thelobbi Prompt Budget Preflight
Run this before calling the Agent tool. It takes under 30 seconds and prevents the most common subagent failure mode: rejection with "Prompt is too long".
Why this exists
Subagents inherit a large base context before your prompt is even appended:
- Global
~/.claude/CLAUDE.md - Project
.claude/CLAUDE.mdchain (including any rules files referenced via@) - Any auto-loaded plugin
CLAUDE.mdin the subagent'scwd MEMORY.mdand auto-memory entries- System prompts for the selected
subagent_type - Tool definitions for tools the subagent can see
In our own telemetry from one 9-spawn session:
| Spawn type | Prompt size | Result |
|---|---|---|
Explore × 2 (generic) |
~900 words each | Both rejected — "Prompt is too long", 0 tokens used, 2.3-2.7s round-trip |
| Named specialists × 7 (architecture / perf / security / dx / ux / researcher / code-reviewer) | ~200-400 words each | All 7 succeeded |
Reject rate: 22%. Every rejection is a wasted ~3 seconds and a wasted decision cycle.
The 5-section minimum-viable prompt
Target ~300 words total. If you exceed 800 words you almost certainly have dead weight.
1. TARGET
- Absolute file paths or directory scope
- Clear in/out-of-scope boundaries
2. TASK
- One sentence: what to produce
- Read-only vs write explicitly stated
3. FORMAT
- Output shape (YAML, table, bullets)
- Word ceiling or row cap
- Any required fields / schema
4. CONSTRAINTS
- What NOT to do
- Paths / patterns / subdirectories to avoid
- Word-limit enforcement hint
5. RULES (optional, only when applicable)
- Plugin-specific guardrails
- "Do not follow interview-first workflow — this is an audit"
- "Do not write files — this is analysis only"
Preflight checklist
Before each Agent call, answer:
- Subagent type: am I using a named specialist that already has the relevant system prompt, or a generic (
Explore,general-purpose)? Prefer specialists — seeskills/cc-agentic-patterns/SKILL.mdPart 4. - Prompt length: is my prompt under 500 words? If over 800, trim.
- Enumeration test: am I re-listing facts the agent can grep? If yes, drop them — say "grep for X" instead of pasting X.
- Context inheritance: will the agent spawn inside a directory whose
CLAUDE.mdis large (>4KB) and unrelated to the task? If yes, include aRULESline telling it to ignore that file's workflow prescriptions. - Output ceiling: did I specify a word ceiling and/or row cap? If no, add one.
Failure-mode playbook
| If agent rejects with… | Do this |
|---|---|
| "Prompt is too long" | Cut enumerated facts; swap generic subagent for a named specialist; add RULES line telling it to skip directory CLAUDE.md workflows |
| Empty or stub output | Prompt was too vague — add concrete file:line references and one worked example of the output shape |
| Off-topic ramble | Missing CONSTRAINTS section — add explicit "do NOT explore X / Y / Z" |
| Timeout (>5min on simple task) | Missing word ceiling + missing scope boundary — add both |
Template — copy-paste to start
You are analyzing <SCOPE>.
TARGET: <absolute paths>
TASK: <one sentence; read-only or write>
FORMAT:
<schema / shape>
Keep under <N> words.
CONSTRAINTS:
- Do not <X>
- Do not explore <Y>
RULES (if applicable):
- Ignore the <plugin-name> CLAUDE.md's interview-first workflow;
this is an audit, not a setup run.
When to skip the preflight
- Prompt is under 2 paragraphs AND the subagent type matches a named specialist.
- The task is so scoped a wrong output won't cost a retry (e.g., "find all files matching X").
Everything else: run the 5-question checklist above. It's cheaper than a rejected spawn.