event-driven

Event-driven architecture guidance covers systems where services communicate by sending messages or events instead of waiting for direct replies. It explains message brokers such as Kafka, RabbitMQ, and cloud queues, along with patterns for reliable delivery.

In plain words
What is it for?
Use it to design message topics and consumers, choose delivery rules, version event formats, handle failed messages, avoid inconsistent database writes, or build event-history and read-model systems.
Why use it?
It helps prevent lost, duplicated, or unprocessable messages when services work asynchronously or when one service is temporarily unavailable.

Skill for Claude CodeCodex

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.

agentmods
npx agentmods add skills/kid-sid/codex-spellbook/event-driven
Any agent
npx skills add kid-sid/codex-spellbook --skill event-driven
Clone the repo
git clone --depth 1 https://github.com/kid-sid/codex-spellbook

Made for: Claude Code, Codex.

Per session 42 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 3,353 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. Scan, not verified.
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 $0.00042 $0.03353
Opus 5 $0.00021 $0.01677
Sonnet 5 $0.00008 $0.00671
Haiku 4.5 $0.00004 $0.00335

Measured 2d ago against content hash d0d2d15b1c6f, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

event-driven 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 2d 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/event-driven/SKILL.md · 401 lines

How it starts

The opening of the file, as written. The whole thing — 401 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Event-Driven Architecture Patterns

Design and implementation patterns for reliable, scalable asynchronous systems using message brokers.

When to Activate

  • Decoupling services that currently call each other synchronously
  • Designing Kafka topics, partitions, or consumer group topology
  • Implementing event schemas with versioning and backward compatibility
  • Ensuring exactly-once or at-least-once delivery semantics
  • Setting up dead-letter queues and poison message handling
  • Implementing the outbox pattern to avoid dual-write problems
  • Building event sourcing or CQRS read-model projections

Core Concepts

Broker Comparison

Broker Retention Ordering Throughput Best For
Kafka Days–forever (log) Per partition Very high Event streaming, audit log, replay
RabbitMQ Until consumed Per queue High Task queues, RPC, routing flexibility
AWS SQS Up to 14 days None (FIFO available) High Simple queues, AWS-native workloads
Redis Streams Configurable Per stream High Low-latency, simple consumers
GCP Pub/Sub 7 days default None Very high GCP-native, push subscriptions

Delivery Semantics

Semantic How Tradeoff
At-least-once Commit offset only after processing Duplicates possible; consumer must be idempotent
At-most-once Commit before processing No duplicates; messages can be lost
Exactly-once Transactional producer + idempotent consumer Highest complexity; use outbox pattern instead

Default to at-least-once with idempotent consumers — it's simpler than exactly-once and eliminates loss.

Event Schema Design

Event Envelope

{
  "event_id": "01HXK4...",
  "event_type": "order.placed",
  "schema_version": "1.0",
  "occurred_at": "2025-06-01T12:00:00Z",
  "aggregate_id": "order-abc-123",
  "aggregate_type": "Order",
  "correlation_id": "req-xyz-456",
  "payload": {
    "customer_id": "cust-789",
    "total": "59.99",
    "currency": "USD",
    "items": [{ "sku": "WIDGET-01", "qty": 2, "unit_price": "29.99" }]
  }
}

Read the full file on GitHub · 401 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.

  1. 2d ago First seen · 401 lines · 42 tokens per session scan A d0d2d15b1c6f

Subscribe to this mod's changes

event-driven is a skill published in the GitHub repository kid-sid/codex-spellbook (21 stars, last pushed 3mo ago), licensed MIT. It adds 42 tokens to every session and 3,353 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 2026-08-30.

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