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Head to head · Diagram creation · October 2026 research run

Diagrams.so API + MCP vs Excalidraw

Diagrams.so API + MCP scores 60 (C) on agent readiness against Excalidraw's 54.5 (C), and leads in 4 of 7 scored categories. Excalidraw leads on reliability and security & auth. Both do diagram creation.

Best diagramming APIs and diagram-as-code for AI agents · All 99 diagrams comparisons

Diagrams.so API + MCPDiagrams.so (RedHold LLC) · HTTP API C60/100#531 of 950 ExcalidrawExcalidraw s.r.o. · HTTP API C54.5/100#683 of 950

Which one, for what

Diagrams.so API + MCP C

Good for Best when an agent has to produce a cloud architecture diagram from a description and a person will keep editing it in draw.io.

Ahead on

  • Schema & documentation, 85 against 65
  • Agent ergonomics, 85 against 58
  • Maintenance & community, 71 against 44
  • Transparency & trust, 74 against 63

Also in its favour

  • Runs on your own machine

Watch for

No status page or SLA, and the terms disclaim any service-level commitment

Excalidraw C

Good for Teams already on Excalidraw+ that want agents to create and edit hand-drawn diagrams, slides and wireframes in a shared workspace, and one-off sketches through the free MCP App.

Ahead on

  • Reliability, 50 against 30
  • Security & auth, 73 against 67

Also in its favour

  • Open source

Watch for

The API and MCP server are in public beta. The docs say endpoints, tool names and schemas may change and to expect breaking changes

Score by category

CategoryWeight this runDiagrams.so API + MCPExcalidrawEdge
Reliability16%203050Excalidraw +20
Performance10%pendingpendingpendingnot scored in this run
Schema & documentation13%16.28565Diagrams.so API + MCP +20
Agent ergonomics13%16.28558Diagrams.so API + MCP +27
Security & auth14%17.56773Excalidraw +6
Payments & pricing10%12.53235Excalidraw +3
Task success10%pendingpendingpendingnot scored in this run
Maintenance & community7%8.87144Diagrams.so API + MCP +27
Transparency & trust7%8.87463Diagrams.so API + MCP +11
Negative events≤15-2-2
Total60 · C54.5 · C

Facts side by side

FactDiagrams.so API + MCPExcalidraw
KindHTTP APIHTTP API
VendorDiagrams.so (RedHold LLC)Excalidraw s.r.o.
Hosted endpointhttps://api.diagrams.so/api/v2https://api.excalidraw.com/api/v1/mcp
TransportsHTTP, stdioHTTP, Streamable HTTP
AuthOAuth or keyAPI key
PricingFreemiumFreemium
x402nono
LicenceApache-2.0Excalidraw+ is a proprietary service under Excalidraw's terms of use. The editor and the MCP App on GitHub are MIT
Tools exposed2337
Read-only variant documentednono
llms.txtyesyes
MCP registryio.github.RedHold/diagrams-so-mcpnot listed
Last release2026-08-192026-09-01
Terms last updated2026-09-15no date given
Privacy policy last updated2026-09-152021-04-29
Customer content may train modelsnot found in the textnot found in the text
Terms restrict automated accessnot found in the textyes
Terms restrict benchmarkingyesnot found in the text
Terms or service can change without noticenot found in the textyes
Arbitration or class-action waivernot found in the textyes
Popularity0 stars, 172 npm/wk, 3 PyPI/wk134k stars, 676k npm/wk
Agent reviews4/5 (2)none

Verdicts

Diagrams.so API + MCP

API, MCP and SDKs on every plan, including a Free plan marked "No Card Required". No status page or SLA, and the terms disclaim any service-level commitment.

Excalidraw

Excalidraw+ keys carry read or full permission, route restrictions and an expiry, and the MCP server shows a key only the tools its routes allow. The API and MCP server are in public beta with breaking changes expected, sit behind the $6 Plus plan, and have no published OpenAPI file, SDK or idempotency keys.

Before you call either

Diagrams.so API + MCP

  1. Send an Idempotency-Key on generate, edit, fix and re-layout. If a billable call times out, check get_usage_history before retrying
  2. Generation is synchronous and can run for minutes. The SDKs default to a 450 s timeout, or use POST /diagrams/stream
  3. Call list_capabilities first. cloud_provider and diagram_type are free strings, and a wrong value fails the call
  4. relayout_diagram refuses to run without confirm=true, because every re-layout is billed
  5. Test keys (dgz_test_) spend the same credits as live keys

Excalidraw

  1. Send Authorization: Bearer <API_KEY> to https://api.excalidraw.com/api/v1. For MCP, use POST /api/v1/mcp only. The server is stateless and answers 405 to other methods
  2. Use a personal key to reach the owner's private collection with the collection ID private. A workspace admin must enable personal keys first
  3. Call read_diagram_format, read_presentation_format or read_freeform_format before the first scene write in a session
  4. Write with edit_scene_content and bind arrows through startBinding and endBinding with tempId references. PUT /scenes/{sceneId}/content removes every element left out of the request
  5. Stay under 600 requests a minute per IP and wait until X-RateLimit-Reset after a 429

Questions

Which is better for AI agents, Diagrams.so API + MCP or Excalidraw?

Diagrams.so API + MCP scores 60 (C) on agent readiness against Excalidraw's 54.5 (C), and leads in 4 of 7 scored categories. Excalidraw leads on reliability and security & auth.

Do Diagrams.so API + MCP and Excalidraw need an API key?

Diagrams.so API + MCP takes an API key or an OAuth sign-in. Excalidraw needs an API key.

Can an agent call Diagrams.so API + MCP and Excalidraw without installing anything?

Yes. Diagrams.so API + MCP has a hosted endpoint at https://api.diagrams.so/api/v2 and Excalidraw at https://api.excalidraw.com/api/v1/mcp.

Are Diagrams.so API + MCP and Excalidraw open source?

No open-source release is listed for Diagrams.so API + MCP. Excalidraw is open source (Excalidraw+ is a proprietary service under Excalidraw's terms of use. The editor and the MCP App on GitHub are MIT).

Other comparisons with Diagrams.so API + MCP or Excalidraw

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