# MCP vs OpenAPI: when to expose tools via Model Context Protocol vs traditional OpenAPI

**Source:** https://promtable.com/compare/anthropic-mcp-vs-openapi

> OpenAPI is the de-facto REST API spec used by traditional integrations. MCP is the new tool-calling protocol used by LLM clients. Use OpenAPI for traditional service integration; MCP for LLM-consumable capabilities.

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OpenAPI is the de-facto REST API spec used by traditional integrations. MCP is the new tool-calling protocol used by LLM clients. Use OpenAPI for traditional service integration; MCP for LLM-consumable capabilities.

## At a glance

| Dimension | Model Context Protocol (MCP) | OpenAPI |
|---|---|---|
| Primary consumer | LLM clients (Claude Desktop, Cursor, Codex, custom agents) | Any HTTP client (apps, integrations, docs) |
| Schema format | JSON-RPC + JSON Schema | OpenAPI / JSON Schema |
| Discovery | Server lists tools / resources / prompts | Spec file enumerates endpoints |
| Transport | stdio / SSE / streamable HTTP | **HTTP** ✓ |
| Auth model | OAuth 2.1 for remote | **Various — OAuth, API keys, custom** ✓ |
| Maturity | Maturing 2024-2026 | **20+ years of ecosystem** ✓ |
| Best for | LLM tool surfaces | Traditional service-to-service integration |

## Verdict

OpenAPI remains the right choice for any traditional service integration — apps, third-party tools, internal services, public APIs. MCP is the right choice for capabilities you want LLM clients to consume — Claude Desktop tools, Cursor integrations, agent capabilities. Many internal services in 2026 expose both: an OpenAPI spec for traditional consumers and an MCP server that wraps the OpenAPI surface for LLM consumers.

## When to pick which

- **Model Context Protocol (MCP)** — LLM tool surfaces, cross-client agent capabilities.
- **OpenAPI** — Traditional service integration, public APIs, third-party tools.

## FAQ

### MCP or OpenAPI for new APIs?

Both — OpenAPI for traditional consumers, MCP for LLM consumers. They aren't mutually exclusive.

### Can MCP servers wrap OpenAPI APIs?

Yes — many MCP servers in 2026 are thin wrappers over existing OpenAPI services.

### Best for AI agent capabilities?

MCP — purpose-built for cross-client LLM tool surfaces.

## Related

- [/compare/mcp-vs-function-calling](https://promtable.com/compare/mcp-vs-function-calling)
- [/glossary/mcp](https://promtable.com/glossary/mcp)
- [/glossary/function-calling](https://promtable.com/glossary/function-calling)

*Last updated: 2026-06-01*
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