Cost Benefit

Only stop to ask the user when: project description is missing, there are fewer than 2 options (including do-nothing), or cost / benefit magnitudes cannot be estimated. Never stop to ask about: perspective, additionality rates, stakeholder tagging, sensitivity method, output filename, or formatting. Pick sensible defaults and keep moving.

Before starting, run this silently. If it outputs UPDATE_AVAILABLE, tell the user: "A new version of econstack is available. Run cd ~/.claude/skills/econstack && git pull to update." Then continue with the skill normally.

~/.claude/skills/econstack/bin/econstack-update-check 2>/dev/null || true

After the update check, run this silently to load prior learnings for this project:

eval "$(~/.claude/skills/econstack/bin/econstack-slug)"
~/.claude/skills/econstack/bin/econstack-learnings-read --limit 3 2>/dev/null || true

If learnings are found, apply them. When a prior learning influences a decision, note: "Prior learning applied: [key]".

Capturing new learnings: After completing this skill, log new insights via:

~/.claude/skills/econstack/bin/econstack-learnings-log '{"skill":"...","type":"...","key":"...","insight":"...","confidence":N,"source":"observed|user-stated|inferred"}'

Types: framework (preferred appraisal framework), parameter (custom overrides), data-source (preferred data), output (past report references), operational (tool/env quirks), preference (formatting/style). Confidence: 9-10 observed/stated, 6-8 strong inference, 4-5 weak. User-stated never decays; observed/inferred lose 1 point per 30 days. All data stored locally. Nothing transmitted.

After the update check, verify the parameter database is available and check staleness:

PARAMS_DIR="$HOME/econstack-data/parameters"
if [ -d "$PARAMS_DIR" ]; then
  PARAM_COUNT=$(find "$PARAMS_DIR" -name "*.json" 2>/dev/null | wc -l | tr -d ' ')
  echo "PARAMS: $PARAM_COUNT files loaded from $PARAMS_DIR"

  # Check for stale files (last_verified > 2 years ago)
  STALE=$(find "$PARAMS_DIR" -name "*.json" -mtime +730 2>/dev/null | wc -l | tr -d ' ')
  if [ "$STALE" -gt 0 ]; then
    echo "PARAMS_WARNING: $STALE file(s) not updated in 2+ years. Run: cd ~/econstack-data && git pull"
  fi
else
  echo "PARAMS: not found. Using built-in defaults. For full parameter support: git clone https://github.com/charlescoverdale/econstack-data.git ~/econstack-data"
fi

If PARAMS_WARNING appears, tell the user which parameter files may be stale and recommend updating. Continue with the skill normally using whatever parameters are available.

Safety rules for this skill:

1. Parameter database is read-only. Never write to, modify, or delete files in ~/econstack-data/parameters/. These are shared, versioned parameters maintained separately. If a parameter needs updating, tell the user to update the econstack-data repo.

2. Confirm before overwriting. Before writing an output file, check if a file with the same name already exists. If it does, ask the user: "A file named [filename] already exists. Overwrite it, or save with a new name?" Do not silently overwrite.

At the end of every skill run, report one of these statuses:

• DONE: Analysis complete, output generated, all sections finished.
• DONE_WITH_CONCERNS: Output generated but with caveats (e.g., data gaps, assumptions that need review, sections below expected depth).
• BLOCKED: Cannot proceed (e.g., missing critical input, parameter database unavailable, framework not supported).
• NEEDS_CONTEXT: Need more information from the user before continuing.

Format: STATUS: [status] | [one-line reason]

/cost-benefit: Cost-Benefit Analysis

Produces a Green Book-style economic case (NPV, BCR, optimism bias, sensitivity) alongside a parallel financial case (cash flow to the sponsor, Financial NPV, payback, DSCR if debt is involved), with a one-line headline verdict telling you whether the project is socially worthwhile and financially self-sustaining.

/longlist       = "Brainstorm benefits and costs"
     ↓
/cost-benefit   = "Now monetise and compute NPV"     (this skill)
     ↓
/business-case  = "Wrap in the Five Case Model"

Default output: one clean deliverable with headline verdict, options, costs, benefits, economic case, financial case, sensitivity, and recommendation. Power users can grab just one section via --section.

Arguments

/cost-benefit [project description] [options]

Examples:

/cost-benefit "New secondary school in Leeds, GBP 40m capex, 60-year appraisal"
/cost-benefit --from longlist-italy-city-greening-2026-04-10.md
/cost-benefit "Rural water project, Indonesia" --framework adb
/cost-benefit "Victorian level crossing removal" --framework au-vic

Options:

• --framework <name> : uk-gb (default), eu-brg, wb, adb, or au-vic. Auto-detected from context if not set.
• --from <file.md> : Import project, options, costs, benefits, and Cash flow tags from a /longlist markdown file. Skips the interactive entry.
• --sponsor <type> : government (default), private, blended, philanthropic. Drives the financial case discount rate. Carried through from the longlist if --from is used.
• --section <name> : Emit only one sub-component. Options: full (default), headline, costs, benefits, economic, financial, sensitivity, stakeholder, validation. Combinable with commas.
• --format <type> : Output format(s). markdown (default, always generated), xlsx, word, pptx, pdf, or all. Comma-separate for multiple.
• --distributional : Apply Green Book Annex A4 iso-elastic welfare weights (eta = 1.3, reference = median equivalised income). Silent if not set.
• --stage <name> : soc (Strategic Outline Case), obc (Outline Business Case, default), fbc (Full Business Case). Drives the optimism bias uplift.
• --ob-mitigation <pct> : Optimism bias mitigation factor in [0, 1]. Default 0. Use 0.3 to 0.5 once an active risk register is in place. Greenbook: gb_apply_ob(mitigation = ...).
• --price-base <year> : Price base year for real-terms rebasing. Default = current calendar year. All cash inputs are re-based via gb_rebase() before discounting. Greenbook: gb_deflator() / gb_real() / gb_rebase().
• --carbon-scenario <name> : low / central (default) / high. Pulls from the consolidated DESNZ Nov-2023 series. Greenbook: gb_carbon_value().
• --schedule <name> : standard (default), health (1.5% baseline for QALY/WELLBY-monetised consequences only), catastrophic (3.0% for projects where catastrophic risk dominates). Greenbook: gb_stpr(schedule = ...).
• --horizon <years> : Override the default appraisal period (60 infrastructure / 30 programmes / 10 IT). For horizons > 30 years the kinked STPR schedule kicks in automatically.
• --cea : Cost-effectiveness mode. When monetisation of the dominant benefit is impossible (low-monetisability flag from /longlist), replaces BCR with cost per output unit. Greenbook: gb_cost_per_unit().
• --audit / --no-audit : Auto-run /econ-audit on the produced markdown at the end. Default: --audit.
• --validate-only : Run the validation gate against the longlist + parameters and exit with a structured report. No NPV produced. Useful in CI.

Supported frameworks

Auto-detection rules:

• "HVHR", "Victorian", "Melbourne", AUD context → au-vic
• "ADB", Asian DMC context → adb
• "World Bank", "IBRD", "IDA" → wb
• "EU", "regulation", "directive", EUR context → eu-brg
• Everything else → uk-gb

Instructions

Step 0: Detect computation backend (silent)

Check whether the greenbook R package is reachable through the bridge script:

GB_VERSION="$(echo '{"action":"version"}' | ~/.claude/skills/econstack/bin/econstack-greenbook 2>/dev/null)"
GB_OK="$(echo "$GB_VERSION" | python3 -c 'import sys, json; d=json.loads(sys.stdin.read() or "{}"); print("yes" if d.get("ok") else "no")' 2>/dev/null || echo "no")"

• If GB_OK=yes: set BACKEND=greenbook. Use the bridge for NPV / BCR / discount factors / OB / METB / VPF / QALY / WELLBY / EANC / carbon. Stash the data_versions array for the KEY NUMBERS block. All numerical claims should match gb_economic_case() to within ±0.01.
• If GB_OK=no: set BACKEND=skill. Compute internally using the formulas below. Add a footnote to the output: "Computed without greenbook backend; install with install.packages('greenbook') or set GREENBOOK_DEV_PATH for full reproducibility and vintage stamping."

Do not narrate the backend choice to the user unless they ask. Continue with Step 1.

Step 1: Load project, options, costs, and benefits

If --from <file.md> specified: read the longlist markdown file and parse:

• Project name and counterfactual from the header block
• Framework and sponsor from the header block (default if missing)
• Benefits table: for each item, capture Name, Description, Materiality, Cash flow tag, Quantification method, Monetisation method
• Costs table: same six columns
• Excluded section (note for reference but do not include in NPV)

Skip the interactive entry and proceed to Step 2.

Otherwise: ask the user in ONE AskUserQuestion batch:

1. Project: one or two sentences (what, where, why).
2. Options: the alternatives being compared. Must include "Do nothing" (the counterfactual). Typically 3 options: do nothing, do minimum, preferred.
3. Costs: total capital (phased over how many years) and annual operating cost. If an estimate doesn't exist, ask for a range and mark the field as "Estimated".
4. Benefits: annual benefit at maturity, plus benefit type (e.g. "health QALYs", "user time savings", "avoided flood damage").

Do NOT ask perspective, referent group, distributional weights, sensitivity method, appraisal period, optimism bias rate, or discount rate. Detect sector from the description. Default:

• Appraisal period: 60 years (infrastructure), 30 years (programmes), 10 years (IT). Override with --horizon.
• Optimism bias: HMT supplementary Table 1 for the detected project type and stage. Mitigation factor 0 unless --ob-mitigation is set.
• Additionality: 20% deadweight, 25% displacement, 10% leakage (net factor 0.54) unless user provides different values.
• Perspective: social / national for government sponsors; investor for private sponsors.
• Referent group: all residents of the host country (or region for au-vic).
• Price base year: current calendar year unless --price-base overrides. Real-terms rebasing applied to all cash inputs before discounting (uk-gb only; greenbook gb_rebase()).
• Schedule: standard for the main appraisal. The health schedule is applied only to QALY / WELLBY benefit lines; do not apply 1.5% to monetary or non-health benefits.

Step 2: Compute (silent)

Run the computations internally. Do not narrate; show results in the output. When BACKEND=greenbook, prefer the bridge over inline math — call econstack-greenbook with action appraise (or specific action for sub-computations) and read NPV / BCR / OB-adjusted streams / METB / discount factors back from JSON.

2.1 Real-terms rebasing (uk-gb only)

If any cash input is in a price base year other than --price-base:

rebased_value = gb_rebase(value, from = source_year, to = price_base_year)
# bridge:
echo '{"action":"appraise", ..., "base_year": <price_base>}' | econstack-greenbook

Greenbook bundles HMT's December-2025 GDP deflator. Outputs cite the deflator vintage in the KEY NUMBERS block. For non-uk-gb frameworks, the user supplies values already in the chosen base year.

2.2 Discount factors

When BACKEND=greenbook (uk-gb): factors come back from the appraise action; for ad-hoc factor lookup use action discount_factor. Greenbook schedules: standard (default), health (1.5% baseline; apply only to QALY/WELLBY rows), catastrophic (3.0%).

When BACKEND=skill (uk-gb), compute cumulatively across the kinked bands:

df(0) = 1.0
For t = 1 to horizon:
  r = STPR(t):  3.5% (1-30), 3.0% (31-75), 2.5% (76-125), 2.0% (126-200), 1.5% (201-300)
  df(t) = df(t-1) / (1 + r)

CRITICAL: cumulative compounding only. Never apply the lower rate from year 0.

For eu-brg, wb, adb, au-vic (flat rate): df(t) = 1 / (1 + r)^t.

2.3 Capital cost phasing (S-curve)

construction_years > 1: apply S-curve weights
  5-year: [0.10, 0.20, 0.30, 0.25, 0.15]
  3-year: [0.20, 0.50, 0.30]
construction_years == 1: all capex in year 0.

2.4 Optimism bias with mitigation (uk-gb)

Lookup the project category and apply the percentage from the Mott MacDonald 2002 table (greenbook: gb_optimism_bias() then gb_apply_ob(..., mitigation = ...)). Mitigation reduces the uplift proportionally:

ob_effective = ob_raw * (1 - mitigation)
adjusted_capex = capex * (1 + ob_effective)

Default mitigation = 0. Set --ob-mitigation 0.3 to 0.5 once an active risk register is in place. Typical raw uplifts: 24-44% at SOC stage, 12-24% at OBC, 3-10% at FBC. No optimism bias on opex unless the user explicitly states a duration uplift.

For eu-brg, wb, adb: skip OB; rely on scenario sensitivity. For au-vic: use Vic DTF ILG P50/P90 in place of OB.

2.5 METB (Marginal Excess Tax Burden) — uk-gb mandatory

For tax-financed costs (any cost line where the sponsor is government or where the longlist tag indicates public funding), apply 20% METB after optimism bias. Greenbook: gb_metb(rate = 0.20). Bridge action: metb.

costs_with_metb = costs_after_ob * (1 + 0.20)

This is mandatory under Green Book 2022 §5.36. Skip METB only when sponsor is private or philanthropic (no distortion from raising the funds). Show as a dedicated row in Table 2 (Costs).

2.6 Wellbeing valuation (WELLBY / QALY / VPF)

When a benefit row's quantification method is one of wellby, qaly, or vpf, route the monetisation through the dedicated greenbook function rather than generic prices. These rows are also discounted on the health schedule (1.5%) when --schedule is not overridden.

WELLBY:  echo '{"action":"wellby","life_satisfaction_change":0.5,"persons":1000,"years":3}' | bridge
QALY:    echo '{"action":"qaly","qalys":120,"scenario":"dhsc","base_year":2024}' | bridge
VPF:     echo '{"action":"vpf","year":2026,"series":"central"}' | bridge

Vintage and base year flow through to the KEY NUMBERS block.

2.7 Benefit ramp-up

linear ramp over N years:
  benefit(i) = full_annual_benefit * (i / N) for i = 1..N
post-ramp:
  benefit(i > N) = full_annual_benefit * (1 + growth_rate)^(i - N)

Default ramp: 3 years for infrastructure, 1 year for programmes. growth_rate defaults to 0; override only for programmes with documented per-capita growth (e.g. transport demand).

2.8 Carbon valuation (DESNZ Nov-2023 single consolidated series)

For uk-gb, use the consolidated central series (DESNZ Nov-2023 collapsed the historical traded / non-traded split). Override with --carbon-scenario {low|central|high}. Bridge action: carbon_npv.

phases: 'embodied' (construction years, always a cost) and 'operational' (in-use)
For each year t:
  carbon_value(t) = tCO2e(t) * carbon_price(t, scenario)
NOT adjusted for additionality (global externality).

For other frameworks: EU ETS + EC shadow (eu-brg); WB shadow USD 40-80 rising to 50-100 by 2030 (wb); ADB USD 36.30+ (adb); Australian shadow carbon (au-vic).

2.9 Do Nothing baseline

If the counterfactual has costs (deterioration, emergency repairs, rising congestion), compute their PV. For intervention options:

NPV = PV_benefits + PV_avoided_do_nothing_costs - PV_intervention_costs

Avoided counterfactual costs count as benefits of the intervention.

2.10 Additionality

Apply to all monetised benefits except: carbon (global externality), WELLBY/QALY/VPF (already net of relevant counterfactuals when computed correctly), tax-revenue items (excluded as transfers in social CBA).

adjusted_benefit = gross_benefit * (1 - deadweight) * (1 - displacement) * (1 - leakage)

2.11 Present values and economic-case metrics

PV_costs    = sum over t of [adjusted_cost(t)    * df(t)]
PV_benefits = sum over t of [adjusted_benefit(t) * df(t)]
Economic_NPV = PV_benefits - PV_costs
Economic_BCR = PV_benefits / PV_costs

VfM category (uk-gb only):
  BCR < 1.0  -> Poor
  1.0 - 1.5  -> Low
  1.5 - 2.0  -> Medium
  2.0 - 4.0  -> High
  > 4.0      -> Very High

2.12 Distributional weighting (--distributional)

When set, weight cashflows by stakeholder income relative to median equivalised income, eta = 1.3 (Green Book Annex A4 iso-elastic). Bridge action: dist_weighted_npv. Add Table 8 (Distributionally weighted NPV by stakeholder group) to the output.

echo '{"action":"dist_weighted_npv","cashflow":[...],"recipient_income":[...],"eta":1.3}' | bridge

2.13 Cost-effectiveness fallback (--cea)

If the dominant benefit is flagged as low-monetisability on the longlist (or --cea is set), skip BCR and report cost per output unit. Greenbook: gb_cost_per_unit(). The economic NPV is still computed; only the BCR row is suppressed and replaced with cost per [unit].

Step 3: Financial case (silent)

If the longlist has Cash flow tags (cash_in / cash_out / non_cash), compute the financial case using only the cash items. Non-cash items (heat mortality avoided, WELLBYs, biodiversity, air quality, carbon unless credits are sold) are excluded entirely.

If the project was entered interactively without cash tags, auto-tag:

• Capital costs → cash_out
• Operating costs → cash_out
• User fees, tariffs, grants → cash_in
• Avoided municipal or sponsor expenditure → cash_in
• Everything else → non_cash

Financial discount rate by sponsor type (flat, not declining):

• government: 4.5% real
• private: 10% real (ask for hurdle rate if stated)
• blended: weighted average of sources by capex share
• philanthropic: 0% (grants, not repayable)

Financial computations:

For each year t:
  Cash_inflow(t) = sum of cash_in items in year t
  Cash_outflow(t) = sum of cash_out items in year t
  Net_cash_flow(t) = Cash_inflow(t) - Cash_outflow(t)
  Cumulative_cash_flow(t) = Cumulative_cash_flow(t-1) + Net_cash_flow(t)

Financial_NPV = sum over t of [Net_cash_flow(t) / (1 + r_financial)^t]

Total_funding_requirement = max over t of [-Cumulative_cash_flow(t)]
  (the peak financing need: how much money the sponsor must commit before any net inflow)

Payback_period = smallest t such that Cumulative_cash_flow(t) >= 0
  (if never, report "Does not pay back within appraisal period")

Financial_IRR = the r_financial value that makes Financial_NPV = 0
  (compute numerically; report "Undefined" if no real positive root)

DSCR (only if project involves debt): if the user or longlist specifies debt parameters, compute DSCR per year of the debt term:

For each year t in the debt term:
  Operating_cash_flow_for_debt(t) = Cash_inflow(t) - (Cash_outflow(t) excluding capex and debt service)
  Debt_service(t) = scheduled interest + scheduled principal per repayment profile
  DSCR(t) = Operating_cash_flow_for_debt(t) / Debt_service(t)

Minimum_DSCR = min over debt term
Average_DSCR = mean over debt term

Flag if minimum DSCR < 1.2: "Minimum DSCR of [val] is below the typical 1.2x lender covenant. The project cannot support this debt structure. Reduce gearing, extend tenor, or find non-debt funding."

Step 4: Headline verdict (silent)

economic_sign  = "positive" if Economic_NPV > 0 else "negative"
financial_sign = "positive" if Financial_NPV > 0 else "negative"

If economic positive AND financial positive:
  "Both cases positive. Project is socially worthwhile AND financially self-sustaining. Viable for commercial or blended funding."
If economic positive AND financial negative:
  "Economic case positive, financial case negative. Project is socially worthwhile but requires public subsidy, grant, or philanthropic backing. Not viable for commercial debt on standalone cash flows."
If economic negative AND financial positive:
  "Economic case negative, financial case positive. Project generates cash for the sponsor but destroys social value (often through displacement or unpriced external costs). Reconsider before proceeding."
If economic negative AND financial negative:
  "Both cases negative. Do not proceed on these numbers."

Step 5: Sensitivity (silent)

Run four tests and summarise in one paragraph:

1. Scenario sensitivity: Pessimistic (benefits -20%, costs +20%), Central, Optimistic (benefits +20%, costs -20%). Compute NPV and BCR for each.
2. Switching values: For the top 2-3 variables, the percentage change that makes NPV = 0. Interpret correctly based on NPV sign.
3. Tornado test: For the top 5 variables by PV magnitude, ±20% shifts holding other variables central. Report the widest-range variable.
4. Discount rate sensitivity: Test the central framework rate plus one higher and one lower rate.

Report all four in one paragraph. No multi-table sensitivity section.

EANC for unequal-life options: if the options have different appraisal periods (e.g. 30-year vs 60-year), compute the equivalent annual net cost via greenbook gb_eanc() (bridge action: eanc) and add an extra row to Table 4. Without EANC, NPVs across options of unequal life are not directly comparable; flag this explicitly if EANC cannot be computed (e.g. BACKEND=skill).

echo '{"action":"eanc","npv":42.5,"years":60,"schedule":"standard"}' | bridge

Step 6: Referent group identity check (silent, uk-gb and au-vic)

For uk-gb and au-vic projects with a clear referent group, compute:

Efficiency_NPV = PV_all_benefits - PV_all_costs
Referent_Group_NPV = PV_referent_benefits - PV_referent_costs
Non_Referent_NPV = PV_non_referent_benefits - PV_non_referent_costs

Identity: Efficiency_NPV = Referent_Group_NPV + Non_Referent_NPV

If the identity does not hold, flag a tagging error. If Efficiency NPV is positive but Referent Group NPV is negative, note prominently that value is leaking outside the referent group.

Skip for wb and adb (distributional analysis by income decile replaces referent group for those frameworks).

Step 6.5: Validation gate (silent, abort on failure)

Before writing anything to disk, run the validation gate. The goal is to catch the well-known broken-CBA patterns that gb_validate() and /econ-audit check for, but at the source so a malformed appraisal never produces a file.

When BACKEND=greenbook: pass the appraisal spec through bridge action validate.

In all backends, enforce these checks:

1. Counterfactual present: Do Nothing option must exist with a non-empty description.
2. Optimism bias applied to capex when framework is uk-gb and project is investment-type.
3. METB applied when uk-gb and sponsor is government-funded (no exception for blended).
4. No transfers in benefits: tax receipts, welfare payments, intra-government grants, pure VAT recovery flagged and removed.
5. No double counts: construction employment + capex; journey time savings + land value uplift; gross earnings + tax receipts; PV of carbon savings + carbon credits sold.
6. Carbon split: if any embodied or operational carbon is in scope, it appears as its own row (not bundled into capex).
7. Cash flow tags: every line has exactly one of cash_in, cash_out, non_cash.
8. Real-terms basis: all cash inputs share the same --price-base year after rebasing.
9. Schedule alignment: health schedule applied only to QALY/WELLBY rows; not to the project as a whole.

If any check fails, do not write the file. Instead, print:

STATUS: BLOCKED | validation_gate_failed
Issue: [short description]
Fix: [pointer to the longlist field or skill flag that needs to change]

Do not fall back to a "best-effort" output. A broken CBA is worse than no CBA.

Step 7: Write the output

Save cba-[slug]-[YYYY-MM-DD].md with this exact structure.

<!-- KEY NUMBERS
framework: [framework]
sponsor: [sponsor]
project: [project name]
preferred_option: [name]
economic_npv_m: [val]
economic_bcr: [val]
economic_eanc_m: [val or n/a]
vfm_category: [category or n/a]
pv_costs_m: [val]
pv_benefits_m: [val]
financial_npv_m: [val]
financial_discount_rate: [val]
total_funding_requirement_m: [val]
payback_years: [val or "does not pay back"]
financial_irr_pct: [val or "undefined"]
min_dscr: [val or "n/a"]
optimism_bias_pct: [val]
ob_mitigation_pct: [val]
metb_applied: [yes|no]
metb_rate_pct: [val or n/a]
additionality_factor: [val]
distributional_eta: [val or n/a]
discount_schedule: [standard|health|catastrophic]
discount_rate_baseline_pct: [val]
appraisal_period: [val]
price_base_year: [val]
carbon_scenario: [low|central|high]
backend: [greenbook|skill]
greenbook_version: [val or n/a]
stpr_vintage: [val or n/a]
deflator_vintage: [val or n/a]
optimism_bias_vintage: [val or n/a]
metb_vintage: [val or n/a]
carbon_values_vintage: [val or n/a]
vpf_vintage: [val or n/a]
qaly_vintage: [val or n/a]
wellby_vintage: [val or n/a]
date: [YYYY-MM-DD]
-->

# Cost-Benefit Analysis: [Project name]

**Framework**: [framework] · **Sponsor**: [sponsor] · **Stage**: [stage] · **Date**: [YYYY-MM-DD]

## Headline

**Economic NPV**: [currency][val]m (at [social discount rate]% [declining|flat])
**Financial NPV**: [currency][val]m (at [financial discount rate]% flat)
**Verdict**: **[one-line verdict from Step 4]**

| | Economic case | Financial case |
|---|---|---|
| NPV | [val] | [val] |
| BCR / IRR | [BCR] | [IRR]% |
| Discount rate | [social] | [financial] |
| Includes | All items | Cash in and Cash out only |
| Interpretation | Societal welfare | Sponsor cash position |

## Options

Table 1: Options considered.

| # | Option | Description |
|---|--------|------------|
| 1 | Do Nothing | [Counterfactual: what happens without intervention] |
| 2 | [Do Minimum] | [description] |
| 3 | [Preferred] | [description] |

The counterfactual is dynamic: it projects forward what happens without intervention, including existing trends and committed policies.

## Costs

Table 2: Cost streams ([currency] [price base] prices, discounted at [rate]).

| Cost category | Cash flow | Undiscounted ([currency]m) | OB raw / mitigated | METB | Adjusted ([currency]m) | PV ([currency]m) |
|--------------|:---------:|---------------------------:|-------------------:|-----:|----------------------:|------------------:|
| Capital | Cash out | [val] | [X]% / [Y]% effective | +20% | [val] | [val] |
| Operating | Cash out | [val] | 0% | +20% | [val] | [val] |
| [Other] | [tag] | [val] | [val]% | [+20% or n/a] | [val] | [val] |
| **Total** | | **[val]** | | | **[val]** | **[val]** |

The METB column is `+20%` for tax-financed (government / blended) costs and `n/a` for private / philanthropic sponsors. Set to `n/a` for non-uk-gb frameworks.

## Benefits

Table 3: Benefit streams ([currency] [price base] prices).

| Benefit category | Cash flow | Undiscounted ([currency]m) | Additionality | Adjusted ([currency]m) | PV ([currency]m) |
|-----------------|:---------:|--------------------------:|--------------:|----------------------:|------------------:|
| [Category 1] | [tag] | [val] | [X]% | [val] | [val] |
| [Category 2] | [tag] | [val] | [X]% | [val] | [val] |
| [Carbon, if applicable] | Non-cash | [val] | 100% | [val] | [val] |
| **Total monetised** | | **[val]** | | **[val]** | **[val]** |

**Non-monetised benefits** (listed qualitatively, not in the BCR):
- [Benefit with direction and estimated magnitude]

## Economic case

Table 4: Economic NPV and BCR comparison.

| Metric | Do Nothing | [Option 2] | [Option 3] |
|--------|-----------:|-----------:|-----------:|
| PV Costs ([currency]m) | 0 | [val] | [val] |
| PV Benefits ([currency]m) | 0 | [val] | [val] |
| **Economic NPV ([currency]m)** | **0** | **[val]** | **[val]** |
| **BCR** | - | **[val]** | **[val]** |
| **VfM category** | - | **[category]** | **[category]** |

[Preferred option] has an economic NPV of [currency][val]m and a BCR of [val], representing [category] value for money.

## Financial case

Only Cash in and Cash out items counted. Non-cash social benefits excluded entirely.

Table 5: Cash flow profile ([currency]m).

| Year | Cash in | Cash out | Net cash flow | Cumulative |
|------|--------:|---------:|--------------:|-----------:|
| 1 | [val] | [val] | [val] | [val] |
| 2 | [val] | [val] | [val] | [val] |
| ... | ... | ... | ... | ... |

Table 6: Financial metrics.

| Metric | Value |
|--------|------:|
| Total funding requirement (peak financing need) | [currency][val]m |
| Financial NPV | [currency][val]m |
| Financial IRR | [val]% or "Undefined" |
| Payback period | [val] years or "does not pay back" |
| Minimum DSCR (if debt) | [val] or "n/a" |

**Interpretation**: [one paragraph drawn from the verdict block, explaining the economic-vs-financial split and what it means for funding strategy]

## Sensitivity

[One paragraph covering all four sensitivity tests. Example shape: "The Economic NPV is robust under pessimistic scenario (NPV [val], BCR [val]) and remains positive at discount rates up to [X]%. The top sensitivity is [variable] (widest tornado range, [val]m span). Benefits could fall by [X]% before the NPV turns negative. The Financial NPV is [structurally negative / positive under all scenarios] and [is / is not] rescued by any plausible parameter change."]

## Stakeholder (if uk-gb or au-vic)

Table 7: Multiple account view.

| Stakeholder group | In referent group? | PV costs ([currency]m) | PV benefits ([currency]m) | Net position |
|-------------------|:-----------------:|----------------------:|--------------------------:|-------------:|
| [Local residents] | Yes | [val] | [val] | [val] |
| [Municipality] | Yes | [val] | [val] | [val] |
| [Foreign contractors] | No | [val] | [val] | [val] |
| **Referent group total** | | **[val]** | **[val]** | **[val]** |
| **Efficiency total** | | **[val]** | **[val]** | **[val]** |

Identity check: Referent Group NPV + Non-Referent NPV = Efficiency NPV. [Any deviation is a tagging error.]

## Recommendation

[One paragraph: preferred option, key conditions for proceeding (e.g. "subject to securing PNRR grant of EUR 40m"), and flags on the biggest risks from the sensitivity paragraph.]

## Next step

- `/business-case` to wrap this in the Five Case Model for a spending bid (when revived).
- `/econ-audit` to check for residual CBA errors.

That is the full default deliverable.

Step 7.5: Sidecar JSON

Alongside the markdown, write a structured cba-[slug]-[YYYY-MM-DD].json file containing the full appraisal object: every input (costs, benefits, years, framework, sponsor, schedule, base year), every parameter (OB, OB mitigation, METB, additionality, distributional eta, carbon scenario), every output (NPV, BCR, EANC, PV, optimism_bias_pct, METB applied, costs_adjusted, benefits_adjusted), and the full data_versions array from the bridge. Schema version 1.

The JSON is the structured handoff that /business-case (when revived) will consume as the Economic Case of the Five Case Model.

Step 8: Auto-audit hook (default on)

After Steps 7 and 7.5 complete, invoke the econ-audit skill against the produced markdown unless --no-audit is set.

Skill(econ-audit) with input: cba-[slug]-[date].md

Capture the audit's RAG counts and append to the closing message (single line: Audit: 0 RED, 1 AMBER). Do not paste the full audit into the chat. The user can re-run /econ-audit cba-[slug]-[date].md for the full report.

If RED count > 0, change the closing status from DONE to DONE_WITH_CONCERNS and include the first RED issue's headline.

Sub-component selection (via --section): emit only the requested parts. Always include the KEY NUMBERS comment and header block.

• full (default): the whole structure above.
• headline: header + headline block only.
• costs: header + costs table only.
• benefits: header + benefits table only.
• economic: header + economic case only.
• financial: header + financial case only.
• sensitivity: header + sensitivity paragraph only.
• stakeholder: header + stakeholder table only.
• Combinable: --section headline,financial,sensitivity.

Format exports (multi-format via --format):

• Markdown (.md): always generated. cba-[slug]-[date].md.
• Excel (.xlsx) (if xlsx in --format): invoke the xlsx skill. Workbook with sheets: Summary (headline and key numbers), Costs, Benefits, Cash flow (year-by-year), Sensitivity, Stakeholder. Blue input cells for key assumptions so the user can re-run scenarios. Save as cba-[slug]-[date].xlsx.
• Word (.docx) (if word in --format): invoke the docx skill. One document, the full structure with cover page and hyperlinked references. Save as cba-[slug]-[date].docx.
• PowerPoint (.pptx) (if pptx in --format): invoke the pptx skill. 8 slides: (1) Problem and options, (2) Headline verdict, (3) Costs, (4) Benefits, (5) Economic NPV, (6) Financial case, (7) Sensitivity, (8) Recommendation. Action titles. Save as cba-[slug]-[date].pptx.
• PDF (if pdf in --format): render markdown through econstack Quarto template. Save as cba-[slug]-[date].pdf.
• all: expand to all five formats.

Tell the user (listing only files actually produced):

CBA complete. [Preferred option] NPV [val], BCR [val], VfM [category]. METB applied: [yes|no]. Backend: [greenbook|skill]. Audit: [N] RED, [N] AMBER.

Saved:
  cba-[slug]-[date].md
  cba-[slug]-[date].json
  [other formats if requested]

Next: /econ-audit cba-[slug]-[date].md for the full audit report.

If --no-audit was set, omit the Audit: field from the headline. If BACKEND=skill, append a one-line note recommending install.packages('greenbook') for full reproducibility and vintage stamping.

Framework-specific rules

uk-gb (UK HMT Green Book)

• Kinked STPR: 3.5% years 0-30, 3.0% 31-75, 2.5% 76-125, 2.0% 126-200, 1.5% 201-300 (greenbook gb_stpr()).
• Optimism bias mandatory on capital costs per HMT supplementary Table 1 (Mott MacDonald 2002) by project type and stage. Mitigation factor 0 unless --ob-mitigation is set; typical 30-50% reduction once an active risk register is in place.
• METB of 20% on all tax-financed costs (mandatory per Green Book 2022 §5.36). Skip only when sponsor is private or philanthropic.
• Real-terms rebasing via the bundled HMT December-2025 GDP deflator. Set price base via --price-base.
• Additionality: standard 20% deadweight, 25% displacement, 10% leakage unless user overrides.
• Health outcomes use the health schedule (1.5% baseline) on QALY/WELLBY rows only. Monetary benefits stay on standard (3.5%).
• WELLBY (HMT Wellbeing Guidance July 2021), QALY (DHSC supplementary), VPF (DfT TAG v2.03FC) all sourced from greenbook with vintage metadata.
• Carbon: DESNZ Nov-2023 single consolidated series (low / central / high); historical traded vs non-traded split has been retired.
• Referent group analysis mandatory if stakeholder groups cross the national boundary.
• Distributional weights (Annex A4 iso-elastic, eta = 1.3, reference = median equivalised income) under --distributional.

eu-brg (EU Better Regulation)

• Flat 3% (advanced Member States) or 5% (convergence MS) discount rate.
• No optimism bias; use scenario sensitivity.
• SME test mandatory for regulations affecting business.
• Fundamental rights impact must be screened.
• EU ETS price for carbon, EEA NEEDS for air quality damage costs.

wb (World Bank)

• Country-specific ERR (typically 6%).
• Distributional incidence mandatory: report NPV by income decile and poverty headcount impact.
• WB shadow carbon price (USD 40-80/tCO2, rising to USD 50-100 by 2030).
• Shadow wages for labour (typically 30-50% of market wage for non-working time in low-income contexts).
• No optimism bias; use scenario sensitivity.

adb (ADB)

• 9% EIRR hurdle (6% for climate, health, education per 2017 revision).
• Switching values mandatory on all major variables.
• Poverty and gender disaggregation mandatory.
• ADB shadow carbon price (USD 36.30+/tCO2).
• Local shadow wages by country and skill level.
• No optimism bias.

au-vic (Victorian HVHR)

• 4% for infrastructure, 7% for non-infrastructure (flat).
• Vic DTF ILG risk allowance replaces optimism bias; typically P50 and P90 estimates.
• Benefit Management Plan structure: every benefit must have owner, KPI, baseline, target, realisation timeframe.
• ATAP M1 for transport sub-cases; ATAP PV5 for unit values.
• Referent group typically Victorian residents; all-Australian for interstate benefits.

Important rules

• Counterfactual is mandatory. Every benefit and cost is incremental to Do Nothing. The counterfactual must be dynamic, not a static snapshot of today.
• One interactive moment. Step 1 collects project, options, costs, benefits in one batch. No other AskUserQuestion calls unless a longlist file is malformed.
• Silent working. Do not narrate the discount computation, optimism bias lookup, METB, real-terms rebasing, or sensitivity logic. Show the result.
• METB is mandatory under Green Book 2022 §5.36 for tax-financed costs (uk-gb, sponsor government or blended). 20% rate. Skip only when sponsor is private or philanthropic.
• Optimism bias mitigation never zero by handwaving. If the user claims mitigation > 0, the validation gate requires a corresponding risks block on the longlist or --risks. Otherwise reset to 0.
• Carbon is not adjusted for additionality (global externality). Always split into embodied (construction) and operational (in-use). DESNZ Nov-2023 retired the traded / non-traded distinction; use a single consolidated series per scenario.
• Transfers are excluded from social CBA. Tax receipts, welfare payments, grant receipts between government bodies are not net social benefits. METB sits above this rule: it is a real distortion on the funds raised, not a transfer.
• Sunk costs are excluded. Resources already committed that cannot be recovered are irrelevant to the forward-looking decision.
• **Cash flow tags drive the financial case.

…(truncated)