Dependencies and Security

This page provides an overview of the dependency model and security posture for @perplexity-ai/mcp-server. It covers:

• The five runtime dependencies and their roles in the codebase
• The @modelcontextprotocol/sdk's own transitive dependency tree
• Development-only tooling
• Security-relevant design decisions across the server and its CI/CD pipelines

For package metadata, npm scripts, and the bin entry point, see Package Metadata and Scripts. For detailed dependency documentation, see Core Dependencies. For a full security discussion, see Security Architecture. For development toolchain details, see Development Tooling.

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Runtime Dependencies

The server declares five direct runtime dependencies in package.json51-57

Package	Version Constraint	Resolved	Role
@modelcontextprotocol/sdk	^1.21.1	1.27.1	MCP protocol; McpServer, transports
express	^4.21.2	4.22.1	HTTP server for HTTP mode
cors	^2.8.5	2.8.5	CORS middleware for HTTP mode
undici	^6.20.0	6.23.0	Outbound HTTP client to Perplexity API
zod	^3.25.46	3.25.76	Runtime schema validation of API responses

Minimum Node.js version: >=18 (package.json68-70).

Note: express appears both as a direct dependency (^4.21.2, used in src/http.ts) and as a transitive dependency of @modelcontextprotocol/sdk at a different major version (^5.2.1). npm resolves these independently as two separate installations.

Sources: package.json51-57 package-lock.json6-34

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Dependency-to-Source-File Map

Diagram: Runtime packages mapped to the source modules that import them

Sources: package.json51-57 package-lock.json577-616

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SDK Transitive Dependencies

@modelcontextprotocol/sdk pulls in a substantial dependency tree. The notable sub-systems are listed below.

SDK Transitive Dep	Version	Purpose within SDK
hono	^4.11.4	Web framework used in SDK's HTTP transport
@hono/node-server	^1.19.9	Node.js adapter for Hono
ajv + ajv-formats	^8.17.1 / ^3.0.1	JSON Schema validation of MCP messages
eventsource + eventsource-parser	^3.0.2 / ^3.0.0	SSE client used for streaming MCP connections
express	^5.2.1	HTTP framework within SDK (separate from app's express@4)
express-rate-limit	^8.2.1	Rate-limiting on SDK's HTTP endpoints
jose	^6.1.3	JWT/JWK operations for OAuth token verification
pkce-challenge	^5.0.0	PKCE code challenge generation for OAuth flows
zod + zod-to-json-schema	^3.25 || ^4.0	Schema definition and JSON Schema export
cross-spawn	^7.0.5	Cross-platform subprocess spawning (stdio transport)
content-type	^1.0.5	HTTP Content-Type header parsing
raw-body	^3.0.0	Raw HTTP body reading
json-schema-typed	^8.0.2	Type-safe JSON Schema definitions

Diagram: SDK internal sub-system structure

Sources: package-lock.json577-616

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Development Dependencies

Development tooling is never included in published packages. The files field in package.json30-36 explicitly limits what gets published to dist/*.js (excluding test and config files), README.md, and .claude-plugin.

Package	Version	Role
typescript	^5.9.3	TypeScript compiler (tsc)
tsx	^4.19.4	Zero-build TypeScript runner for dev scripts
vitest	^4.0.5	Test runner
@vitest/coverage-v8	^4.0.5	V8-based code coverage
shx	^0.4.0	Cross-platform shell commands (chmod +x)
@types/cors	^2.8.17	TypeScript types for cors
@types/express	^5.0.0	TypeScript types for express
@types/node	^20	TypeScript types for Node.js builtins

Sources: package.json58-67

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Security Overview

The following table summarizes the security-relevant design decisions. Detailed discussion is in Security Architecture.

Concern	Mechanism	Location
API key protection	Checked at startup; never logged; passed only as Authorization: Bearer header	src/index.ts, src/server.ts
CORS enforcement	cors() middleware with ALLOWED_ORIGINS allowlist	src/http.ts
npm publish auth	OIDC id-token permission; no static token stored	.github/workflows/publish.yml
MCP registry auth	DNS + private key; MCP_REGISTRY_PRIVATE_KEY secret extracted to temp file, then deleted	.github/workflows/publish-mcp.yml
OAuth/PKCE readiness	jose and pkce-challenge available via SDK for token-based client authentication	@modelcontextprotocol/sdk transitive deps
Outbound request isolation	undici ProxyAgent proxied through optional HTTPS proxy	src/server.ts, src/logger.ts
Log level default	PERPLEXITY_LOG_LEVEL defaults to ERROR; debug output never reaches stdout	src/logger.ts

Diagram: Security-sensitive data flows

Sources: package.json22-36 package-lock.json577-616

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Node.js Engine Requirement

The package declares "node": ">=18" in package.json68-70 This constraint is shared by most of the dependency tree. Key minimum-version drivers include:

• undici 6.x requires Node.js >=18.17
• @hono/node-server requires Node.js >=18.14.1
• vitest 4.x requires Node.js ^20.0.0 || ^22.0.0 || >=24.0.0

In CI, Node.js 20 is used (.github/workflows/test.yml .github/workflows/publish.yml). See Automated Testing Workflow for details.

Sources: package.json68-70 package-lock.json537-548 package-lock.json3722-3730