Is Mermaid MCP server safe?

No malicious indicators - review capabilities before installing

Notable — review in context (a capability is not a malicious indicator):

npm install-time lifecycle hook
Node.js filesystem write/delete
npm prepare hook

What to do: Nothing here argues against installing it. Grant the capabilities it lists only if you expect the tool to need them.

Mermaid MCP server is an MCP server analyzed by SkillTotal's deterministic static scanner. The scan found no malicious indicators. It can: filesystem write, install time execution and mcp tools detected — capabilities are what the code can do, not a verdict on intent. Risk score 0/100 (low).

mcp-mermaid 0.4.1

GitHub repository, read as an npm package · https://github.com/hustcc/mcp-mermaid

LOW

/ 100 risk score

Snapshot · scanned Nov 13, 2026 · mcp-mermaid@0.4.1 · engine 1.1.0 / ruleset 100

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Automated static-analysis result. It can contain false positives and false negatives, and is not a claim about the intent of Mermaid MCP server's authors. Report a false positive.

Capabilities — what this component can do (not a risk score):

filesystem writeinstall time executionmcp tools detected

Behavioral traits

How this component maps to the CSA agentic threat model. Descriptive — it never affects the risk score.

Tool surface

Tool Usage

Filesystem reach

Tool Execution Context

Supply-chain provenance risk

General Protections / Supply Chain

Findings (4)

Capabilitynpm install-time lifecycle hooknot scored · severity highST-INSTALL-NPM

package.json runs scripts automatically when the package is installed.

package.json:16

"postinstall": "playwright install --with-deps chromium"

Why it matters: Install scripts are a favorite supply-chain foothold — they execute on every machine that installs the package.

Fix: Inspect the hook command. Install-time scripts are a common supply chain execution vector; ensure they do nothing beyond a documented build step.

CapabilityNode.js filesystem write/deletenot scored · severity mediumST-FS-NODE-WRITE

The component writes or deletes files on disk.

src/server.ts:137

fs.writeFileSync(filePath, screenshot);

src/utils/render.ts:28

fs.writeFileSync(cssTmpPath, cssContent);

Why it matters: Usually legitimate, but worth confirming the paths can't be controlled by untrusted input.

Fix: Confirm which files are written/deleted and that paths cannot be influenced by untrusted input.

Capabilitynpm prepare hooknot scored · severity mediumST-INSTALL-NPM-PREPARE

package.json has a 'prepare' script (runs on git/local installs and before publishing).

package.json:14

"prepare": "husky && npm run build",

Why it matters: Usually a build step, but confirm it doesn't fetch or run remote code.

Fix: Usually a legitimate build step; confirm it only builds and does not fetch or execute remote code.

CapabilityMCP tool surface detectednot scored · severity lowST-MCP-DETECTED

An MCP tool surface (manifest or tool definitions) was found.

src/server.ts:22

const server = new McpServer(

src/server.ts:45

server.server.setRequestHandler(ListToolsRequestSchema, async () => ({

src/server.ts:49

server.server.setRequestHandler(CallToolRequestSchema, async (request) => {

src/services/sse.ts:19

const transport = new SSEServerTransport("/messages", res);

src/services/stdio.ts:5

const transport = new StdioServerTransport();

src/services/streamable.ts:20

const transport = new StreamableHTTPServerTransport({

Why it matters: Just context — review which tools it offers and their permissions.

Fix: Review the declared MCP tools and their permissions.

How attackers abuse these capabilities

Interactive labs on the attack class behind the rules above. They show the technique, not anything found in Mermaid MCP server.

Install Script lab

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How we determine this: deterministic static analysis (regex + AST), evidence-anchored, no code execution. Methodology →