Compare the total cost of car ownership across buy-new, buy-used, lease, and keep-your-current-car — depreciation, insurance, maintenance ramp, and fuel over a real horizon, not just the monthly payment.
SkillScore95Maintained
Automatic
◆Finance & Accounting pack
Last verified 8/14/2026
What it changes
Passed 21 of 22 test cases with the skill, and 15 of 22 without it.
Without skill68%
With skill95%
Checks it passed that the model alone missed
Uses $0.14 per mile as the default fuel cost
Lists financing interest as an excluded factor
Lists financing interest as a non-modeled factor
and 6 more in the full report
7 fixed14 passed either way0 still failing1 broke
Pass-rate lift
+27 pp
Tokens
+35%
Agent turns
0%
Response time
-6%
Model gemini-3.6-flashMeasured 8/14/2026v121 of 22 cases passed with skill
Tokens, turns and time describe resource use, not a dollar price.
See it in action
One of 7 test cases the skill fixed. Same model, same prompt, with and without the skill.
1 of 7
Prompt
My 10-year-old vehicle needs $2,200 in repairs this year. A new replacement vehicle costs $34,000. Is spending $2,200 on repairs financially unwise?
What was checked, without and with the skill
Checked
Without skill
With skill
Compares the $2,200 repair cost against first-year depreciation on the replacement vehicle
Missed
Passed
Frames maintaining the existing car as potentially cheaper than replacement car depreciation
Passed
Passed
case-08 · gemini-3.6-flash · 8/14/2026 · answers are capped and redacted
What's inside
The instructions your model reads when the skill loads.
SKILL.md69 lines3 filesincludes scripts
Car TCO Skill
Cars are sold on monthly payments and owned on total cost — and the two rank options differently. Depreciation (the biggest cost of a new car) never appears on a statement; maintenance (the biggest fear about an old car) is usually smaller than a year of new-car depreciation. This skill compares buy-new, buy-used, lease-forever, and keep-current on the same total-cost basis over the same horizon.
What This Skill Produces
Ranked scenario totals — every requested scenario over the same horizon, cheapest first
True per-month cost — total ÷ months, the number to compare against the payment the dealer quotes
The assumption ledger — depreciation curve, maintenance ramp, insurance deltas, all labeled
The not-modeled list — financing interest, jurisdiction taxes, reliability luck
Required Inputs
Ask for these if not provided:
Which scenarios to compare — any of: new price, used-equivalent price, lease terms, current car's value + annual maintenance
Horizon — years they realistically keep cars (default 8, labeled); short horizons flatter leasing, long ones flatter buying
Miles per year and rough fuel/energy cost (defaults 12,000 mi / $0.14 per mile, labeled)
Deterministic. Depreciation: 20% year one then 10%/yr for new, gentler for used/current. Maintenance ramps 8%/yr (used cars start further up the ramp). Leases re-lease at each term end with a fresh drive-off. Resale value is credited back — TCO is what you spent minus what you can recover.
Framework: The Payment Illusion Rules
Depreciation is the invisible line item — a new car's largest cost has no bill; it's the resale-value credit shrinking
"My old car needs $2,000 of work" is usually cheap — compare the repair to a year of the replacement's depreciation before calling it "not worth fixing"
Leasing buys flexibility, not savings — lease-forever means paying peak depreciation years forever; price that honestly and let people buy flexibility knowingly
Margins under ~10% are noise — the model's assumptions can't resolve differences that small; say "roughly a tie," not a winner
The horizon drives the ranking — always name it; the same inputs rank differently at 3 years vs 10