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 aj-geddes/useful-ai-prompts --skill event-sourcinggit clone --depth 1 https://github.com/aj-geddes/useful-ai-promptsWrote 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/aj-geddes/useful-ai-prompts/event-sourcing)<a href="https://agentmods.dev/skills/aj-geddes/useful-ai-prompts/event-sourcing"><img src="https://agentmods.dev/badge/skills/aj-geddes/useful-ai-prompts/event-sourcing/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/aj-geddes/useful-ai-prompts/event-sourcing"><img src="https://agentmods.dev/badge/skills/aj-geddes/useful-ai-prompts/event-sourcing.svg" alt="Reviewed on agentmods" width="80" height="20"></a>- Socket pass
- Snyk pass
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 | $0.00035 | $0.00544 |
| Opus 5 | $0.00017 | $0.00272 |
| Sonnet 5 | $0.00007 | $0.00109 |
| Haiku 4.5 | $0.00003 | $0.00054 |
Grade A, and why
event-sourcing 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 9d 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 — 99 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Event Sourcing
Table of Contents
Overview
Store state changes as a sequence of events rather than the current state, enabling temporal queries, audit trails, and event replay.
When to Use
- Audit trail requirements
- Temporal queries (state at any point in time)
- Event-driven microservices
- CQRS implementations
- Financial systems
- Complex domain models
- Debugging and analysis
- Compliance and regulation
Quick Start
Minimal working example:
interface DomainEvent {
id: string;
aggregateId: string;
aggregateType: string;
eventType: string;
data: any;
metadata: {
userId?: string;
timestamp: number;
version: number;
};
}
interface Aggregate {
id: string;
version: number;
}
class EventStore {
private events: DomainEvent[] = [];
async appendEvents(
aggregateId: string,
expectedVersion: number,
events: Omit<DomainEvent, "id" | "metadata">[],
// ... (see reference guides for full implementation)
Reference Guides
Detailed implementations in the references/ directory:
| Guide | Contents |
|---|---|
| Event Store (TypeScript) | Event Store (TypeScript) |
| Projections (Read Models) | Projections (Read Models) |
| Event Store with PostgreSQL | Event Store with PostgreSQL |
| Snapshots for Performance | Snapshots for Performance |
Best Practices
✅ DO
- Store events immutably
- Version your events
- Use optimistic concurrency
- Create snapshots for performance
- Use projections for queries
- Keep events small and focused
- Include metadata (timestamp, user, etc.)
- Handle event versioning/migration
❌ DON'T
- Mutate past events
- Store current state only
- Skip concurrency checks
- Query event store for reads
- Make events too large
- Forget about event schema evolution
What ships with it
6 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.
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.
- 9d ago First seen · 99 lines · 35 tokens per session scan A cb90bbefd23d
event-sourcing is a skill published in the GitHub repository aj-geddes/useful-ai-prompts (338 stars, last pushed 6mo ago), licensed MIT. It adds 35 tokens to every session and 544 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 2026-09-03.
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