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 clubpay/ronykit --skill ddia-systemsgit clone --depth 1 https://github.com/clubpay/ronykitWrote 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/clubpay/ronykit/ddia-systems)<a href="https://agentmods.dev/skills/clubpay/ronykit/ddia-systems"><img src="https://agentmods.dev/badge/skills/clubpay/ronykit/ddia-systems/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/clubpay/ronykit/ddia-systems"><img src="https://agentmods.dev/badge/skills/clubpay/ronykit/ddia-systems.svg" alt="Reviewed on agentmods" width="80" height="20"></a>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 | $0.00128 | $0.04092 |
| Opus 5.5 | $0.00051 | $0.01637 |
| Sonnet 5.5 | $0.00026 | $0.00818 |
| Haiku 4.5 | $0.00013 | $0.00409 |
Grade A, and why
ddia-systems 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 23d 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 — 276 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Designing Data-Intensive Applications Framework
A principled approach to building reliable, scalable, and maintainable data systems. Apply these principles when choosing databases, designing schemas, architecting distributed systems, or reasoning about consistency and fault tolerance.
When to use
- Writing SDD §6 (data design): tables, keys, indexes, retention, partitioning.
- Choosing where state lives: Postgres (default), Redis, S3/MinIO, or a process-local cache.
- An app method does read-modify-write and could race with itself.
- A write must be safe under retries, duplicate delivery, or workflow replays.
- Queries degrade as a table grows, or replicas/caches serve stale data.
RonyKit mapping (scaffolded apps)
| Concern | RonyKit default | Read |
|---|---|---|
| System of record | Postgres + sqlc in internal/repo/v0, migrations in data/db/migrations |
MCP architecture/postgres-sqlc |
| Growing append-only tables | Postgres declarative RANGE partitioning with automated maintenance | MCP architecture/table-partitioning |
| Shared/distributed state, counters, limits | Redis via x/datasource.InitRedis; x/ratelimit on top |
MCP characteristics/redis |
| Hot read cache in one process | x/cache (Ristretto) — never shared state |
MCP characteristics/cache |
| Blobs/files | x/datasource S3/MinIO |
MCP packages/datasource |
| Retry-safe writes | Idempotency keys + unique constraints; upserts in sqlc | MCP characteristics/idempotent |
| Multi-step / cross-service consistency | flow workflows (sagas, compensation) instead of distributed transactions |
MCP characteristics/workflow |
Rules of thumb for feature modules:
- Let the database enforce invariants it can:
UNIQUE,CHECK,FOREIGN KEY, andNOT NULLbeat app-side checks that race. Map constraint violations torony/errsconflict errors in the repo adapter and cover them in the repo integration tests (go-testing). - Name the isolation you rely on. Postgres defaults to READ COMMITTED; a
check-then-write in
internal/appis a lost-update bug unless you useSELECT … FOR UPDATE, an atomicUPDATE … WHERE, optimistic versioning, or a unique constraint. - Index for the queries in
data/db/queries, not for every column; verify withEXPLAINon realistic volumes. - Cache is a derived view. Define its invalidation and staleness budget in the SDD before adding it.
- Vendor names below are illustrations, not recommendations. MongoDB, Cassandra, Kafka, Flink, and the rest show where each trade-off lives. In a RonyKit workspace, adding a datastore or broker beyond the defaults above is an SDD decision that needs the user's approval.
What ships with it
7 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.
- 23d ago First seen · 276 lines · 128 tokens per session scan A 57f7772dd98b
ddia-systems is a skill published in the GitHub repository clubpay/ronykit (38 stars, last pushed today), licensed BSD-3-Clause. It adds 128 tokens to every session and 4,092 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 2026-09-26.
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