version: "1.0.0" name: nexus-model-eval description: Grade how well a model drives the Nexus two-tool protocol (getTools/useTools) and decide whether a low score is the model's fault or the harness's. Use when asked to grade, benchmark, rank or compare models on Nexus tool use, when picking a default model, or when an eval report needs interpreting.

Nexus model eval

Context: the harness in tests/eval/ shows a model the same two tools the app does — getTools for discovery, useTools for execution — and grades the calls it makes, not the prose it writes. This skill owns the verdict: which models to run, and what a FAIL actually means. Running, configuring and extending the harness itself belongs to nexus-eval-harness. This file routes; detail loads when you take the path.

Workflow

1. Get current truth before running anything. A model cannot be graded on a

fixture no model can satisfy, and the fixture set moves: ``bash ls tests/eval/scenarios/ tests/eval/configs/ python3 .claude/skills/nexus-eval-harness/scripts/check_scenarios.py python3 .claude/skills/nexus-model-eval/scripts/check_advertised_tools.py ` A non-zero exit from the scenario checker means some scenario can never pass; resolve that first, and the fix belongs to nexus-eval-harness`, not to this run. The advertised-tools gap is not a defect — it is the list of correct model behaviors this harness punishes, and you will need it in step 3.

1. Run the grade: protocols/grade-models.md. Read it before you start; a

summarized procedure is one you will improvise, and every scenario in the matrix costs live, billed API calls.

1. You MUST attribute every failure before you report a number:

protocols/attribute-failures.md. The harness fails models for things the model did not do, so a raw pass rate with unread failures is not a grade. scripts/summarize_eval.py --labels refuses to sign off while any failure is unlabelled.

1. Report both numbers — raw pass rate and the attributed rate that charges only

model-failure verdicts — plus what the excluded failures actually were. One number alone is either unfair to the model or unfair to the reader.

1. At the end of a session that used this skill, run protocols/self-refine.md.

Map

• protocols/ the procedures: grade-models.md (target list → run → artifacts),

attribute-failures.md (FAIL → verdict → defensible grade), self-refine.md.

• references/ read on demand: what-is-graded.md (what makes a scenario pass,

what a "turn" counts, how retries and exclusions move the number), harness-artifacts.md (symptom → cause → proof for failures the model did not cause — read this before blaming any model).

• scripts/ run them, do not reimplement:
• scripts/check_advertised_tools.py — the commands the eval system prompt

tells the model to use that the executor cannot run, so obeying the prompt scores as a hallucination.

• scripts/preflight_models.py — do these slugs exist, before the run spends

money proving they do not.

• scripts/summarize_eval.py — report JSON → per-model rollup, bucketed

failures, and an attribution that is checked rather than asserted.

• refinement-log.md what past sessions changed here and why.

Siblings

The boundary with nexus-eval-harness: it owns the instrument, this skill owns the verdict. Anything that changes the harness or its inputs — env knobs, target syntax, live mode and the headless vault, config YAML, scenario authoring, harness code — is that skill's. Anything that changes what you conclude about a model is this one's. When a run reveals a fixture defect, hand it over rather than fixing it here.

Also: nexus-model-updates owns provider model definitions and whether a model ID works at all (grade nothing until it does); nexus-testing owns Jest lanes and what a mock can prove; nexus-agents owns the two-tool contract the harness is imitating; nexus-llm-adapters owns the adapter a stream error comes from.