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Head to head · Diagram create · October 2026 research run

Diagrams.so API + MCP vs PlantUML

PlantUML scores 66.9 (B) on agent readiness against Diagrams.so API + MCP's 60 (C), and leads in 3 of 7 scored categories. Diagrams.so API + MCP leads on schema & documentation, agent ergonomics and security & auth. Both do diagram create.

Diagrams.so API + MCPDiagrams.so (RedHold LLC) · HTTP API C60/100#481 of 841 PlantUMLPlantUML project (Arnaud Roques) · SDK + MCP B66.9/100#251 of 841

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 78
  • Security & auth, 67 against 50

Also in its favour

  • A hosted endpoint, with nothing to install
  • Runs on your own machine

Watch for

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

PlantUML B

Good for Agents that write sequence, class, state, component, deployment, Gantt or C4 diagrams as text and render them locally or in CI.

Ahead on

  • Reliability, 83 against 30
  • Payments & pricing, 60 against 32

Also in its favour

  • No key needed to call it
  • Open source

Watch for

The default security profile is LEGACY, which gives diagram text full access to local files and URLs through !include. The docs say it will be removed, with no date

Score by category

CategoryWeight this runDiagrams.so API + MCPPlantUMLEdge
Reliability16%203083PlantUML +53
Performance10%pendingpendingpendingnot scored in this run
Schema & documentation13%16.28565Diagrams.so API + MCP +20
Agent ergonomics13%16.28578Diagrams.so API + MCP +7
Security & auth14%17.56750Diagrams.so API + MCP +17
Payments & pricing10%12.53260PlantUML +28
Task success10%pendingpendingpendingnot scored in this run
Maintenance & community7%8.87173PlantUML +2
Transparency & trust7%8.87473Diagrams.so API + MCP +1
Negative events≤15-2-2
Total60 · C66.9 · B

Facts side by side

FactDiagrams.so API + MCPPlantUML
KindHTTP APISDK + MCP
VendorDiagrams.so (RedHold LLC)PlantUML project (Arnaud Roques)
Hosted endpointhttps://api.diagrams.so/api/v2no (local only)
TransportsHTTP, stdio
AuthOAuth or keyNone
PricingFreemiumFree
x402nono
LicenceApache-2.0GPL-3.0-or-later
Tools exposed23none
Read-only variant documentednono
llms.txtyesno
MCP registryio.github.RedHold/diagrams-so-mcpnot listed
Last release2026-08-192026-09-05
Terms last updated2026-09-15no document linked
Privacy policy last updated2026-09-15no document linked
Customer content may train modelsnot found in the text
Terms restrict automated accessnot found in the text
Terms restrict benchmarkingyes
Terms or service can change without noticenot found in the text
Arbitration or class-action waivernot found in the text
Popularity0 stars, 172 npm/wk, 3 PyPI/wk13k stars, 207 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.

PlantUML

One Java command reads diagram text from stdin and writes PNG, SVG, PDF or ASCII with no account, and CI passed on the last eight pushes. The default security profile lets diagram text read any local file and fetch any URL, and the documentation still lists chronology diagrams that release 1.2026.2 switched off.

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

PlantUML

  1. Set PLANTUML_SECURITY_PROFILE to SANDBOX or ALLOWLIST before rendering text from an untrusted source. The default profile lets !include read local files and fetch URLs
  2. Run java -jar plantuml.jar --check-syntax with -stdrpt first and read the exit status. Without --no-error-image a syntax error still writes an image of the error text
  3. Pass -pipe with --svg, --txt or --utxt to work without files. --txt output suits a text-only model
  4. Start the local server as -picoweb:8080:127.0.0.1. Without the bind address it listens on every interface
  5. Use npx -y @plantuml/mcp-js when no Java runtime is present. It renders SVG only, so use the jar for PNG or PDF

Questions

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

PlantUML scores 66.9 (B) on agent readiness against Diagrams.so API + MCP's 60 (C), and leads in 3 of 7 scored categories. Diagrams.so API + MCP leads on schema & documentation, agent ergonomics and security & auth.

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

Diagrams.so API + MCP has a hosted endpoint at https://api.diagrams.so/api/v2. No hosted endpoint is listed for PlantUML.

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

No open-source release is listed for Diagrams.so API + MCP. PlantUML is open source (GPL-3.0-or-later).

Other comparisons with Diagrams.so API + MCP or PlantUML

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