Vellum Assistant is a personal AI assistant that remembers information about users, learns their preferences, and takes actions across connected apps. It is intended for people who want an assistant that can manage conversations, unfinished work, and proactive notifications over time. The catalogue skills, hooks, instruction, and setting configure or extend how the assistant works.
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.
npx skills add vellum-ai/vellum-assistant --skill app-buildergit clone --depth 1 https://github.com/vellum-ai/vellum-assistantWrote 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.
[](https://agentmods.dev/skills/vellum-ai/vellum-assistant/app-builder)<a href="https://agentmods.dev/skills/vellum-ai/vellum-assistant/app-builder"><img src="https://agentmods.dev/badge/skills/vellum-ai/vellum-assistant/app-builder/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.
<a href="https://agentmods.dev/skills/vellum-ai/vellum-assistant/app-builder"><img src="https://agentmods.dev/badge/skills/vellum-ai/vellum-assistant/app-builder.svg" alt="Reviewed on agentmods" width="80" height="20"></a>- NVIDIA SkillSpector pass
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 | $0.00162 | $0.07225 |
| Opus 5.5 | $0.00065 | $0.02890 |
| Sonnet 5.5 | $0.00032 | $0.01445 |
| Haiku 4.5 | $0.00016 | $0.00722 |
Grade A, and why
app-builder 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 1mo 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.
How it starts
The opening of the file, as written. The whole thing — 372 lines — stays where its author put it; the contents beside it link to each section on GitHub.
You build small, personal visual tools — dashboards, trackers, calculators, data visualizations, simple landing pages, and slide decks. These are quick, single-user tools the user wants for themselves, not products they ship to other people.
Move fast: think, plan in one pass, pick a striking visual direction following the frontend-design skill (included with this load — see Included Skill: Frontend Design below), and build it immediately. Don't ask permission to be creative — pick the colors, the layout, the atmosphere, the micro-interactions. Every tool gets its own identity: a plant tracker feels earthy and green, a finance dashboard precise and navy. They should feel designed, not generated.
Design quality is delegated to the frontend-design skill, and you MUST follow it completely. That skill owns the aesthetics (typography, color, motion); this skill owns the technical infrastructure (sandbox, data, widgets, lifecycle). Its instructions load automatically with this skill — if they are missing (listed under Suggested Included Skills (not loaded)), call skill_load("frontend-design") before building anything. Building without them gives generic, templated UI, which is a failed build.
Scope — what belongs here, what doesn't
Build here (the default — lean toward it): a tool the user wants for themselves. A dashboard, tracker, calculator, data viz, slide deck, or a simple landing page they'll use on their own. Personal and self-contained.
Does NOT belong here: anything complex, multi-user, or meant to be published, deployed, handed off, or shipped to other people. Sandbox apps are single-user, run only in this preview, and can't be exported or deployed. They're the wrong home for a real product.
When a request is for a shippable/complex app, don't build in the sandbox. Instead:
- Explain the approach in a sentence: a real product belongs in a project folder they own — version-controlled, deployable, shareable — and you'll build it with them as a coding agent, not inside a preview.
- Establish a project folder (propose a path, or use one they name).
- Hand off to a coding agent:
skill_load("acp")→acp_spawn({ task: "<what to build>", cwd: "<folder>" })(agent defaults toclaude), then follow theacpskill.
Triage on intent, not artifact type. A simple landing page is a personal build by default — it only becomes a handoff when the user signals they want to publish or share it. When the signal is weak, lean personal and just build. If you genuinely can't tell, ask exactly one short question.
Editing an existing sandbox app? Skip scope entirely — that's iteration. Resolve the app (see below), open it, and go to Iteration.
What ships with it
19 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.
- icon.svg 487 B
- references/CUSTOM_ROUTES.md 7.3 KB
- references/DESIGN_SYSTEM.md 3.6 KB
- references/examples/expense-tracker.md 12 KB
- references/examples/focus-timer.md 8.3 KB
- references/examples/habit-tracker.md 12 KB
- references/examples/README.md 1.2 KB
- references/INTERACTION_HOOKS.md 3.5 KB
- references/RESPONSIVE.md 3.0 KB
- references/SLIDES.md 1.9 KB
- references/WIDGETS.md 5.1 KB
- TOOLS.json 9.5 KB
- tools/app-create.ts 712 B runs code
- tools/app-delete.ts 514 B runs code
- tools/app-generate-icon.ts 878 B runs code
- tools/app-list.ts 1.6 KB runs code
- tools/app-open.ts 1.1 KB runs code
- tools/app-refresh.ts 709 B runs code
- tools/app-update.ts 834 B runs code
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.
- 1mo ago Changed · +5 lines 9fff654b8f61
- 1mo ago First seen · 367 lines · 162 tokens per session scan A 09c28514c018
app-builder is a skill published in the GitHub repository vellum-ai/vellum-assistant (1,450 stars, last pushed 2d ago), licensed MIT. It adds 162 tokens to every session and 7,225 once invoked, about $0.0006 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.
Other skills, from other repositories
lictor-security-check
Pre-release security audit for ANY project — AI-built or hand-written, web or mobile. Scans the codebase for the full range of real-world risks that get apps breached: leaked API & AI-provider keys, exposed configs/secrets, broken auth & access control (IDOR), injection (SQL/XSS/command), SSRF, open databases & cloud…
lictor-rotate
Walks the user through rotating a leaked API key — step by step, provider-specific. Knows the exact URL to visit, the exact button to click, and how to verify the rotation worked. Supports Stripe, OpenAI, Anthropic, Google Cloud / AI Studio, GitHub, AWS, Slack, Supabase, Firebase, Postmark, and generic OAuth providers.
lictor-explain
Takes any security finding, error message, or jargon-heavy security advice and explains it in plain English. Use this when someone is confused by what /lictor-security-check found, or when they got a security warning from another tool and don't understand it.
lictor-fix-it
Applies the fixes recommended by /lictor-security-check, with the user's explicit permission for each change. Walks through findings one at a time, shows the proposed change, gets approval, applies, runs tests if available, and moves on. Some fixes (rotating leaked credentials) require the user to act outside Claude …
ha-logs
A read-only troubleshooting skill for querying Hope Agent’s local SQLite databases, which store logs, conversations, and background-job status.
getting-started
Interactive post-onboarding tour that adapts to whatever data exists (calendar, Granola, or none). Use right after onboarding, or when the user says 'show me around', 'how do I start'. Also use proactively when the vault is < 7 days old. Not for the initial setup itself; use setup.