cratis-chronicle-projection

cratis-chronicle-projection is a skill for Claude Code, Codex from Cratis/AI. It costs 136 tokens per session (3,750 once invoked), scanned A, original, MIT.

A guide to making a Chronicle projection, which turns stored events into read-model data for queries. It explains attribute-based rules first and a code builder for shapes those rules cannot describe.

In plain words
What is it for?
Use it when populating an existing read model from events, selecting event sequences, mapping related data, or adding counters and child records.
Why use it?
It removes guesswork about mapping events to fields, keys, child records, counters, and nested data. It also helps avoid startup failures and prevents projections from doing work that belongs elsewhere.

Skill for Claude CodeCodex

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

Good fit Use it when populating an existing read model from events, selecting event sequences, mapping related data, or adding counters and child records.

Compare 6 skills from other repositories ↓
Install with agentmods
npx agentmods add skills/cratis/ai/cratis-chronicle-projection
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 Cratis/AI --skill cratis-chronicle-projection
Clone the repo
git clone --depth 1 https://github.com/Cratis/AI

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 cratis-chronicle-projection

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

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Your own site · 80×15
<a href="https://agentmods.dev/skills/cratis/ai/cratis-chronicle-projection"><img src="https://agentmods.dev/badge/skills/cratis/ai/cratis-chronicle-projection.svg" alt="Reviewed on agentmods" width="80" height="20"></a>
Per session 136 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 3,750 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 $0.00136 $0.03750
Opus 5.5 $0.00054 $0.01500
Sonnet 5.5 $0.00027 $0.00750
Haiku 4.5 $0.00014 $0.00375

Measured 8d ago against content hash ed1eade38dae, method: parsed. Prices are Anthropic first-party input rates as of 2026-10-07, from the pricing page.

Security

Grade A, and why

cratis-chronicle-projection 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.

.cratis/ai/skills/cratis-chronicle-projection/SKILL.md · 306 lines

How it starts

The opening of the file, as written. The whole thing — 306 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Chronicle projections

A projection consumes events and produces read-model state. It is pure: no side effects, and it never reads another read model. Prefer model-bound attributes on the read model; use the fluent builder when mappings need structure or the model should stay attribute-free; choose reducer code when state transitions read better as code. Follow the read-model style ladder: a self-reducing model is the new .NET reducer default, not a mandatory separate class. See reducers for that contract.

Verified product sources

Sources:

Package Purpose
Cratis.Chronicle Cratis.Chronicle.Projections, Cratis.Chronicle.Projections.ModelBound, Cratis.Chronicle.Keys, Cratis.Chronicle.EventSequences; self-model builder conflicts (Source/Clients/DotNET/ReadModels/ReadModelBuilderOwnership.cs, Reducers/SelfReducerMethods.cs)

Reverify product sources before claiming support for another version.

[ReadModel] and [Path] are Arc types (Cratis.Arc.Queries.ModelBound), not Chronicle types. A Chronicle read model that exists only as a projection target needs no [ReadModel] at all — that attribute is what gives it an Arc query surface.

What makes a type a model-bound projection

Chronicle treats a type as a model-bound projection when the class, its primary constructor parameters, or its public instance properties carry an [EventSequence] attribute or any projection annotation — except [Passive], which is deliberately excluded. [Passive] on its own therefore does not make a read model a projection; it changes how an existing projection is registered.

Model-bound projections — the default

Put the projection on the read model with attributes. No separate class.

using Cratis.Chronicle.Keys;
using Cratis.Chronicle.Projections.ModelBound;

[FromEvent<<EventName>>]
public record <ReadModelName>(
    [property: Key] <IdType> Id,
    <PropertyType> <PropertyName>);

Read the full file on GitHub · 306 lines

Files

What ships with it

5 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 Changed · +3 lines ed1eade38dae
  2. 10d ago Changed · -13 lines 3d75d93efa42
  3. 11d ago Changed · +34 lines cc2a17dec0e3
  4. 15d ago Changed · +9 lines · -14 tokens per session dee0884ef835
  5. 17d ago Changed · +13 lines 819719748d06
  6. 19d ago Changed · +14 lines d1b850df76e2
  7. 1mo ago Changed · +64 lines · +52 tokens per session 2396988e7d64
  8. 1mo ago Changed · +19 lines ddc939008c44
  9. 1mo ago First seen · 163 lines · 98 tokens per session scan A f09e9ca628a9

Subscribe to this mod's changes

cratis-chronicle-projection is a skill published in the GitHub repository Cratis/AI (4 stars, last pushed today), licensed MIT. It adds 136 tokens to every session and 3,750 once invoked, about $0.0005 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 2026-09-06.

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