nexus-eval-harness

nexus-eval-harness is a skill for Claude Code, Codex from cbruyndoncx/ThirdBrAIn-MCPSERVERS-IQ. It costs 96 tokens per session (1,022 once invoked), scanned A, original, no licence file.

A guide for working on the Nexus language-model evaluation harness, the test system that checks how well an AI behaves. It covers scenarios, evaluation settings, execution, checks, reports, and diagnosing confusing results.

In plain words
What is it for?
Use it to create or repair evaluation scenarios, write evaluation settings, change runners or checks, adjust reports, and explain unusual runs.
Why use it?
It helps when an AI evaluation is incorrect, fails completely, produces no output, or reports numbers that do not agree. It keeps investigation focused on the harness and its test inputs.

Skill for Claude CodeCodex

Written for Claude Code and Codex: installed under .claude/, but also agents/openai.yaml present.

Good fit Use it to create or repair evaluation scenarios, write evaluation settings, change runners or checks, adjust reports, and explain unusual runs.

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Install with agentmods
npx agentmods add skills/cbruyndoncx/thirdbrain-mcpservers-iq/nexus-eval-harness
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 cbruyndoncx/ThirdBrAIn-MCPSERVERS-IQ --skill nexus-eval-harness
Clone the repo
git clone --depth 1 https://github.com/cbruyndoncx/ThirdBrAIn-MCPSERVERS-IQ

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 nexus-eval-harness

README.md
[![agentmods](https://agentmods.dev/badge/skills/cbruyndoncx/thirdbrain-mcpservers-iq/nexus-eval-harness/github.svg)](https://agentmods.dev/skills/cbruyndoncx/thirdbrain-mcpservers-iq/nexus-eval-harness)
Your own site
<a href="https://agentmods.dev/skills/cbruyndoncx/thirdbrain-mcpservers-iq/nexus-eval-harness"><img src="https://agentmods.dev/badge/skills/cbruyndoncx/thirdbrain-mcpservers-iq/nexus-eval-harness/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 nexus-eval-harness

Your own site · 80×15
<a href="https://agentmods.dev/skills/cbruyndoncx/thirdbrain-mcpservers-iq/nexus-eval-harness"><img src="https://agentmods.dev/badge/skills/cbruyndoncx/thirdbrain-mcpservers-iq/nexus-eval-harness.svg" alt="Reviewed on agentmods" width="80" height="20"></a>
Per session 96 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 1,022 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 unknown 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 $0.00096 $0.01022
Opus 5 $0.00048 $0.00511
Sonnet 5 $0.00019 $0.00204
Haiku 4.5 $0.00010 $0.00102

Measured yesterday against content hash f9987c8f388f, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-15, from the pricing page.

Security

Grade A, and why

nexus-eval-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 yesterday.

The scan reads SKILL.md. This mod also ships 1 executable file (scripts/check_scenarios.py), listed below but not scanned — reading those needs a real analyzer, not pattern matching.

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.

nexus/.claude/skills/nexus-eval-harness/SKILL.md · 80 lines

The source is not reproduced here

No licence file

A repository with no LICENSE is all rights reserved by default, so the body is not copied here. The metadata, the measurements and the link are.

Read it on GitHub

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. yesterday First seen · 80 lines · 96 tokens per session scan A f9987c8f388f

Subscribe to this mod's changes

nexus-eval-harness is a skill published in the GitHub repository cbruyndoncx/ThirdBrAIn-MCPSERVERS-IQ (0 stars, last pushed 2d ago), with no licence file. It adds 96 tokens to every session and 1,022 once invoked, about $0.0005 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 2026-09-14.

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