agentmods.dev

new-harness

new-harness is a skill for Claude Code from duyet/oma. It costs 45 tokens per session (423 once invoked), scanned A, original, Apache-2.0.

A scaffolding skill for adding a new harness, meaning the code that controls an agent’s model loop, to open-managed-agents.

In plain words
What is it for?
Use it to create and register harnesses for the default loop, ACP proxy, Flue, or another runtime.
Why use it?
It gives you the project’s current interface and registration steps, reducing mistakes when adding a new way to run the model.

Skill for Claude Code

Written for Claude Code: disable-model-invocation in frontmatter.

not rated 5 2d ago A scan 45 tokens original Apache-2.0
View the source file duyet/oma oma.duyet.net
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.

agentmods
npx agentmods add skills/duyet/oma/new-harness
Any agent
npx skills add duyet/oma --skill new-harness
Clone the repo
git clone --depth 1 https://github.com/duyet/oma

Made for: Claude Code.

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 new-harness

README.md
[![agentmods](https://agentmods.dev/badge/skills/duyet/oma/new-harness.svg)](https://agentmods.dev/skills/duyet/oma/new-harness)
Your own site
<a href="https://agentmods.dev/skills/duyet/oma/new-harness"><img src="https://agentmods.dev/badge/skills/duyet/oma/new-harness.svg" alt="Measured on agentmods" height="20"></a>
Per session 45 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 423 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. Scan, not verified.
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 $0.00045 $0.00423
Opus 5 $0.00023 $0.00211
Sonnet 5 $0.00009 $0.00085
Haiku 4.5 $0.00005 $0.00042

Measured 6d ago against content hash 75a3fb8db27b, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-06, from the pricing page.

Security

Grade A, and why

new-harness 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.

.claude/skills/new-harness/SKILL.md · 24 lines

What it actually says

Scaffold a new harness named $ARGUMENTS (the string an agent selects via harness: "<name>").

  1. Read the current contract first — open apps/agent/src/harness/interface.ts and use the live HarnessInterface, HarnessContext, and HarnessRuntime shapes. Do NOT assume a signature from memory; the interface evolves.

  2. Study a real implementation for the pattern:

    • apps/agent/src/harness/default-loop.ts (DefaultHarness) — drives its own streamText/generateText loop.
    • apps/agent/src/harness/acp-proxy-loop.ts / flue-loop.ts — meta-harnesses that hand the turn to an external runtime and make shouldCompact / compact / deriveModelContext deliberate no-ops.

  3. Create apps/agent/src/harness/<name>-loop.ts exporting a class that implements HarnessInterface. run(ctx) is required; only override the optional hooks (onSessionInit, shouldCompact, compact, deriveModelContext) where this harness must diverge from platform defaults. If you override deriveModelContext, keep its output byte-deterministic — the prompt cache invalidates on any prefix drift (see the interface comments).

  4. Register it in apps/agent/src/index.ts, next to the existing registerHarness(...) calls:

    import { <Name>Harness } from "./harness/<name>-loop";
registerHarness("<name>", () => new <Name>Harness());

  5. Add a unit test alongside the existing harness tests, then run /preflight.

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. 6d ago First seen · 24 lines · 45 tokens per session scan A 75a3fb8db27b

Subscribe to this mod's changes

new-harness is a skill published in the GitHub repository duyet/oma (5 stars, last pushed 2d ago), licensed Apache-2.0. It adds 45 tokens to every session and 423 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 2026-08-31.

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