projection-patterns

projection-patterns is a skill for Claude Code from wshobson/agents. It costs 36 tokens per session (542 once invoked), scanned A, original, MIT.

A guide to projections, which turn event streams into read models such as database tables, materialized views, caches, or search indexes. Event streams are ordered records of changes in a system.

In plain words
What is it for?
Use it to build CQRS read sides, rebuild models from past events, create dashboards and search indexes, and aggregate data across streams.
Why use it?
It helps make event-sourced data fast and useful to query without repeatedly processing the full event history.

Skill for Claude Code

Written for Claude Code: shipped in a Claude Code plugin.

Part of the backend-development plugin — 9 skills, 1 command, 5 agents shipped together

not rated 41krepo +534 today A scan Socket: passSnyk: passSkillSpector: pass 36 tokens original MIT

Good fit Use it to build CQRS read sides, rebuild models from past events, create dashboards and search indexes, and aggregate data across streams.

Compare 6 skills from other repositories ↓
Install with agentmods
npx agentmods add skills/wshobson/agents/projection-patterns
About the project

Agentic Plugin Marketplace is a collection of reusable plugins, agents, skills, commands, and rules for coding-agent tools including Claude Code, Codex CLI, Cursor, OpenCode, Antigravity CLI, and GitHub Copilot. It is for developers assembling agentic workflows across multiple harnesses from shared Markdown sources, and the catalogue entries are examples or subsets of those workflow components.

wshobson/agents · 41,158 stars · on GitHub · sethhobson.com

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 wshobson/agents --skill projection-patterns
Clone the repo
git clone --depth 1 https://github.com/wshobson/agents

Made for: Claude Code.

Or install backend-development, the plugin that ships this one along with the rest of its 9 skills, 1 command, 5 agents.

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 projection-patterns

README.md
[![agentmods](https://agentmods.dev/badge/skills/wshobson/agents/projection-patterns/github.svg)](https://agentmods.dev/skills/wshobson/agents/projection-patterns)
Your own site
<a href="https://agentmods.dev/skills/wshobson/agents/projection-patterns"><img src="https://agentmods.dev/badge/skills/wshobson/agents/projection-patterns/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 projection-patterns

Your own site · 80×15
<a href="https://agentmods.dev/skills/wshobson/agents/projection-patterns"><img src="https://agentmods.dev/badge/skills/wshobson/agents/projection-patterns.svg" alt="Reviewed on agentmods" width="80" height="20"></a>
Per session 36 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 542 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. Third-party audits
  • Socket pass 15 Sept 2026
  • Snyk pass 15 Sept 2026
  • NVIDIA SkillSpector pass 7 Sept 2026
How audits are shown
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 $0.00036 $0.00542
Opus 5.5 $0.00014 $0.00217
Sonnet 5.5 $0.00007 $0.00108
Haiku 4.5 $0.00004 $0.00054

Measured 1mo ago against content hash b05b06b24ea2, method: parsed. Prices are Anthropic first-party input rates as of 2026-10-07, from the pricing page.

Security

Grade A, and why

projection-patterns 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.

Origin

Copies of this mod

1 near-identical copy found in the catalogue:

plugins/backend-development/skills/projection-patterns/SKILL.md · 63 lines

How it starts

The opening of the file, as written. The whole thing — 63 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Projection Patterns

Comprehensive guide to building projections and read models for event-sourced systems.

When to Use This Skill

  • Building CQRS read models
  • Creating materialized views from events
  • Optimizing query performance
  • Implementing real-time dashboards
  • Building search indexes from events
  • Aggregating data across streams

Core Concepts

1. Projection Architecture

┌─────────────┐     ┌─────────────┐     ┌─────────────┐
│ Event Store │────►│ Projector   │────►│ Read Model  │
│             │     │             │     │ (Database)  │
│ ┌─────────┐ │     │ ┌─────────┐ │     │ ┌─────────┐ │
│ │ Events  │ │     │ │ Handler │ │     │ │ Tables  │ │
│ └─────────┘ │     │ │ Logic   │ │     │ │ Views   │ │
│             │     │ └─────────┘ │     │ │ Cache   │ │
└─────────────┘     └─────────────┘     └─────────────┘

2. Projection Types

Type Description Use Case
Live Real-time from subscription Current state queries
Catchup Process historical events Rebuilding read models
Persistent Stores checkpoint Resume after restart
Inline Same transaction as write Strong consistency

Templates and detailed worked examples

Full template library and detailed worked examples live in references/details.md. Read that file when you need the concrete templates.

Best Practices

Do's

  • Make projections idempotent - Safe to replay
  • Use transactions - For multi-table updates
  • Store checkpoints - Resume after failures
  • Monitor lag - Alert on projection delays
  • Plan for rebuilds - Design for reconstruction

Don'ts

  • Don't couple projections - Each is independent
  • Don't skip error handling - Log and alert on failures
  • Don't ignore ordering - Events must be processed in order
  • Don't over-normalize - Denormalize for query patterns

Read the full file on GitHub · 63 lines

Files

What ships with it

1 file 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. 1mo ago First seen · 63 lines · 36 tokens per session scan A b05b06b24ea2

Subscribe to this mod's changes

projection-patterns is a skill published in the GitHub repository wshobson/agents (41,158 stars, last pushed today), licensed MIT. It adds 36 tokens to every session and 542 once invoked, about $0.0001 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 2026-09-03.