An open-source (MIT) design rule set published by Together AI. It installs into AI coding tools such as Claude Code, Cursor, and Codex with a single npx command, and removes the “obviously made by AI” look from AI-generated web pages. Twenty themes steer typography, color, spacing, and motion, while a 57-item detection gate blocks classic “AI slop” patterns like purple-gradient hero sections and icon-tile cards. It offers four operations — build, study, audit, and redesign — and can diagnose weaknesses in existing pages or reproduce only the structure of a reference design.
Key Features
- 57-item slop detection gate: Checks output before delivery for patterns typical of AI-generated pages — purple-gradient heroes, Inter used for both display and body text, fully centered layouts, icon-tile feature cards — and rejects them
- 20 design themes: Choose from a set of themes covering typography pairings, OKLCH-based color palettes, modular spacing, and motion. Custom themes tailored to your brief are also supported
- Four operation modes: Switch between “build” (the default, generating pages), “study” (analyzing reference designs), “audit” (diagnosing existing code), and “redesign” (rebuilding from the structure up)
- Study mode extracts structure only: Pulls just the layout structure (the design’s DNA) from a reference URL or screenshot and reproduces it in a different aesthetic — useful for learning structure rather than copying looks
- Audit mode diagnoses existing pages: Scores your page against anti-patterns and points out what looks “AI-generated”, without making any edits
- One npx command to install: Run
npx skills add nutlope/hallmarkand it is placed automatically into the convention directories of Claude Code, Cursor, and Codex
Pricing
| Plan | Price | Highlights |
|---|---|---|
| Open source | Free | MIT license. Full feature access; forking, modification, and redistribution allowed |
Pricing is as of August 2026. Check the official site for the latest information.
Pros & Cons
✅ Pros
- Tackles the “everything looks the same” problem of AI coding tools just by installing a rule set
- Free and open source (MIT), with no extra API keys or external service subscriptions required
- Works across the major AI coding tools: Claude Code, Cursor, and Codex
- Useful not only for generation but also for auditing and redesigning existing pages
- The study mode lets you legitimately learn only the “structure” of a reference site and expand it into a different aesthetic
⚠️ Cons
- Not a standalone app — it presupposes an AI coding tool such as Claude Code
- Being a rule set, the final quality still depends on the capability of the AI model you pair it with
- The themes and detection gates assume Western web design; adjustments specific to Japanese typography must be handled yourself
- A young project released in April 2026, so best practices and case studies are still accumulating
Comparison with Similar Services
| Comparison | Hallmark | frontend-design (Anthropic) | v0 (Vercel) |
|---|---|---|---|
| Type | Design rule set (skill) | Official design skill | AI UI generation service |
| Runs on | Claude Code / Cursor / Codex | Claude Code and others | Web app (standalone) |
| Highlights | 57-item slop detection, 20 themes, audit/redesign | General frontend design guidance | Generates React/Next.js UIs from prompts |
| Pricing | Free (MIT) | Free | Free tier / paid plans |
Hallmark positions itself not as a “generation service” but as “design discipline” you plug into the AI coding tool you already use. Rather than competing with UI generation services, it complements them by raising the quality of their output.
Who Is It For
- People whose landing pages and prototypes built with Claude Code or Cursor all end up with the same “AI face”
- Solo developers and small teams without a designer who want to mechanically enforce a quality bar for generated UIs
- Web professionals who want an objective diagnosis of what makes an existing page look “AI-generated”
- Anyone who wants to borrow only the structure — not the vibe — of a reference site to build pages with their own aesthetic
Summary
Hallmark is an open-source design rule set from Together AI, specialized in removing the “AI-generated look” from the output of AI coding tools. Its distinguishing trait is turning the often subjective question of “good design” into a mechanical gate, through concrete mechanisms: 57 slop detection items and 20 themes. It installs with a single npx command and is free to try, so if you are unhappy with how your AI-generated UIs look, a good first step is running the audit mode against a page you already have.