What is nexus-eval-harness?

A test harness for evaluating language-model agents through scenarios, tool calls, assertions, executors, and reports. An evaluation checks whether an agent behaves as expected on a defined task.

Adding or repairing evaluation scenarios, configuring runs, changing test components, and investigating reports.

It helps explain empty runs, all-failing runs, inconsistent scores, and incorrect test fixtures instead of treating every result as a model problem.

How ProfSynapse/nexus configures Claude Code and Codex

Reuse

Borrowing it

Nothing to install: this file belongs to ProfSynapse/nexus. Take a copy, put it at the same path in your own repository, and replace the rules that are about this project with yours.

Copy the file

curl -O https://raw.githubusercontent.com/ProfSynapse/nexus/main/.claude/skills/nexus-eval-harness/SKILL.md

Clone the repo

git clone --depth 1 https://github.com/ProfSynapse/nexus

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.

README.md

[![agentmods](https://agentmods.dev/badge/skills/profsynapse/nexus/nexus-eval-harness/github.svg)](https://agentmods.dev/skills/profsynapse/nexus/nexus-eval-harness)

Your own site

<a href="https://agentmods.dev/skills/profsynapse/nexus/nexus-eval-harness"><img src="https://agentmods.dev/badge/skills/profsynapse/nexus/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.

Your own site · 80×15

<a href="https://agentmods.dev/skills/profsynapse/nexus/nexus-eval-harness"><img src="https://agentmods.dev/badge/skills/profsynapse/nexus/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. Third-party audits

NVIDIA SkillSpector pass 7 Sept 2026

How audits are shown

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.

Model	Per session	Once invoked
Fable 5.1	$0.00096	$0.01022
Opus 5.5	$0.00038	$0.00409
Sonnet 5.5	$0.00019	$0.00204
Haiku 4.5	$0.00010	$0.00102

Measured 2mo ago against content hash f9987c8f388f, method: parsed. Prices are Anthropic first-party input rates as of 2026-10-07, 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 2mo ago.

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.

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

How it starts

The opening of the file, as written. The whole thing — 80 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Nexus Eval Harness

Context: the harness under tests/eval/ drives the real production path — StreamingOrchestrator plus tool continuation — with a mock or live tool executor swapped in, and grades the tool calls a model emits. It is a fixture system, and almost every surprising result is the fixture talking, not the model. This skill owns the fixtures, the configs, the executors and the reports.

Workflow

Pick the job and open its protocol. Work from the protocol; this router names procedures, it does not contain them.

Job	Protocol
Add a scenario, or fix one that grades wrongly	`protocols/add-a-scenario.md`
Write or change a config, choose targets, mode, retries	`protocols/configure-a-run.md`
A run produced nothing, all-fails, a hang, or odd numbers	`protocols/debug-a-run.md`
Change the executors, assertions, loader or reports	`protocols/extend-the-harness.md`

Derive every list from the tree, never from this skill. It names no scenarios, no configs, no models and no env-var table on purpose, and you MUST NOT add one — the harness gains knobs faster than a document survives.

ls tests/eval/scenarios/ tests/eval/configs/
grep -rhoE "get(Number|List)?Env\('[A-Z_]+'\)|process\.env\.[A-Z_]+" tests/eval/ \
  | grep -oE "[A-Z][A-Z_]{3,}" | sort -u    # every knob, including the
                                            # ones ConfigLoader mediates

Before calling any scenario change done, run the checker from the repo root and fix everything it prints:
```
python3 .claude/skills/nexus-eval-harness/scripts/check_scenarios.py
```
NEVER trust jest's exit code as the verdict on a run, and never report a pass rate you read from stdout. The saved reports under the configured artifacts dir are the only source of truth, and they are written even when the run times out — see references/run-behavior.md.
At the end of a session that used this skill, run protocols/self-refine.md.

Read the full file on GitHub · 80 lines

Files

What ships with it

11 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.

2mo ago 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 ProfSynapse/nexus (158 stars, last pushed 5d ago), licensed MIT. It adds 96 tokens to every session and 1,022 once invoked, about $0.0004 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 2026-08-30.

Testing

research-engineer

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davidondrej/skills · 68 tokens

nexus: Skill for Claude Code