Less context
The reflex is to give the agent more context. Almost always, the right move is to cut.
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When the agent gets it wrong, the reflex is to give it more context: one more document, one more example, one more instruction. It feels like help.
It's almost always the wrong move. Context engineering isn't maximizing what the agent sees — it's curating.
Why more hurts
The model doesn't weigh context the way you do. It treats almost everything in the window with similar weight, so the noise comes in with the signal. Dump the whole repo and the instruction that matters drowns in the middle.
Three effects stacking:
- Dilution: the more you pile on, the less weight each piece carries.
- Contradiction: an old doc fighting the new one, an example pointing the opposite way from the rule — the model doesn't know which wins.
- Lost in the middle: what lands in the middle of a long context is exactly what the model ignores most.
More context isn't more information. Often it's less signal.
Pruning is the skill
The skill isn't writing the perfect prompt. It's deciding what stays out.
Give the right file, not the repo. The function, not the module. The rule that applies to this task, not the whole manual. A tight scope keeps the instruction that matters at the top of the stack, where it carries weight.
Pruning feels like you're hiding something from the agent. You are — and that's the point.
Outsource the search: sub-agents
Sometimes the task means sweeping a lot: finding where a pattern shows up across thirty files, mapping a scattered convention. The sweep is expensive in context — and almost everything it reads is disposable.
So dispatch a sub-agent. It burns its own context on the search and returns just the conclusion: the file, the line, the answer. The main context never sees the junk along the way — only the result.
It's outsourced pruning: the dirty work happens in a window you throw away.
Durable and ephemeral
Separate what lasts from what passes. A permanent rule goes in the context file or in memory — entered once, always available, out of the hot window. What belongs to the task dies with the task; don't let it settle into the conversation.
Polluting the durable layer is the most expensive prune to miss: the noise comes back every time.
Context is a budget
Treat the window as a budget, not a warehouse — everything that goes in competes for attention with everything else.
It holds across time too. A long conversation doesn't need to carry the whole path: summarize, drop the route, keep the conclusion. History is a draft; state is what matters.
Context is a budget, not a warehouse. What you take out weighs more than what you put in.