MCP Server, Built-in Tool, or Skill? A Decision Framework for the Exam
Tool Design & MCP Integration is 18% of the CCA-F, and most of it comes down to one recurring decision: which distribution mechanism fits a given capability.
A large share of Domain 2 and Domain 3 scenario questions boil down to the same underlying decision, phrased differently each time: given a capability an agent needs, should it be a built-in tool, a custom MCP server, or a Claude Code skill/slash command? The exam rewards picking the narrowest fit, not the most powerful option available.
Start with what already exists
If a first-party built-in tool already covers the need — Bash, the text editor, web search/fetch — that beats building custom infrastructure that duplicates it. This is the most commonly missed "obvious" answer: test-takers reach for MCP servers reflexively when a built-in tool would already work.
MCP server: for external systems, shared across contexts
Reach for an MCP server when the capability integrates with an external system — a database, a SaaS API, an internal service — and multiple hosts or projects need that same integration. MCP standardizes the connection so it isn't rebuilt per project. Remember the vocabulary precisely: a server exposes tools/resources/prompts, a client holds a 1:1 connection to one server, and a host (like Claude Code) coordinates multiple clients.
Skill or slash command: for workflow, not external systems
When the "capability" is really a packaged way of doing something within the project — no external system involved — a skill or slash command fits better than standing up a server. The distinguishing question the exam asks: does invocation need to be autonomous (Claude decides when it's relevant → skill) or explicit (the user types it → slash command)?
A worked scenario
"A team wants Claude Code to automatically follow a specific deployment checklist whenever it's about to run a deploy command, without the user needing to remember to invoke anything." That's autonomous invocation tied to workflow, no external system — a skill, not an MCP server, and not a slash command (the user isn't the one triggering it).
Full decision rules, including transport choice (stdio vs. Streamable HTTP) and structured-error-response design, are in the Domain 2 quick reference. Drill it with Tools & MCP practice questions.