MCP Doesn't Need 30 Tools: It Needs Code

Summary

Your MCP Doesn’t Need 30 Tools: It Needs Code written on August 18, 2025 I wrote a while back about why code performs better than MCP (Model Context Protocol) for some tasks. In particular, I pointed out that if you have command line tools available, agentic coding tools seem very happy to use those. In the meantime, I learned a few more things that put some nuance to this. There are a handful of challenges with CLI-based tools that are rather hard to resolve and require further examination. In this blog post, I want to present the (not so novel) idea that an interesting approach is using MCP servers exposing a single tool, that accepts programming code as tool inputs. CLI Challenges The first and most obvious challenge with CLI tools is that they are sometimes platform-dependent, version-dependent, and at times undocumented. This has meant that I routinely encounter failures when using tools on first use. A good example of this is when the tool usage requires non-ASCII string inputs. For instance, Sonnet and Opus are both sometimes unsure how to feed newlines or control characters via shell arguments. This is unfortunate but ironically not entirely unique to shell tools either. For instance, when you program with C and compile it, trailing newlines are needed. At times, agentic coding tools really struggle with appending an empty line to the end of a file, and you can find some quite impressive tool loops to work around this issue. This becomes particularly frustrating when your tool is absolutely not in the training set and uses unknown syntax. In that case, getting agents to use it can become quite a frustrating experience. Another issue is that in some agents (Claude Code in particular), there is an extra pass taking place for shell invocations: the security preflight. Before executing a tool, Claude also runs it through the fast Haiku model to determine if the tool will do something dangerous and avoid the invocation. This further slows down tool use when multi...