The agent has already done useful planning when it says “roughly 75 to 130 hours.” I do not want to throw that estimate away. I want to change its units.
My forward skill takes the agent's own human-hour estimate as its starting point, converts it with coefficients derived from completed session traces, then accounts for dependencies and parallel work. The look-back is supporting calibration: it helps the conversion improve after each run.
The central conversion
Keep the estimate. Change the units.
Work size for one experienced person working alone. Keep the agent's own breakdown, range, assumptions and dependencies.
÷ 43.3Your own trace-derived coefficient — human-equivalent hours per attended agent hour.
The sum of every worker's time. Four agents running for 15 minutes is about one hour of agent labor.
→ critical pathDependencies, real parallelism and the serial gates you cannot skip.
Elapsed time from dispatch to a verified stopping point, including serial integration.
Paying it forward
Take the skills—and the coefficients.
Todd shared the seed in public, so I want to do the same with my fork. These are the complete, portable Markdown skills I currently use—not abbreviated prompts or screenshots. Each file includes the real 43.3× conversion, the 60/35/22/14/10 lines-per-hour tiers, the separate 120-lines-per-hour cleanup rate, formulas, guardrails and output templates. Copy one into a SKILL.md file wherever your agent loads skills, then replace my starting coefficients as your own actuals accumulate.
Before the work
Forward estimation
- Ask the agent for its conventional human-hour estimate.
- Preserve the task breakdown, range and dependencies.
- Cross-check the input with likely files and complexity.
- Convert each item to agent labor with trace-derived calibration.
- Model parallel work as a critical path, not a naïve division.
- Report the range, basis and uncertainty.
After the work
Look-back accounting
- Inspect the completed git range.
- Exclude generated and vendored material.
- Classify insertions by file complexity.
- Keep deletion-only cleanup separate.
- Record measured wall-clock and agent labor when available.
- Append an anonymized row to the private ledger.
Current personal coefficients
43.3×Human-equivalent hours per attended agent hour, derived from 243 anonymized work-item rows over four weeks.
- T1TrivialConfiguration and boilerplate60 lines/hr
- T2RoutineTests, documentation, simple UI and scripts35 lines/hr
- T3MediumBusiness logic, data access and integrations22 lines/hr
- T4HighArchitecture, migrations and state machines14 lines/hr
- T5SpecialistParsers, systems, cryptography and GPU work10 lines/hr
- ΔCleanupDeletion-only credit, kept separate120 lines/hr
Good enough to prioritize
From 64 hours to 1.5 was the useful result.
- Agent estimate
- 75–130 human hours
- Estimate from cost-estimate skill
- ≈64 human-equivalent hours≈1.5 total agent-labor hours
- Estimate from look-back skill
- 59.7 human-equivalent hours
- Wall-clock time
- ≈7 minutesObserved with the Grok 4.5 harness
The human-equivalent work estimate held up: about 64 hours going in versus 59.7 in the look-back.
Neither the original agent estimate nor my conversion assumed parallel execution. The ≈1.5-hour result is total agent labor, not a parallel wall-clock forecast.
The observed run used Grok 4.5. In my measurements, its prefill and decode speeds were at least 50% faster than the Codex and Claude API routes behind my coefficient, and the harness also ran work in parallel. Those unmodeled advantages help explain the ≈7-minute wall-clock.
I do not plan to model every one of those variables. Going from about 64 human-equivalent hours to about 1.5 agent-labor hours is enough for me to prioritize what can run while I walk my dog.
Credit before conclusions
The look-back idea did not originate with me.
This work was seeded by Todd Saunders’s public /cost-estimate prompt: lines of code plus complexity translated into senior-developer hours. I used it publicly on March 5, 2026 with both hours and dollar return-on-investment framing.
My current fork retires the dollar layer, keeps hours-only look-back accounting, separates agent labor from attended wall-clock, and calibrates a forward forecast against my own session ledger. Julien Barbier later built a parallel expansion of Todd’s idea; it was not the direct source of my fork.
