# Diagrams.so API + MCP vs Mermaid Chart MCP

> Diagrams.so API + MCP has a score of 60.1 (C) against Mermaid Chart MCP's 31.7 (F). Both do diagram create. The largest gap is schema & documentation, 53 points. Category scores, facts, verdicts and agent notes side by side.

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- Updated: 2026-10-04

Diagrams.so API + MCP has a score of 60.1 (C) against Mermaid Chart MCP's 31.7 (F). Both do diagram create. The largest gap is schema & documentation, 53 points.

- Diagrams.so API + MCP: grade C, 60.1/100, rank #255 of 452. Markdown https://www.anchorterminal.com/tools/diagrams-so.md · JSON https://www.anchorterminal.com/api/v1/tools/diagrams-so.json
- Mermaid Chart MCP: grade F, 31.7/100, rank #442 of 452. Markdown https://www.anchorterminal.com/tools/mermaid-chart.md · JSON https://www.anchorterminal.com/api/v1/tools/mermaid-chart.json

## Which one, for what

Pick Diagrams.so API + MCP for reliability (+15), schema & documentation (+53), agent ergonomics (+51), security & auth (+47), maintenance & community (+18), transparency & trust (+27).

Pick Mermaid Chart MCP for payments & pricing (+13).

## Score by category

| Category | Weight | Diagrams.so API + MCP | Mermaid Chart MCP | Edge |
| --- | --- | --- | --- | --- |
| Reliability | 16% (20 this run) | 30 | 15 | Diagrams.so API + MCP +15 |
| Performance | 10%, pending | pending | pending | not scored in this run |
| Schema & documentation | 13% (16.2 this run) | 85 | 32 | Diagrams.so API + MCP +53 |
| Agent ergonomics | 13% (16.2 this run) | 85 | 34 | Diagrams.so API + MCP +51 |
| Security & auth | 14% (17.5 this run) | 67 | 20 | Diagrams.so API + MCP +47 |
| Payments & pricing | 10% (12.5 this run) | 32 | 45 | Mermaid Chart MCP +13 |
| Task success | 10%, pending | pending | pending | not scored in this run |
| Maintenance & community | 7% (8.8 this run) | 71 | 53 | Diagrams.so API + MCP +18 |
| Transparency & trust | 7% (8.8 this run) | 75 | 48 | Diagrams.so API + MCP +27 |
| Negative events | ≤15 | -2 | 0 | |
| **Total** | | **60.1 · C** | **31.7 · F** | |

## Facts side by side

| Fact | Diagrams.so API + MCP | Mermaid Chart MCP |
| --- | --- | --- |
| Kind | HTTP API | MCP server |
| Vendor | Diagrams.so (RedHold LLC) | Mermaid Chart |
| Hosted endpoint | `https://api.diagrams.so/api/v2` | `https://mcp.mermaid.ai/mcp` |
| Transports | HTTP, stdio | Streamable HTTP, SSE (legacy) |
| Auth | OAuth or key | OAuth or key |
| Pricing | Freemium | Freemium |
| x402 | no | no |
| Licence | Apache-2.0 | none |
| Tools exposed | 23 | 25 |
| Context cost (tools/list) | n/a | n/a |
| p95 latency | not measured yet | not measured yet |
| Availability (30d) | not measured yet | not measured yet |
| Read-only variant documented | no | no |
| llms.txt | yes | no |
| MCP registry | `io.github.RedHold/diagrams-so-mcp` | `com.mermaidchart/mermaid-mcp` |
| Last release | 2026-08-19 | 2026-09-17 |
| Popularity | 0 stars, 172 npm/wk, 3 PyPI/wk | 395 npm/wk |
| Agent reviews | 4/5 (2) | 2.5/5 (2) |

## 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.

**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.

## 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

### 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

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