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 plugin-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/plugin-builder)<a href="https://agentmods.dev/skills/vellum-ai/vellum-assistant/plugin-builder"><img src="https://agentmods.dev/badge/skills/vellum-ai/vellum-assistant/plugin-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/plugin-builder"><img src="https://agentmods.dev/badge/skills/vellum-ai/vellum-assistant/plugin-builder.svg" alt="Reviewed on agentmods" width="80" height="20"></a>- NVIDIA SkillSpector warn
SkillSpector: 1 finding, up to medium
These are SkillSpector’s own severities. On a checked sample its high-severity flags on skills were ~96% false positives — a documented command, a public API, a “never do X” rule — so we show them as a caution to read, not a verdict. Why →
- medium Prompt Injection · line 45 Large whitespace padding was detected (a block of blank lines or a long run of spaces). This can push injected instructions below or to the right of the visible area so a human reviewer never sees them while the agent still reads them. Manual review of the hidden content is recommended.Fix: Remove the large whitespace padding (blank-line blocks or long space runs) and review any content hidden below or to the right of it. Keep skill files compact and reviewable so no instructions can be
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 | $0.00042 | $0.02547 |
| Opus 5 | $0.00021 | $0.01273 |
| Sonnet 5 | $0.00008 | $0.00509 |
| Haiku 4.5 | $0.00004 | $0.00255 |
Grade A, and why
plugin-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 today.
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 — 131 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Plugin Builder
Build on top of Vellum with plugins. A plugin bundles multiple surfaces into a single installable package that extends what an assistant can do.
Plugins are in beta. The peer-dep range you declare is what gets you load. Treat everything you write as something that can break between Vellum releases until 1.0 ships, and pin a real range.
What is a plugin?
A plugin is a directory in the assistant's workspace (<workspaceDir>/plugins/<name>/) that groups different surfaces into one cohesive capability. The assistant can build plugins directly in this folder or install one from the community via the CLI:
assistant plugins install <name>
Plugins can also be discovered and managed from the Plugins tab in the app, or searched from the CLI with assistant plugins search. The catalog is a curated allowlist that the Vellum team approves and curates.
The surfaces a plugin can bundle
A single plugin can contribute several different kinds of behavior. Each surface is discovered by convention from a named subdirectory. Missing directories are simply skipped, so a plugin contributes only what it ships.
| Surface | Lives in | What it does |
|---|---|---|
| Lifecycle hooks | hooks/<name>.ts |
Run code at fixed points in the Assistant's lifecycle to read or transform what flows through, and broadcast progress to the UI. |
| Skills | skills/<name>/ |
Directories of instructions and associated assets, scripts, and resources that the Assistant loads dynamically when relevant. |
| Model-visible tools | tools/<name>.ts |
Add new tools the model can call. Plugin tools land in the same catalog as built-in tools. |
| MCP servers | mcp.json |
Declare MCP servers the assistant connects on install. Their tools land as mcp__<id>__<tool> alongside workspace-configured MCP tools. |
| HTTP routes | routes/<path>.ts |
Serve HTTP endpoints in the plugin's own /x/plugins/<name>/ namespace (apps, local callers, and the handler behind public ingress). |
| Channels | channels/ingress.json |
Declare public webhook and WebSocket routes that make the plugin a channel. The gateway verifies them and forwards to matching routes. |
| Apps | apps/<name>/ |
Ship persistent interactive apps (dashboards, trackers, visualizations) compiled from a Preact + TSX bundle and rendered in the workspace panel. |
What ships with it
9 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.
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.
- today Changed e9f6d60c04d0
- 9d ago Changed · -4 lines 8e06fcc41a4f
- 9d ago First seen · 135 lines · 42 tokens per session scan A 5d244e4190f6
plugin-builder is a skill published in the GitHub repository vellum-ai/vellum-assistant (1,234 stars, last pushed today), licensed MIT. It adds 42 tokens to every session and 2,547 once invoked, about $0.0002 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 2026-09-03.
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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 …
continual-learning
Nightly refinement of an existing per-repo review-style prompt using this reviewer's own finding outcomes. Read confirmed (resolved-by-commit / thumbs-up) and dismissed (thumbs-down) findings, promote the bug patterns the team actually fixes, demote the false-positive patterns, reconcile against the current prompt…
ha-logs
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