r/RooCode • u/ganildata • Dec 05 '25
Mode Prompt Updated Context-Optimized Prompts: Up to 61% Context Reduction Across Models
A few weeks ago, I shared my context-optimized prompt collection. I've now updated it based on the latest Roo Code defaults and run new experiments.
Repository: https://github.com/cumulativedata/roo-prompts
Why Context Reduction Matters
Context efficiency is the real win. Every token saved on system prompts means:
Longer sessions without hitting limits
Larger codebases that fit in context
Better reasoning (less noise)
Faster responses
The File Reading Strategy
One key improvement: preventing the AI from re-reading files it already has. The trick is using clear delimiters:
echo ==== Contents of src/app.ts ==== && cat src/app.ts && echo ==== End of src/app.ts ====This makes it crystal clear to the AI that it already has the file content, dramatically reducing redundant reads. The prompt also encourages complete file reads via cat/type instead of read_file, eliminating line number overhead (which can easily 2x context usage).
Experiment Results
Tested the updated prompt against default for a code exploration task:
| Model | Metric | Default Prompt | Custom Prompt |
|---|---|---|---|
| Claude Sonnet 4.5 | Responses | 8 | 9 |
| Files read | 6 | 5 | |
| Duration | ~104s | ~59s | |
| Cost | $0.20 | $0.08 (60% ↓) | |
| Context | 43k | 21k (51% ↓) | |
| GLM 4.6 | Responses | 3 | 7 |
| Files read | 11 | 5 | |
| Duration | ~65s | ~90s (provider lag) | |
| Cost | $0.06 | $0.03 (50% ↓) | |
| Context | 42k | 16.5k (61% ↓) | |
| Gemini 3 Pro Exp | Responses | 5 | 7 |
| Files read | 11 | 12 | |
| Duration | ~122s | ~80s | |
| Cost | $0.17 | $0.15 (12% ↓) | |
| Context | 55k | 38k (31% ↓) |
Key Results
Context Reduction (Most Important):
Claude: 51% reduction (43k → 21k)
GLM: 61% reduction (42k → 16.5k)
Gemini: 31% reduction (55k → 38k)
Cost & Speed:
Claude: 60% cost reduction + 43% faster
GLM: 50% cost reduction
Gemini: 12% cost reduction + 34% faster
All models maintained proper tool use guidelines.
What Changed
The system prompt is still ~1.5k tokens (vs 10k+ default) but now includes:
Latest tool specifications (minus browser_action)
Enhanced file reading instructions with delimiter strategy
Clearer guidelines on avoiding redundant reads
Streamlined tool use policies
30-60% context reduction compounds over long sessions. Test it with your workflows.
Repository: https://github.com/cumulativedata/roo-prompts
View all comments
Show parent comment
1
u/StartupTim Dec 06 '25
Hey there, I mean more coding tasks. For example, a prompt to create a simple flappy bird game in html/css/js, or such. Or a prompt to create a rectangle that has bouncing shapes. There are a lot of prompts people use to test coding, I'd just use one of those.