MCP, REST, and a CLI are three interfaces to a social publishing system. They do not define three different reliability models. A strong product keeps account boundaries, confirmation, idempotency, state, and errors consistent across all three.
The useful choice is which interface best fits the client and moment.
Quick comparison
| Interface | Strongest fit | Main advantage | Main tradeoff |
|---|---|---|---|
| MCP | Interactive agents and tool-aware clients | Tool discovery and typed inputs inside the agent session | Client support and tool trust still vary |
| REST API | Services, integrations, and durable automation | Stable transport contract with broad language support | The client must implement discovery, auth, and orchestration |
| CLI | Coding agents, terminals, scripts, and debugging | Fast human-readable use with shell composition | Process output and local credential handling need discipline |
Choose MCP for in-session tool discovery
An MCP client can discover schema-defined tools, inspect their arguments, and call them without teaching the model a custom HTTP request format. This is useful when a coding or general-purpose agent needs to move between several products in one session.
MCP annotations can describe properties such as read-only or idempotent behavior. They are hints, not enforcement. The service still has to authenticate the caller, authorize the Workspace, require confirmation where appropriate, and implement the behavior it describes.
Choose REST for durable product integrations
REST is the broadest fit for background services, CI jobs, internal tools, and integrations that need explicit request and response control. OpenAPI can provide machine-readable discovery, client generation, and a stable reference for humans and agents.
REST is also the clearest place to expose transport details such as HTTP status, ETags, idempotency keys, retry headers, pagination, and webhook configuration. That makes it valuable as the underlying contract even when MCP or a CLI is the normal client.
Choose a CLI for coding-agent and operator workflows
A CLI is useful when the agent already works in a repository or terminal. It can read a file, prepare a command, show a diff or preview, and return structured output without writing a custom integration.
The CLI should support machine-readable output and predictable exit codes. It should avoid printing secrets and should preserve the same confirmation and retry rules as the API. A successful local process only proves that the command completed. It should still return the remote Post state and provider evidence.
Use more than one without creating three products
A practical architecture is:
- One versioned publishing domain and state machine.
- One authorization and confirmation policy.
- One stable error and receipt model.
- REST as the transport contract.
- A CLI and MCP server as faithful clients of that contract.
This lets a person debug with the CLI, a service automate with REST, and an agent discover tools through MCP without changing the meaning of a Post.
The decision rule
Use MCP when discovery inside an agent client matters most. Use REST when a durable integration owns the workflow. Use a CLI when the workflow already lives in a terminal or repository. Evaluate the product underneath all three with the same production-readiness checklist.
For OpenPMM’s current hosted MCP, API, and CLI model, see Agents CLI and API and CLI publishing. The hosted MCP server uses browser-based OAuth and exposes the same public publishing contract as the API and CLI.