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Head to head · Design canvas · October 2026 research run

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.

MeliusMelius AI, Inc. · HTTP API C54.1/100#621 of 841 pen.devHigh Agency, Inc. · MCP server D47.6/100#739 of 841

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

CategoryWeight this runMeliuspen.devEdge
Reliability16%206933Melius +36
Performance10%pendingpendingpendingnot scored in this run
Schema & documentation13%16.27061Melius +9
Agent ergonomics13%16.25166pen.dev +15
Security & auth14%17.54333Melius +10
Payments & pricing10%12.52038pen.dev +18
Task success10%pendingpendingpendingnot scored in this run
Maintenance & community7%8.86659Melius +7
Transparency & trust7%8.85553Melius +2
Negative events≤1500
Total54.1 · C47.6 · D

Facts side by side

FactMeliuspen.dev
KindHTTP APIMCP server
VendorMelius AI, Inc.High Agency, Inc.
Hosted endpointhttps://api.melius.com/api/v1no (local only)
TransportsHTTP, Streamable HTTPstdio
AuthOAuth or keyOAuth or key
PricingFreemiumFreemium
x402nono
LicenceProprietary service under Melius's terms of service. The mel CLI on npm is MIT, with no public source repository foundProprietary. The CLI package on npm carries a proprietary licence file, and the apps fall under the vendor's EULA
Tools exposed756
Read-only variant documentednono
llms.txtyesno
Last release2026-09-102026-10-08
Terms last updatedno date given2026-10-06
Privacy policy last updatedno date given2026-10-06
Customer content may train modelsnot found in the textnot found in the text
Terms restrict automated accessyesyes
Terms restrict benchmarkingyesyes
Terms or service can change without noticeyesnot found in the text
Arbitration or class-action waiveryesnot found in the text
Popularity9 npm/wk3.5k 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.

Other comparisons with Melius or pen.dev

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