boxel: Skill for Claude Code

.claude/skills/ai-assistant-evals/SKILL.md

ai-assistant-evals is a skill for Claude Code from cardstack/boxel. It costs 224 tokens per session (5,818 once invoked), scanned A, original, MIT.

A test suite that drives the real local AI assistant in a browser and checks what each language model builds in a fresh workspace. It records results for a fixed prompt or an evaluation card, which is a task with grading criteria.

In plain words
What is it for?
Use it to run model evaluations, inspect whether the assistant created the expected result, and review the recorded events and per-model outcomes.
Why use it?
It tests the complete assistant experience rather than only isolated code, while making the model results comparable. Runs use the real provider, cost money, and leave test data behind.

Skill for Claude Code

Written for Claude Code: installed under .claude/. Also seen: reads .claude/ paths; positional $N argument.

This is cardstack/boxel's own configuration. It tells Claude Code how to work on boxel itself, so it is not a mod to install elsewhere. Copy it as a starting point and replace the rules that are about this project. Everything boxel configures →

Needs its repository: it runs a file that does not travel with it, so clone the repository first. The line is node .claude/skills/inspect-ai-room/scripts/inspect-room.mjs usage '<roomId>'.

Reuse

Borrowing it

Nothing to install: this file belongs to cardstack/boxel. 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/cardstack/boxel/main/.claude/skills/ai-assistant-evals/SKILL.md
Clone the repo
git clone --depth 1 https://github.com/cardstack/boxel

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.

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README.md
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Per session 224 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 5,818 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 1 finding. A grade says what 26 rules found in the file — not that it is safe.
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 $0.00224 $0.05818
Opus 5.5 $0.00090 $0.02327
Sonnet 5.5 $0.00045 $0.01164
Haiku 4.5 $0.00022 $0.00582

Measured yesterday against content hash 8e7ccaf18c32, method: parsed. Prices are Anthropic first-party input rates as of 2026-10-07, from the pricing page.

Security

Grade A, and why

ai-assistant-evals scanned grade A with 1 finding 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.

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.

Makes network callslowCapability

Not a fault in itself. Listed so you know the mod talks to something, and to what.

ai-bot. Check: `curl -sk -o /dev/null -w '%{http_code}' https://localhost:4200/`
.claude/skills/ai-assistant-evals/SKILL.md · 343 lines

How it starts

The opening of the file, as written. The whole thing — 343 lines — stays where its author put it; the contents beside it link to each section on GitHub.

AI assistant evals

packages/ai-assistant-evals holds a Playwright spec that does, per model, what a person did by hand all week: log in, create a workspace, open a room, pick the model, send "create a hello world card and show it", wait until the bot is idle, check a card rendered, and read the room's events for the numbers. One row per model.

It runs against the REAL local stack and the REAL provider. Every run spends money (a few cents for a good model, up to a few dollars for a bad one) and leaves a workspace and a room behind on the local synapse and realm server. Do not run it to "see what happens", do not loop it, and do not rerun a model whose result you have not read yet.

Bare prompt or evaluation

pnpm eval:models is the fixed hello-world prompt, graded mechanically, nothing written anywhere but eval-results/. pnpm eval <evaluation-card-url> is the same browser flow fed by an EvaluationCard: the card's prompt and follow-up prompts, its initial cards and files copied into the test workspace first, a per-session results directory, and one EvaluationResultCard per model plus one EvaluationReportCard written into the workspace the evaluation lives in (the writer's AI Assistant Evaluations workspace, at the endpoint evals, made by pnpm eval:setup). The quality score on a result is a judge's, not the runner's: the /run-ai-assistant-eval command in .claude/commands walks through running, judging against the card's success criteria, and recording the score with pnpm eval:judge. Everything below about watching a run, grades, verdicts and benchmarks applies to both. For an evaluation with follow-up prompts the turn and time targets are multiplied by the number of prompts.

A change to the boxel-skills content that targets one of the assistant's core use cases needs an evaluation that shows the problem and the with/without numbers: the skill-change-eval skill covers writing it and what counts as evidence.

Prerequisites

  • The dev stack is up: mise run dev-all with OPENROUTER_API_KEY set for the ai-bot. Check: curl -sk -o /dev/null -w '%{http_code}' https://localhost:4200/ prints 200.
  • Every eval user holds at least 3000 credits. Running out mid-session turns the assistant's reply into "There was an error processing your request" and wastes the run, so top up first — the balance is the sum of that user's credits_ledger rows and a top-up is one extra_credit row. The /run-ai-assistant-eval command's preflight carries the query.
  • The local matrix users ai-assistant-eval-user-1 to ai-assistant-eval-user-5 / password exist (see EVAL_USERS below). pnpm eval:users registers whoever is missing, and pnpm eval refuses to start without them rather than failing on the first browser action of a paid run. For evaluations, pnpm eval:setup has created the AI Assistant Evaluations workspace of the writer user (user locally), at the endpoint evals, and pushed the cards.
  • Every model you name has a ModelConfiguration card in the SystemCard the host uses (packages/catalog/contents/SystemCard/default.json), or the picker will not offer it.
  • Playwright's Chromium is installed (pnpm exec playwright install chromium in packages/ai-assistant-evals if a run complains).

Read the full file on GitHub · 343 lines

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 Changed · +5 lines 8e7ccaf18c32
  2. 3d ago Changed · +5 lines eec34b65d8b8
  3. 5d ago First seen · 333 lines · 224 tokens per session scan A 6c3dcdba50f3

Subscribe to this mod's changes

ai-assistant-evals is a skill published in the GitHub repository cardstack/boxel (27 stars, last pushed today), licensed MIT. It adds 224 tokens to every session and 5,818 once invoked, about $0.0009 per session on Opus 5.5. A static security scan graded it A with 1 finding (makes network calls). No closer match exists in the catalogue, so it is treated as the original; first seen 2026-10-21.

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