Context Thrift
Overview
Context is the budget everything else is paid from. Spend it on what changes your next action; nothing else.
Rules
- Independent calls go in one parallel block. Multiple greps, reads, status checks — batch them. Sequencing independent reads adds latency, not care.
- Read targeted. The symbol or section, not the file. Widen only when a specific question demands it.
- Delegate sweeps, keep lookups. Broad questions ("where is X handled", find-all-usages in unfamiliar territory) go to a search subagent if available — keep the conclusion, not the file dumps. Known single lookups stay direct. "The subagent is for when I don't know where things live."
- The tool is the confirmation. Never re-read a file to check an edit landed; the edit tool fails loudly. Verify outcomes with one cheap end-state check (a grep for the old token), not per-file re-reads.
- Established facts stay established. What the conversation already verified, don't re-derive. What the user already decided, don't reopen.
- Don't narrate options you won't pursue. Deliberation is for choices you might actually make.
- Enough-to-act test. If more exploration would not change your next action, exploration is over. Act.
Rationalizations
| Thought | Reality |
|---|---|
| "I'll read the whole file for context" | Read what the change touches. The question you're answering defines the lines you need. |
| "Let me just double-check my edit landed" | The tool reported success; silence is success. One end-state grep beats N re-reads. |
| "One more search to be safe" | If the result wouldn't change your action, it isn't safety — it's stalling with receipts. |
| "I'll re-verify the repo layout first" | It's in your context and was correct an hour ago. Directory trees don't rot mid-session. |
| "Careful means one call at a time" | Careful means right calls. Independent lookups in sequence is the same work, slower. |
| "I'll dispatch a subagent to be thorough" | On a 40-file repo, grep returns line-level truth faster than a subagent returns prose. Match the tool to the territory. |
Provenance: mostly predicted — Opus 4.8 baseline-passed this scenario (quotes above are its own passing-run words). fable-skills test logs, 2026-06-10.
Red Flags — stop spending
- A Read call for a file you edited this turn
- The same fact verified twice in one session
- Sequential tool calls with no data dependency between them
- An exploration step you can't name the decision for
- Whole-file reads where a grep already gave you the line numbers
