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 agentmods add skills/openclosed-org/axum-harness/backend-engineeringnpx skills add openclosed-org/axum-harness --skill backend-engineeringgit clone --depth 1 https://github.com/openclosed-org/axum-harnessWrote 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/openclosed-org/axum-harness/backend-engineering)<a href="https://agentmods.dev/skills/openclosed-org/axum-harness/backend-engineering"><img src="https://agentmods.dev/badge/skills/openclosed-org/axum-harness/backend-engineering.svg" alt="Measured on agentmods" 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 | $0.00065 | $0.00782 |
| Opus 5 | $0.00032 | $0.00391 |
| Sonnet 5 | $0.00013 | $0.00156 |
| Haiku 4.5 | $0.00006 | $0.00078 |
Grade A, and why
backend-engineering 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 6d 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 — 81 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Backend Engineering
Use this skill as the default quality lens for backend harness work.
Workflow skills guide judgment. Ownership skills still decide writable boundaries.
Objective
Keep the template small, explicit, typed, testable, and production-minded without pretending it is production-proven.
Prefer the smallest design that preserves:
- backend correctness
- hard service, protocol, server, worker, and platform boundaries
- topology-late growth
- executable evidence
- template-user simplicity
- agent resistance to drift
Decision Kernel
Before changing backend behavior, answer:
- What invariant must not be violated?
- Which boundary owns the violated or changed behavior?
- What is synchronous, asynchronous, durable, idempotent, replayable, or eventually consistent?
- What is the cheapest correct design that restores the invariant?
- What evidence can honestly be claimed after this change?
Boundary Rules
services/**are business capability libraries by default, not service processes.servers/**adapt protocols and compose services; handlers do not own domain logic.workers/**advance async state and must make retry, idempotency, checkpoint/replay, dedupe, and recovery explicit when touched.packages/contracts/**owns shared protocol shapes before external API or event changes land elsewhere.platform/model/**describes platform-level metadata and global defaults; service-local semantics stay inservices/<name>/model.yaml.- Generated artifacts are read-only; change sources and regenerate.
- Optional app shells and UI packages must not become backend-core prerequisites.
Quality Rules
- Represent important invariants in types, constructors, constraints, or final transaction boundaries.
- Keep expected failures typed and matchable; do not leak internal dependency details to clients.
- Retries for side-effecting work require durable idempotency or an explicit reason they are safe.
- Cross-boundary events require a clear atomic state mutation and publication story, usually outbox-driven.
- Async work must have bounded concurrency, cancellation/shutdown behavior, timeout or backpressure expectations, and observable failure paths when relevant.
- Do not add traits, managers, adapters, compatibility layers, or generic repositories unless they protect a real boundary or remove proven duplication.
- Prefer reference-module reuse over new structure, but do not copy business semantics blindly.
- Fix the smallest causal closed loop; avoid broad rewrites without an invariant-driven reason.
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.
- 6d ago First seen · 81 lines · 65 tokens per session scan A bedab4b4e34a
backend-engineering is a skill published in the GitHub repository openclosed-org/axum-harness (49 stars, last pushed 3mo ago), licensed Apache-2.0. It adds 65 tokens to every session and 782 once invoked, about $0.0003 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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