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When does MCP make sense vs CLI?

ejholmes.github.io

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Re: When does MCP make sense vs CLI?

#71

Post by goranmoomin »

sophiabits wrote: post #68
goranmoomin wrote: post #19

I can't believe everyone is talking about MCP vs CLI and which is superior; both are a method of tool calling, it does not matter which format the LLM uses for tool calling as long as it provides the same capabilities. CLIs might be marginably better (LLMs might have been trained on common CLIs), but MCPs have their uses (complex auth, connecting users to data sources) and in my experience if you're using any of the…

> the MCP server is automatically launched when the Agent loads that skill The main problem with this approach at the moment is it busts your prompt cache, because LLMs expect all tool definitions to be defined at the beginning of the context window. Input tokens are the main driver of inference costs and a lot of use cases aren't economical without prompt caching. Hopefully in future LLMs are trained so you can add…

> The main problem with this approach at the moment is it busts your prompt cache, because LLMs expect all tool definitions to be defined at the beginning of the context window.

TBH I'm not really sure how it works in Amp (I never actually inspected how it alters the prompts that are sent to Anthropic), but does it really matter for the LLMs to have the tool definitions at the beginning of the context window in contrast to the bottom before my next new prompt?

I mean, skills also work the same way, right? (it gets appended at the bottom, when the LLM triggers the skill) Why not MCP tooling definitions? (They're basically the same thing, no?)

Re: When does MCP make sense vs CLI?

#72

Post by goranmoomin »

jeremyjh wrote: post #54
goranmoomin wrote: post #19

I can't believe everyone is talking about MCP vs CLI and which is superior; both are a method of tool calling, it does not matter which format the LLM uses for tool calling as long as it provides the same capabilities. CLIs might be marginably better (LLMs might have been trained on common CLIs), but MCPs have their uses (complex auth, connecting users to data sources) and in my experience if you're using any of the…

No, it really matters because of the impact it has on context tokens. Reading on GH issue with MCP burns 54k tokens just to load the spec. If you use several MCPs it adds up really fast.

The impact on context tokens would be more of a 'you're holding it wrong' problem, no? The GH MCP burning tokens is an issue on the GH MCP server, not the protocol itself. (I would say that since the gh CLI would be strongly represented in the training dataset, it would be more beneficial to just use the CLI in this case though.)

I do think that we should adopt Amp's MCPs-on-skills model that I've mentioned in my original comment more (hence allowing on-demand context management).

Re: When does MCP make sense vs CLI?

#73

Post by brumar »

For personnal agents like claude code, clis are awesome.

In web/cloud based environment, giving a cli to the agent is not easy. Codemode comes to mind but often the tool is externalized anyway so mcp comes handy. Standardisation of auth makes sense in these environments too.

Re: When does MCP make sense vs CLI?

#74

Post by wenc »

MCPs (especially remote MCPs) are like a black box API -- you don't have to install anything, provision any resources, etc. You just call it and get an answer. There's a place for that, but an MCP is ultimately a blunt instrument.

CLI tools on the other hand are like precision instruments. Yes, you have to install them locally once, but after that, they have access to your local environment and can discover things on their own. There are two CLIs are particularly powerful for working with large structured data: `jq` and `duckdb` cli. I tell the agent to never load large JSON, CSV or Parquet files into context -- instead, introspect them intelligently by sampling the data with said CLI tools. And Opus 4.6 is amazing at this! It figures out the shape of the data on its own within seconds by writing "probing" queries in DuckDB and jq. When it hits a bottleneck, Opus 4.6 figures out what's wrong, and tries other query strategies. It's amazing to watch it go down rabbit holes and then recovering automatically. This is especially useful for doing exploratory data analysis in ML work. The agent uses these tools to quickly check data edge cases, and does a way more thorough job than me.

CLIs also feel "snappier" than MCPs. MCPs often have latency, whereas you can see CLIs do things in real time. There's a certain ergonomic niceness to this.

p.s. other CLIs I use often in conjunction with agents:

`showboat` (Simon Willison) to do linear walkthroughts of code.

`br` (Rust port of Beads) to create epics/stories/tasks to direct Opus in implementing a plan.

`psql` to probe Postgres databases.

`roborev` (Wes McKinney) to do automatic code reviews and fixes.

Re: When does MCP make sense vs CLI?

#75

Post by drdaeman »

This is like comparing OpenAPI and strings (that may be JSON). That is, weird, and possibly even meaningless.

MCP is formally defined in the general sense (including transport protocols), CLI is not. I mean, only specific CLIs can be defined, but a general CLI is only `(String, List String, Map Int Stream) -> PID` with no finer semantics attached (save for what the command name may imply), and transport is “whatever you can bring to make streams and PIDs work”. One has to use `("cli-tool", ["--help"], {1: stdout})` (hoping that “--help” is recognized) to know more. Or use man/info (if the CLI ships a standardized documentation), or some other document.

But in the they’re both just APIs. If the sufficient semantics is provided they both do the trick.

If immediate (first-prompt) context size is a concern, just throw in a RAG that can answer what tools (MCPs or CLIs or whatever) exist out there that could be useful for a given task, rather than pushing all the documentation (MCP or CLI docs) proactively. Or, well, fine tune so the model “knows” the right tools and how to use them “innately”.

Point is, what matters is not MCP or CLI but “to achieve X must use F [more details follow]”. MCP is just a way to write this in a structured way, CLIs don’t magically avoid this.

Re: When does MCP make sense vs CLI?

#76

Post by baq »

Remote MCP solve the distribution problem just like everyone uses web apps for everything nowadays instead of desktop apps. Local MCP servers make as much sense as local web apps.

Re: When does MCP make sense vs CLI?

#77

Post by g947o »

If the author is just using Claude Code on their own personal computer, they can do whatever they want.

As soon as there is a need to interact with the outside world in a safe, controlled manner at enterprise scale, the limitations of CLI quickly become obvious.

I wish people get more informed about a subject before they write a long blog post about it.

Re: When does MCP make sense vs CLI?

#78

Post by g947o »

tuwtuwtuwtuw wrote: post #26
ako wrote: post #18

Biggest downside of CLI for me is that it needs to run in a container. You're allowing the agent to run CLI tools, so you need to limit what it can do.

Couldn't that be solved by whitelisting specific commands?

Give it a try, and challenge yourself (or ChatGPT) to break it.

You'll quickly realize that this is not feasible.

Re: When does MCP make sense vs CLI?

#79

Post by g947o »

ejholmes wrote: post #64

Hi friends! Author here. This blew up a bit, so some words. The article title and content is intentionally provocative. It’s just to get people thinking. My real views are probably a lot more balanced. I totally get there’s a space where MCP probably does actually make sense. Particularly in areas where CLI invocation would be challenging. I think we probably could have come up with something better than MCP to fill…

"intentionally provocative"

I would almost use the words "intentionally uninformed" instead.

There are huge holes in the article (as pointed out by many comments here), and I have to wonder if you genuinely don't have enough experience with MCP to bring them up, or you intentionally omitted them to make the arguments for CLI.

Re: When does MCP make sense vs CLI?

#80

Post by mikkelam »

For me, GitHub CLI is the prime example of this. This CLI is so incredibly powerful when combined with regular command line tools. Agents know how to use head, tail, jq and so on to only extract the parts it needs.

The best selling point of CLIs is the ability to chain, transform and combine. MCP cannot do this.

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