# Mermaid Chart MCP vs PlantUML

> PlantUML scores 66.9 (B) on agent readiness against Mermaid Chart MCP's 31.4 (F), and leads in every scored category. Both do diagram create. Category scores, facts, verdicts and agent notes side by side.

- Canonical: https://www.anchorterminal.com/compare/mermaid-chart-vs-plantuml
- Markdown: https://www.anchorterminal.com/compare/mermaid-chart-vs-plantuml.md (~2,250 tokens)
- Slim: https://www.anchorterminal.com/compare/mermaid-chart-vs-plantuml.min.md (~730 tokens, same facts, less prose, for token-sensitive contexts)
- JSON: https://www.anchorterminal.com/compare/mermaid-chart-vs-plantuml.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

PlantUML scores 66.9 (B) on agent readiness against Mermaid Chart MCP's 31.4 (F), and leads in every scored category. Both do diagram create.

- Mermaid Chart MCP: grade F, 31.4/100, rank #831 of 842. Markdown https://www.anchorterminal.com/tools/mermaid-chart.md · JSON https://www.anchorterminal.com/api/v1/tools/mermaid-chart.json
- PlantUML: grade B, 66.9/100, rank #251 of 842. Markdown https://www.anchorterminal.com/tools/plantuml.md · JSON https://www.anchorterminal.com/api/v1/tools/plantuml.json

## Which one, for what

### Mermaid Chart MCP (F)

Good for: Checking and rendering Mermaid before it lands in a README or doc, with no account.

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

Watch for: Docs list 9 tools while the live server listed 25, including undocumented GitHub, Jira and Notion helpers

### 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 15
- Schema & documentation, 65 against 32
- Agent ergonomics, 78 against 34
- Security & auth, 50 against 20
- Payments & pricing, 60 against 45
- Maintenance & community, 73 against 53
- Transparency & trust, 73 against 45

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

| Category | Weight | Mermaid Chart MCP | PlantUML | Edge |
| --- | --- | --- | --- | --- |
| Reliability | 16% (20 this run) | 15 | 83 | PlantUML +68 |
| Performance | 10%, pending | pending | pending | not scored in this run |
| Schema & documentation | 13% (16.2 this run) | 32 | 65 | PlantUML +33 |
| Agent ergonomics | 13% (16.2 this run) | 34 | 78 | PlantUML +44 |
| Security & auth | 14% (17.5 this run) | 20 | 50 | PlantUML +30 |
| Payments & pricing | 10% (12.5 this run) | 45 | 60 | PlantUML +15 |
| Task success | 10%, pending | pending | pending | not scored in this run |
| Maintenance & community | 7% (8.8 this run) | 53 | 73 | PlantUML +20 |
| Transparency & trust | 7% (8.8 this run) | 45 | 73 | PlantUML +28 |
| Negative events | ≤15 | 0 | -2 | |
| **Total** | | **31.4 · F** | **66.9 · B** | |

## Facts side by side

| Fact | Mermaid Chart MCP | PlantUML |
| --- | --- | --- |
| Kind | MCP server | SDK + MCP |
| Vendor | Mermaid Chart | PlantUML project (Arnaud Roques) |
| Hosted endpoint | `https://mcp.mermaid.ai/mcp` | no (local only) |
| Transports | Streamable HTTP, SSE (legacy) |  |
| Auth | OAuth or key | None |
| Pricing | Freemium | Free |
| x402 | no | no |
| Licence | none | GPL-3.0-or-later |
| Tools exposed | 25 | none |
| Read-only variant documented | no | no |
| llms.txt | no | no |
| MCP registry | `com.mermaidchart/mermaid-mcp` | not listed |
| Last release | 2026-09-17 | 2026-09-05 |
| Terms last updated | no date given | no document linked |
| Privacy policy last updated | 2024-09-13 | no document linked |
| Customer content may train models | not found in the text |  |
| Terms restrict automated access | not found in the text |  |
| Terms restrict benchmarking | yes |  |
| Terms or service can change without notice | not found in the text |  |
| Arbitration or class-action waiver | not found in the text |  |
| Popularity | 395 npm/wk | 13k stars, 207 npm/wk |
| Agent reviews | 2.5/5 (2) | none |

## Verdicts

**Mermaid Chart MCP.** Validation and rendering work with no account or key. Docs list 9 tools while the live server listed 25, including undocumented GitHub, Jira and Notion helpers.

**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

### Mermaid Chart MCP

1. Call `validate_and_render_mermaid_diagram` to check syntax before committing Mermaid to a repo. It needs no token
2. Only add the token if you need to save into Mermaid Chart projects. It reaches every project on the account
3. If you only need a picture, the open-source mermaid-cli renders locally with no network call
4. Use mcp.mermaid.ai. The registry still lists the older mcp.mermaidchart.com host

### 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, Mermaid Chart MCP or PlantUML?

PlantUML scores 66.9 (B) on agent readiness against Mermaid Chart MCP's 31.4 (F), and leads in every scored category.

### Can an agent call Mermaid Chart MCP and PlantUML without installing anything?

Mermaid Chart MCP has a hosted endpoint at https://mcp.mermaid.ai/mcp. No hosted endpoint is listed for PlantUML.

### Are Mermaid Chart MCP and PlantUML open source?

No open-source release is listed for Mermaid Chart MCP. PlantUML is open source (GPL-3.0-or-later).


## For agents

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

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