# Melius vs pen.dev

> Melius scores 54.1 (C) on agent readiness against pen.dev's 47.6 (D), and leads in 5 of 7 scored categories. pen.dev leads on agent ergonomics and payments & pricing. Both do design canvas. Category scores, facts, verdicts and agent notes side by side.

- Canonical: https://www.anchorterminal.com/compare/melius-vs-pen-dev
- Markdown: https://www.anchorterminal.com/compare/melius-vs-pen-dev.md (~2,050 tokens)
- Slim: https://www.anchorterminal.com/compare/melius-vs-pen-dev.min.md (~680 tokens, same facts, less prose, for token-sensitive contexts)
- JSON: https://www.anchorterminal.com/compare/melius-vs-pen-dev.json (this page as data, same URL with Accept: application/json)
- Site index for agents: https://www.anchorterminal.com/llms.txt (full text: https://www.anchorterminal.com/llms-full.txt)
- API: https://www.anchorterminal.com/api/v1/index.json
- Updated: 2026-10-09

Melius scores 54.1 (C) on agent readiness against pen.dev's 47.6 (D), and leads in 5 of 7 scored categories. pen.dev leads on agent ergonomics and payments & pricing. Both do design canvas.

- Melius: grade C, 54.1/100, rank #621 of 842. Markdown https://www.anchorterminal.com/tools/melius.md · JSON https://www.anchorterminal.com/api/v1/tools/melius.json
- pen.dev: grade D, 47.6/100, rank #740 of 842. Markdown https://www.anchorterminal.com/tools/pen-dev.md · JSON https://www.anchorterminal.com/api/v1/tools/pen-dev.json

## Which one, for what

### Melius (C)

Good for: An agent producing batches of ad creative, product images or short videos on a shared canvas that people then review, with many models behind one key.

Ahead on:
- Reliability, 69 against 33
- Schema & documentation, 70 against 61
- Security & auth, 43 against 33
- Maintenance & community, 66 against 59

Also in its favour:
- A hosted endpoint, with nothing to install

Watch for: API keys have no scopes. A key works with its creator's role in every team the creator belongs to

### pen.dev (D)

Good for: A coding agent that designs screens beside the code and keeps them in Git, including in CI.

Ahead on:
- Agent ergonomics, 66 against 51
- Payments & pricing, 38 against 20

Also in its favour:
- Runs on your own machine

Watch for: No changelog. The three desktop releases on GitHub have empty notes, and the format docs reserve the right to make breaking changes


## Score by category

| Category | Weight | Melius | pen.dev | Edge |
| --- | --- | --- | --- | --- |
| Reliability | 16% (20 this run) | 69 | 33 | Melius +36 |
| Performance | 10%, pending | pending | pending | not scored in this run |
| Schema & documentation | 13% (16.2 this run) | 70 | 61 | Melius +9 |
| Agent ergonomics | 13% (16.2 this run) | 51 | 66 | pen.dev +15 |
| Security & auth | 14% (17.5 this run) | 43 | 33 | Melius +10 |
| Payments & pricing | 10% (12.5 this run) | 20 | 38 | pen.dev +18 |
| Task success | 10%, pending | pending | pending | not scored in this run |
| Maintenance & community | 7% (8.8 this run) | 66 | 59 | Melius +7 |
| Transparency & trust | 7% (8.8 this run) | 55 | 53 | Melius +2 |
| Negative events | ≤15 | 0 | 0 | |
| **Total** | | **54.1 · C** | **47.6 · D** | |

## Facts side by side

| Fact | Melius | pen.dev |
| --- | --- | --- |
| Kind | HTTP API | MCP server |
| Vendor | Melius AI, Inc. | High Agency, Inc. |
| Hosted endpoint | `https://api.melius.com/api/v1` | no (local only) |
| Transports | HTTP, Streamable HTTP | stdio |
| Auth | OAuth or key | OAuth or key |
| Pricing | Freemium | Freemium |
| x402 | no | no |
| Licence | Proprietary service under Melius's terms of service. The mel CLI on npm is MIT, with no public source repository found | Proprietary. The CLI package on npm carries a proprietary licence file, and the apps fall under the vendor's EULA |
| Tools exposed | 75 | 6 |
| Read-only variant documented | no | no |
| llms.txt | yes | no |
| Last release | 2026-09-10 | 2026-10-08 |
| Terms last updated | no date given | 2026-10-06 |
| Privacy policy last updated | no date given | 2026-10-06 |
| Customer content may train models | not found in the text | not found in the text |
| Terms restrict automated access | yes | yes |
| Terms restrict benchmarking | yes | yes |
| Terms or service can change without notice | yes | not found in the text |
| Arbitration or class-action waiver | yes | not found in the text |
| Popularity | 9 npm/wk | 3.5k npm/wk |

## Verdicts

**Melius.** One backend serves a 59-operation REST API with a public OpenAPI spec, a hosted MCP server with OAuth sign-in and a JSON-only CLI, and the status page shows no incidents since July 2026. API keys carry no scopes and work with their creator's role, and no rate-limit numbers, changelog or per-model credit prices are published.

**pen.dev.** An agent can create, edit and export `.pen` designs without a GUI through the `pen` CLI, with four compact MCP tools that carry annotations and a documented JSON format. The software is closed and needs a pen.dev account. No changelog, status page or security contact was found, and 14 public issue reports had no reply on 8 October 2026.

## Before you call either

### Melius

1. Generate by creating a node on a canvas, starting a run with POST /nodes/{nodeId}/runs, then polling GET /node-runs/{nodeRunId} until `status` is finished or failed
2. Over MCP, call `get_guide` first, `show_presence` before node changes and `canvas_plan_layout` before `bulk_create_nodes`
3. On 429 wait `Retry-After` seconds. After a timeout or 5xx on a write, read the canvas or run state before resubmitting, because there are no idempotency keys
4. Read credit costs from GET /generation/models?category=image before a bulk run. A 400 can mean the team is out of credits
5. Downloads arrive as a ZIP from a signed URL. Fetch that URL without the `Authorization` header

### pen.dev

1. Call `read_skill()`, then `read_skill({ path: "pen-schema.md" })` and `read_skill({ path: "execute.md" })` before the first `execute`. The tool description alone doesn't document the operations
2. Call `get_app_state()` and confirm the active document before editing. The MCP server works on whichever `.pen` file is open in the app
3. In headless `pen interactive`, call `save()` before `exit()`, and keep `--in` and `--out` on different paths to preserve the source
4. Check that an export file exists. The docs say an export failure can print an error without a nonzero exit status
5. In CI set `PEN_CLI_KEY` plus a provider key such as `ANTHROPIC_API_KEY`. Run `pen version`, since `pen --version` is not a flag

## Questions

### Which is better for AI agents, Melius or pen.dev?

Melius scores 54.1 (C) on agent readiness against pen.dev's 47.6 (D), and leads in 5 of 7 scored categories. pen.dev leads on agent ergonomics and payments & pricing.

### Do Melius and pen.dev need an API key?

Both take an API key or an OAuth sign-in.

### Can an agent call Melius and pen.dev without installing anything?

Melius has a hosted endpoint at https://api.melius.com/api/v1. pen.dev runs on your own machine, with no hosted endpoint listed.


## For agents

- This comparison as JSON: https://www.anchorterminal.com/compare/melius-vs-pen-dev.json, and with the fewest tokens: https://www.anchorterminal.com/compare/melius-vs-pen-dev.min.md
- Over MCP at https://www.anchorterminal.com/mcp (no key): `compare_tools {"a": "melius", "b": "pen-dev"}`. From a terminal: `anchor compare melius pen-dev`
- Each listing in full: https://www.anchorterminal.com/api/v1/tools/melius.json and https://www.anchorterminal.com/api/v1/tools/pen-dev.json

## Other comparisons with Melius or pen.dev

- [Figma API + MCP vs Melius](https://www.anchorterminal.com/compare/figma-mcp-vs-melius.md)
- [Figma API + MCP vs pen.dev](https://www.anchorterminal.com/compare/figma-mcp-vs-pen-dev.md)
- [Framer Server API vs Melius](https://www.anchorterminal.com/compare/framer-vs-melius.md)
- [Framer Server API vs pen.dev](https://www.anchorterminal.com/compare/framer-vs-pen-dev.md)
- [Miro API + MCP vs pen.dev](https://www.anchorterminal.com/compare/miro-vs-pen-dev.md)
- [pen.dev vs Penpot API + MCP](https://www.anchorterminal.com/compare/pen-dev-vs-penpot.md)
- [Melius vs Miro API + MCP](https://www.anchorterminal.com/compare/melius-vs-miro.md)
- [Melius vs Penpot API + MCP](https://www.anchorterminal.com/compare/melius-vs-penpot.md)