills/state-machine-design.svg" alt="Reviewed on agentmods" width="80" height="20"></a>
Per session 173 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 5,395 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.

ModelPer sessionOnce invoked
Fable 5.1 $0.00173 $0.05395
Opus 5 $0.00086 $0.02697
Sonnet 5 $0.00035 $0.01079
Haiku 4.5 $0.00017 $0.00539

Measured 8d ago against content hash ab8f19f90215, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-08, from the pricing page.

Security

Grade A, and why

state-machine-design 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 8d 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.

skills/state-machine-design/SKILL.md · 536 lines

How it starts

The opening of the file, as written. The whole thing — 536 lines — stays where its author put it; the contents beside it link to each section on GitHub.

State Machine Design Skill

This skill guides you through the complete process of designing a system using the state machine / statechart pattern — from requirements capture to a production-ready machine definition with implementation recommendations.

When to load additional references

  • New to state machines / fundamentals needed: read references/theory.md — formal definitions, variants (Moore/Mealy/HSM), UML notation, SCXML, core theorems, and patterns.
  • Implementation details (XState v5, Redux, Python, PostgreSQL/Redis persistence, Temporal, AWS Step Functions, SSE/WebSocket sync, testing): read references/implementation/INDEX.md first — it has a selection guide. Then load only the specific file(s) that match the target stack. Never load the whole folder.

Design Process

Phase 1 — Requirements Capture

Before drawing any states, extract from the user (or infer from context):

  1. Domain: What real-world entity or process are we modelling? (a UI component, a backend workflow, a protocol, a device, a user session?)
  2. Actors: Who/what triggers events? (user, timer, server, another machine)
  3. Events: What can happen? List all external signals and internal completions.
  4. Invariants: What must never be true simultaneously? (logged-in AND unauthenticated, loading AND has error)
  5. Success / terminal conditions: When is the machine "done"?
  6. Error paths: For every operation that can fail, how should failure be handled?
  7. Persistence tier: Does the machine need to survive restarts? (see Phase 4 — Source of Truth)
  8. Delivery semantics: Can any event arrive more than once? (user double-click, webhook retry, message-queue redelivery?) → mark those transitions as requiring idempotency guards.
  9. External dependencies: Does any state wait on a network call, worker, or hardware signal that could silently disappear? → those states require timeout / heartbeat exits (see Phase 3a).

Tip: Ask the user — "What are the things that can happen to this system, and what do they cause?" This naturally elicits events. Then ask "What does the system look like right now?" to elicit states. Finally ask "What external systems does this touch, and what happens if they go dark?" — this forces timeout and idempotency decisions up front.

Read the full file on GitHub · 536 lines

Files

What ships with it

15 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.

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.

  1. 8d ago First seen · 536 lines · 173 tokens per session scan A ab8f19f90215

Subscribe to this mod's changes

state-machine-design is a skill published in the GitHub repository definite-d/agent-skills (2 stars, last pushed 7d ago), licensed MIT. It adds 173 tokens to every session and 5,395 once invoked, about $0.0009 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 2026-08-31.

Planning
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