It strikes me there's more low hanging fruit to pluck re. context window management. Backtracking strikes me as another promising direction to avoid context bloat and compaction (i.e. when a model takes a few attempts to do the right thing, once it's done the right thing, prune the failed attempts out of the context).
Agree. I’d like more fine grained control of context and compaction. If you spend time debugging in the middle of a session, once you’ve fixed the bugs you ought to be able to remove everything related to fixing them out of context and continue as you had before you encountered them. (Right now depending on your IDE this can be quite annoying to do manually. And I’m not aware of any that allow you to snip it out if you’ve worked with the agent on other tasks afterwards.)
I think agents should manage their own context too. For example, if you’re working with a tool that dumps a lot of logged information into context, those logs should get pruned out after one or two more prompts.
Context should be thought of something that can be freely manipulated, rather than a stack that can only have things appended or removed from the end.
Oh that's quite a nice idea - agentic context management (riffing on agentic memory management).
There's some challenges around the LLM having enough output tokens to easily specify what it wants its next input tokens to be, but "snips" should be able to be expressed concisely (i.e. the next input should include everything sent previously except the chunk that starts XXX and ends YYY). The upside is tighter context, the downside is it'll bust the prompt cache (perhaps the optimal trade-off is to batch the snips).
Maybe the right answer is “why not both”, but subagents can also be used for that problem. That is, when something isn’t going as expected, fork a subagent to solve the problem and return with the answer.
It’s interesting to imagine a single model deciding to wipe its own memory though, and roll back in time to a past version of itself (only, with the answer to a vexing problem)
I forget where now but I'm sure I read an article from one of the coding harness companies talking about how they'd done just that. Effectively it could pass a note to its past self saying "Path X doesn't work", and otherwise reset the context to any previous point.
I could see this working like some sort of undo tree, with multiple branches you can jump back and forth between.
It feels like the late 1990s all over again, but instead of html and sql, it’s coding agents. This time around, a lot of us are well experienced at software engineering and so we can find optimizations simply by using claude code all day long. We get an idea, we work with ai to help create a detailed design and then let it develop it for us.
The core idea: every MCP tool call dumps raw data into your 200K context window. Context Mode spawns isolated subprocesses — only stdout enters context. No LLM calls, purely algorithmic: SQLite FTS5 with BM25 ranking and Porter stemming.
Since the last post we've seen 228 stars and some real-world usage data. The biggest surprise was how much subagent routing matters — auto-upgrading Bash subagents to general-purpose so they can use batch_execute instead of flooding context with raw output.
Really intrigued and def will try, thanks for this.
In connecting the dots (and help me make sure I'm connecting them correctly), context-mode _does not address MCP context usage at all_, correct? You are instead suggesting we refactor or eliminate MCP tools, or apply concepts similar to context_mode in our MCPs where possible?
Context-mode is still very high value, even if the answer is "no," just want to make sure I understand. Also interested in your thoughts about the above.
I write a number of MCPs that work across all Claude surfaces; so the usual "CLI!" isn't as viable an answer (though with code execution it sometimes can be) ...
Do you need 80+ tools in context? Even if reduced, why not use sub agents for areas of focus? Context is gold and the more you put into it unrelated to the problem at hand the worse your outcome is. Even if you don't hit the limit of the window. Would be like compressing data to read into a string limit rather than just chunking the data
This sounds a little bit like rkt? Which trims output from other CLI applications like git, find and the most common tools used by Claude. This looks like it goes a little further which is interesting.
I see some of these AI companies adopting some of these ideas sooner or later. Trim the tokens locally to save on token usage.
AFAIK Claude Code doesn't inject all the MCP output into the context. It limits 25k tokens and uses bash pipe operators to read the full output. That's at least what I see in the latest version.
I've seen a few projects like this. Shouldn't they in theory make the llms "smarter" by not polluting the context? Have any benchmarks shown this effect?
Excited to try this. Is this not in effect a kind of "pre-compaction," deciding ahead of time what's relevant? Are there edge cases where it is unaware of, say, a utility function that it coincidentally picks up when it just dumps everything?
The 98% reduction is the real story here, but the systemic problem you're solving is even bigger than individual tool calls blowing up context. When you're orchestrating multi-step workflows, each tool output becomes part of the conversation state that carries forward to the next step. A Playwright snapshot at step 1 is 56 KB. It still counts at step 3 when you've moved on to something completely different.
The subprocess isolation is smart - stdout-only is the right constraint. I've been running multi-agent workflows where the cost of tool output accumulation forces you to make bad decisions: either summarise outputs manually (defeating the purpose of tool calls), truncate logs (information loss), or cap the workflow depth. None of them good.
The search ranking piece is worth noting. Most people just grep logs or dump chunks and let the LLM sort it out. BM25 + FTS5 means you're pre-filtering at index time, not letting the model do relevance ranking on the full noise. That's the difference between usable and unusable context at scale.
Only question: how does credential passthrough work with MCP's protocol boundaries? If gh/aws/gcloud run in the subprocess, how does the auth state persist between tool calls, or does each call reinit?
No magic — standard Unix process inheritance. Each execute() spawns a child process via Node's child_process.spawn() with a curated env built by #buildSafeEnv (https://github.com/mksglu/claude-context-mode/blob/main/cont...). It passes through an explicit allowlist of auth vars (GH_TOKEN, AWS_ACCESS_KEY_ID, GOOGLE_APPLICATION_CREDENTIALS, KUBECONFIG, etc.) plus HOME and XDG paths so CLI tools find their config files on disk. No state persists between calls — each subprocess inherits credentials from the MCP server's environment, runs, and exits. This works because tools like gh and aws resolve auth on every invocation anyway (env vars or ~/.config files). The tradeoff is intentional: allowlist over full process.env so the sandbox doesn't leak unrelated vars.
Nice work.
It strikes me there's more low hanging fruit to pluck re. context window management. Backtracking strikes me as another promising direction to avoid context bloat and compaction (i.e. when a model takes a few attempts to do the right thing, once it's done the right thing, prune the failed attempts out of the context).
Agree. I’d like more fine grained control of context and compaction. If you spend time debugging in the middle of a session, once you’ve fixed the bugs you ought to be able to remove everything related to fixing them out of context and continue as you had before you encountered them. (Right now depending on your IDE this can be quite annoying to do manually. And I’m not aware of any that allow you to snip it out if you’ve worked with the agent on other tasks afterwards.)
I think agents should manage their own context too. For example, if you’re working with a tool that dumps a lot of logged information into context, those logs should get pruned out after one or two more prompts.
Context should be thought of something that can be freely manipulated, rather than a stack that can only have things appended or removed from the end.
Oh that's quite a nice idea - agentic context management (riffing on agentic memory management).
There's some challenges around the LLM having enough output tokens to easily specify what it wants its next input tokens to be, but "snips" should be able to be expressed concisely (i.e. the next input should include everything sent previously except the chunk that starts XXX and ends YYY). The upside is tighter context, the downside is it'll bust the prompt cache (perhaps the optimal trade-off is to batch the snips).
Maybe the right answer is “why not both”, but subagents can also be used for that problem. That is, when something isn’t going as expected, fork a subagent to solve the problem and return with the answer.
It’s interesting to imagine a single model deciding to wipe its own memory though, and roll back in time to a past version of itself (only, with the answer to a vexing problem)
I forget where now but I'm sure I read an article from one of the coding harness companies talking about how they'd done just that. Effectively it could pass a note to its past self saying "Path X doesn't work", and otherwise reset the context to any previous point.
I could see this working like some sort of undo tree, with multiple branches you can jump back and forth between.
It feels like the late 1990s all over again, but instead of html and sql, it’s coding agents. This time around, a lot of us are well experienced at software engineering and so we can find optimizations simply by using claude code all day long. We get an idea, we work with ai to help create a detailed design and then let it develop it for us.
Author here. I shared the GitHub repo a few days ago (https://news.ycombinator.com/item?id=47148025) and got great feedback. This is the writeup explaining the architecture.
The core idea: every MCP tool call dumps raw data into your 200K context window. Context Mode spawns isolated subprocesses — only stdout enters context. No LLM calls, purely algorithmic: SQLite FTS5 with BM25 ranking and Porter stemming.
Since the last post we've seen 228 stars and some real-world usage data. The biggest surprise was how much subagent routing matters — auto-upgrading Bash subagents to general-purpose so they can use batch_execute instead of flooding context with raw output.
Source: https://github.com/mksglu/claude-context-mode Happy to answer any architecture questions.
Really intrigued and def will try, thanks for this.
In connecting the dots (and help me make sure I'm connecting them correctly), context-mode _does not address MCP context usage at all_, correct? You are instead suggesting we refactor or eliminate MCP tools, or apply concepts similar to context_mode in our MCPs where possible?
Context-mode is still very high value, even if the answer is "no," just want to make sure I understand. Also interested in your thoughts about the above.
I write a number of MCPs that work across all Claude surfaces; so the usual "CLI!" isn't as viable an answer (though with code execution it sometimes can be) ...
Edit: typo
Do you need 80+ tools in context? Even if reduced, why not use sub agents for areas of focus? Context is gold and the more you put into it unrelated to the problem at hand the worse your outcome is. Even if you don't hit the limit of the window. Would be like compressing data to read into a string limit rather than just chunking the data
This sounds a little bit like rkt? Which trims output from other CLI applications like git, find and the most common tools used by Claude. This looks like it goes a little further which is interesting.
I see some of these AI companies adopting some of these ideas sooner or later. Trim the tokens locally to save on token usage.
https://github.com/rtk-ai/rtk
AFAIK Claude Code doesn't inject all the MCP output into the context. It limits 25k tokens and uses bash pipe operators to read the full output. That's at least what I see in the latest version.
I did this accidentally while porting Go to IRIX: https://github.com/unxmaal/mogrix/blob/main/tools/knowledge-...
I've seen a few projects like this. Shouldn't they in theory make the llms "smarter" by not polluting the context? Have any benchmarks shown this effect?
Excited to try this. Is this not in effect a kind of "pre-compaction," deciding ahead of time what's relevant? Are there edge cases where it is unaware of, say, a utility function that it coincidentally picks up when it just dumps everything?
I am a happy user of this and have recommended my team also install it. It’s made a sizable reduction in my token use.
this is going to crash the AI economy. nvda down 20 percent monday. lol
The 98% reduction is the real story here, but the systemic problem you're solving is even bigger than individual tool calls blowing up context. When you're orchestrating multi-step workflows, each tool output becomes part of the conversation state that carries forward to the next step. A Playwright snapshot at step 1 is 56 KB. It still counts at step 3 when you've moved on to something completely different.
The subprocess isolation is smart - stdout-only is the right constraint. I've been running multi-agent workflows where the cost of tool output accumulation forces you to make bad decisions: either summarise outputs manually (defeating the purpose of tool calls), truncate logs (information loss), or cap the workflow depth. None of them good.
The search ranking piece is worth noting. Most people just grep logs or dump chunks and let the LLM sort it out. BM25 + FTS5 means you're pre-filtering at index time, not letting the model do relevance ranking on the full noise. That's the difference between usable and unusable context at scale.
Only question: how does credential passthrough work with MCP's protocol boundaries? If gh/aws/gcloud run in the subprocess, how does the auth state persist between tool calls, or does each call reinit?
No magic — standard Unix process inheritance. Each execute() spawns a child process via Node's child_process.spawn() with a curated env built by #buildSafeEnv (https://github.com/mksglu/claude-context-mode/blob/main/cont...). It passes through an explicit allowlist of auth vars (GH_TOKEN, AWS_ACCESS_KEY_ID, GOOGLE_APPLICATION_CREDENTIALS, KUBECONFIG, etc.) plus HOME and XDG paths so CLI tools find their config files on disk. No state persists between calls — each subprocess inherits credentials from the MCP server's environment, runs, and exits. This works because tools like gh and aws resolve auth on every invocation anyway (env vars or ~/.config files). The tradeoff is intentional: allowlist over full process.env so the sandbox doesn't leak unrelated vars.
Two LLMs speaking with each other on HN? Amusing!
Why are you assuming they’re an LLM? And please don’t say “em dash”.
Note: you’re replying to the library’s author.
The first two sentences of the first two paragraphs of OP are a dead giveaway.