MCP is the standard, but each major model has its own tool-use spec — historically and ongoing. A team building cross-provider applications needs to know the landscape.
The state of the art
MCP. Anthropic-originated; widely adopted. The standard for ecosystem tools.
Function calling (OpenAI). Predates MCP; still widely used in OpenAI-specific work. Compatible patterns; different protocol.
Tool use (Anthropic API). Anthropic's native tool-use API. MCP-compatible at the spec level.
Native function/tool calling in other providers. Each has its own variant.
Reviewer ritual
For cross-provider applications:
- Document the tool-use approach per provider.
- Plan migration if standards converge.
- Avoid lock-in to a specific provider's spec.
A real comparison
A team building tools for both Claude and ChatGPT:
- Built MCP servers (the standard).
- Wrapped MCP for ChatGPT via a translator (function-calling format).
- Native MCP for Claude.
The team's investment in MCP servers paid off. The wrapping work was straightforward.
Trade-offs
- Stick to MCP: forward-looking; some translation needed for non-MCP providers.
- Per-provider native specs: less translation; more lock-in.
The industry is converging on MCP. Lean MCP.
Limits
MCP doesn't yet cover:
- Some edge cases other specs handle differently.
- Multi-modal arguments (images in tool calls).
- Some streaming patterns.
These gaps are closing as MCP evolves.
What we won't ship
Cross-provider applications without an abstraction layer.
Lock-in to a specific provider's spec when MCP would do.
Skipping the migration plan when standards evolve.
Close
Beyond MCP, the landscape has multiple tool-use specs. MCP is the de-facto standard. Building MCP-first with provider-specific adapters where needed is the durable strategy.
Related reading
- MCP in 10 minutes — the primer.
- Why we need MCP at all — the history.
- Tool design like APIs — surrounding discipline.
We build AI-enabled software and help businesses put AI to work. If you're navigating tool-use specs, we'd love to hear about it. Get in touch.