# Policyengine Parameter Patterns

> PolicyEngine parameter patterns - YAML structure, naming conventions, metadata requirements, federal/state separation

- Skill: `majiayu000/policyengine-parameter-patterns-2` (Agent Skill, multi-file: 2 files)
- Install (CLI): `npx skillmds@latest add majiayu000/policyengine-parameter-patterns-2`
- Raw SKILL.md: https://api.skillmd.com/api/skills/majiayu000/policyengine-parameter-patterns-2/raw
- Safety review: pending (external: skill-scanner WARNING, skillspector CAUTION)
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Coding & Dev Tools
- Author: majiayu000 (https://skillmd.com/u/majiayu000)
- Updated: 2026-09-22
- Page: https://skillmd.com/skills/majiayu000/policyengine-parameter-patterns-2

---


# PolicyEngine Parameter Patterns

Comprehensive patterns for creating PolicyEngine parameter files.

## Critical: Required Structure

Every parameter MUST have this exact structure:
```yaml
description: [One sentence description].
values:
  YYYY-MM-DD: value

metadata:
  unit: [type]       # REQUIRED
  period: [period]   # REQUIRED
  label: [name]      # REQUIRED
  reference:         # REQUIRED
    - title: [source]
      href: [url]
```

**Missing ANY metadata field = validation error**

---

## 1. File Naming Conventions

### Study Reference Implementations First
Before naming, examine:
- DC TANF: `/parameters/gov/states/dc/dhs/tanf/`
- IL TANF: `/parameters/gov/states/il/dhs/tanf/`
- TX TANF: `/parameters/gov/states/tx/hhs/tanf/`

### Naming Patterns

**Dollar amounts → `/amount.yaml`**
```
income/deductions/work_expense/amount.yaml     # $120
resources/limit/amount.yaml                    # $6,000
payment_standard/amount.yaml                   # $320
```

**Percentages/rates → `/rate.yaml` or `/percentage.yaml`**
```
income_limit/rate.yaml                         # 1.85 (185% FPL)
benefit_reduction/rate.yaml                    # 0.2 (20%)
income/disregard/percentage.yaml               # 0.67 (67%)
```

**Thresholds → `/threshold.yaml`**
```
age_threshold/minor_child.yaml                 # 18
age_threshold/elderly.yaml                     # 60
income/threshold.yaml                          # 30_000
```

---

## 2. Description Field

### The ONLY Acceptable Formula

```yaml
description: [State] [verb] [category] to [this X] under the [Full Program Name] program.
```

**Components:**
1. **[State]**: Full state name (Indiana, Texas, California)
2. **[verb]**: ONLY use: limits, provides, sets, excludes, deducts, uses
3. **[category]**: What's being limited/provided (gross income, resources, payment standard)
4. **[this X]**: ALWAYS use generic placeholder
   - `this amount` (for currency-USD)
   - `this share` or `this percentage` (for rates/percentages)
   - `this threshold` (for age/counts)
5. **[Full Program Name]**: ALWAYS spell out (Temporary Assistance for Needy Families, NOT TANF)

### Copy These Exact Templates

**For income limits:**
```yaml
description: [State] limits gross income to this amount under the Temporary Assistance for Needy Families program.
```

**For resource limits:**
```yaml
description: [State] limits resources to this amount under the Temporary Assistance for Needy Families program.
```

**For payment standards:**
```yaml
description: [State] provides this amount as the payment standard under the Temporary Assistance for Needy Families program.
```

**For disregards:**
```yaml
description: [State] excludes this share of earnings from countable income under the Temporary Assistance for Needy Families program.
```

### Description Validation Checklist

Run this check on EVERY description:
```python
# Pseudo-code validation
def validate_description(desc):
    checks = [
        desc.count('.') == 1,  # Exactly one sentence
        'TANF' not in desc,     # No acronyms
        'SNAP' not in desc,     # No acronyms
        'this amount' in desc or 'this share' in desc or 'this percentage' in desc,
        'under the' in desc and 'program' in desc,
        'by household size' not in desc,  # No explanatory text
        'based on' not in desc,           # No explanatory text
        'for eligibility' not in desc,    # Redundant
    ]
    return all(checks)
```

**CRITICAL: Always spell out full program names in descriptions!**

---

## 3. Values Section

### Format Rules
```yaml
values:
  2024-01-01: 3_000    # Use underscores
  # NOT: 3000

  2024-01-01: 0.2      # Remove trailing zeros
  # NOT: 0.20 or 0.200

  2024-01-01: 2        # No decimals for integers
  # NOT: 2.0 or 2.00
```

### Effective Dates

**Use exact dates from sources:**
```yaml
# If source says "effective July 1, 2023"
2023-07-01: value

# If source says "as of October 1"
2024-10-01: value

# NOT arbitrary dates:
2000-01-01: value  # Shows no research
```

**Date format:** `YYYY-MM-01` (always use 01 for day)

---

## 4. Metadata Fields (ALL REQUIRED)

### unit
Common units:
- `currency-USD` - Dollar amounts
- `/1` - Rates, percentages (as decimals)
- `month` - Number of months
- `year` - Age in years
- `bool` - True/false
- `person` - Count of people

### period
- `year` - Annual values
- `month` - Monthly values
- `day` - Daily values
- `eternity` - Never changes

### label
Pattern: `[State] [PROGRAM] [description]`
```yaml
label: Montana TANF minor child age threshold
label: Illinois TANF earned income disregard rate
label: California SNAP resource limit
```
**Rules:**
- Spell out state name
- Abbreviate program (TANF, SNAP)
- No period at end

### reference
**Requirements:**
1. At least one source (prefer two)
2. Must contain the actual value
3. **Title: Include FULL section path** (all subsections and sub-subsections)
4. **PDF links: Add `#page=XX` at end of href ONLY** (never in title)

**Title Format - Include ALL subsection levels (NO page numbers):**
```yaml
# ❌ BAD - Too generic:
title: OAR 461-155  # Missing subsections!
title: Section 5    # Which subsection?
title: TEA Manual, page 13  # Page number belongs in href, not title!

# ✅ GOOD - Full section path, no page number:
title: OAR 461-155-0030(2)(a)(B)     # All levels included
title: 7 CFR § 273.9(d)(6)(ii)(A)    # Federal regulation with all subsections
title: Indiana Admin Code 12-14-2-3.5(b)(1)  # State admin code
title: Arkansas TEA Manual Section 5.2.3    # Manual with section (page in href)
```

**PDF Link Format - Always include page in href:**

**CRITICAL: Use the PDF file page number, NOT the printed page number inside the document.**
- The `#page=XX` value is the page position in the PDF file (1st page = 1, 2nd page = 2, etc.)
- This may differ from the page number printed on the document itself
- **Why?** When users click the link, they must land directly on the page showing the referenced values

```yaml
# ❌ BAD - No page number:
href: https://state.gov/manual.pdf

# ✅ GOOD - Page anchor in href (file page number):
href: https://humanservices.arkansas.gov/wp-content/uploads/TEA_MANUAL.pdf#page=13
href: https://adminrules.idaho.gov/rules/current/16/160503.pdf#page=8
```

**Complete Examples:**
```yaml
✅ GOOD (page number in href only):
reference:
  - title: OAR 461-155-0030(2)(a)(B)
    href: https://oregon.public.law/rules/oar_461-155-0030
  - title: Oregon DHS TANF Policy Manual Section 4.3.2
    href: https://oregon.gov/dhs/tanf-manual.pdf#page=23

✅ GOOD:
reference:
  - title: 7 CFR § 273.9(d)(6)(ii)(A)
    href: https://www.ecfr.gov/current/title-7/section-273.9#p-273.9(d)(6)(ii)(A)
  - title: Arkansas TEA Manual Section 2100
    href: https://humanservices.arkansas.gov/wp-content/uploads/TEA_MANUAL.pdf#page=45

❌ BAD (page number in title):
reference:
  - title: Arkansas TEA Manual, page 13  # Page belongs in href!
    href: https://humanservices.arkansas.gov/wp-content/uploads/TEA_MANUAL.pdf

❌ BAD (missing info):
reference:
  - title: Federal LIHEAP regulations  # Too generic - no section!
    href: https://www.acf.hhs.gov/ocs  # No specific page
  - title: OAR 461-155  # Missing subsections (2)(a)(B)!
    href: https://oregon.gov/manual.pdf  # Missing #page=XX
```

---

## 5. Federal/State Separation

### Federal Parameters
Location: `/parameters/gov/{agency}/{program}/`
```yaml
# parameters/gov/hhs/fpg/first_person.yaml
description: HHS sets this amount as the federal poverty guideline for one person.
```

### State Parameters
Location: `/parameters/gov/states/{state}/{agency}/{program}/`
```yaml
# parameters/gov/states/ca/dss/tanf/income_limit/rate.yaml
description: California uses this multiplier of the federal poverty guideline for TANF income eligibility.
```

---

## 5.5 Parameter Folder Organization

### Core Principles

1. **Group logically** - Parameters that relate to the same aspect should be together
2. **Don't create subfolder for 1 file** - If only 1 parameter for an aspect, keep it at parent level
3. **Payment standard at root** - Main benefit amounts can stay at program root

### Common Aspects (adapt to your program)

- `income/` - Income limits, deductions, disregards
- `eligibility/` - Age thresholds, citizenship requirements
- `resources/` - Asset/resource limits

### Study Existing Implementations

Each program is different. Before organizing, look at similar programs:
```bash
ls policyengine_us/parameters/gov/states/{state}/{agency}/
```

---

## 6. Common Parameter Patterns

### Income Limits (as FPL multiplier)
```yaml
# income_limit/rate.yaml
description: State uses this multiplier of the federal poverty guideline for program income limits.
values:
  2024-01-01: 1.85  # 185% FPL

metadata:
  unit: /1
  period: year
  label: State PROGRAM income limit multiplier
```

### Benefit Amounts
```yaml
# payment_standard/amount.yaml
description: State provides this amount as the monthly program benefit.
values:
  2024-01-01: 500

metadata:
  unit: currency-USD
  period: month
  label: State PROGRAM payment standard amount
```

### Age Thresholds (Simple)
```yaml
# age_threshold/minor_child.yaml
description: State defines minor children as under this age for program eligibility.
values:
  2024-01-01: 18

metadata:
  unit: year
  period: eternity
  label: State PROGRAM minor child age threshold
```

### Age-Based Eligibility (Bracket Style) - PREFERRED

**When eligibility depends on age ranges, use a single bracket-style parameter instead of separate min/max files.**

```yaml
# eligibility/by_age.yaml
description: Massachusetts determines eligibility for the Bay Transportation reduced fare program based on age.

metadata:
  threshold_unit: year
  amount_unit: bool
  period: year
  type: single_amount
  label: Massachusetts Bay Transportation reduced fare age eligibility
  reference:
    - title: MBTA Reduced Fare Program
      href: https://www.mbta.com/fares/reduced

brackets:
  - threshold:
      2024-01-01: 0
    amount:
      2024-01-01: false    # Under 18: not eligible
  - threshold:
      2024-01-01: 18
    amount:
      2024-01-01: true     # Ages 18-64: eligible
  - threshold:
      2024-01-01: 65
    amount:
      2024-01-01: false    # 65+: not eligible (different program)
```

**Federal example (SNAP student eligibility):**
```yaml
# parameters/gov/usda/snap/student_age_eligibility_threshold.yaml
description: The United States includes students in this age range for SNAP eligibility.

brackets:
  - threshold:
      2018-01-01: 0
    amount:
      2018-01-01: true     # Under 18: eligible
  - threshold:
      2018-01-01: 18
    amount:
      2018-01-01: false    # Ages 18-49: not eligible (student restrictions)
  - threshold:
      2018-01-01: 50
    amount:
      2018-01-01: true     # 50+: eligible

metadata:
  type: single_amount
  threshold_unit: year
  amount_unit: bool
  label: SNAP student age eligibility threshold
  reference:
    - title: 7 U.S. Code § 2015 - Eligibility disqualifications
      href: https://www.law.cornell.edu/uscode/text/7/2015
```

**When to use bracket-style:**
- ✅ Eligibility varies by age range (eligible for ages X-Y only)
- ✅ Multiple age cutoffs affect the same benefit
- ✅ Boolean eligibility that changes at different thresholds
- ✅ Non-contiguous eligibility (e.g., eligible under 18 AND over 50, but not 18-49)

**When NOT to use bracket-style:**
- ❌ Single threshold (just use simple `threshold.yaml`)
- ❌ Non-boolean values that scale with age (use `single_amount` brackets with currency amounts)

### Disregard Percentages
```yaml
# income/disregard/percentage.yaml
description: State excludes this share of earned income from program calculations.
values:
  2024-01-01: 0.67  # 67%

metadata:
  unit: /1
  period: eternity
  label: State PROGRAM earned income disregard percentage
```

### Bracket-Based Parameters

**CRITICAL: Handling Negative Values**

When creating bracket-based parameters (e.g., tax credits based on AGI), the first bracket threshold MUST be `-.inf` if negative values are possible, NOT `0`.

**❌ WRONG - Excludes negative AGI:**
```yaml
# threshold.yaml (for single filers)
brackets:
  - threshold:
      2023-01-01: 0      # ❌ Bug: negative AGI excluded!
    amount:
      2023-01-01: 300
  - threshold:
      2023-01-01: 30_000
    amount:
      2023-01-01: 110
```

**✅ CORRECT - Includes all possible values:**
```yaml
# threshold.yaml (for single filers)
brackets:
  - threshold:
      2023-01-01: -.inf  # ✅ Covers negative AGI
    amount:
      2023-01-01: 300
  - threshold:
      2023-01-01: 30_000
    amount:
      2023-01-01: 110
```

**When to use `-.inf`:**
- Income-based calculations (AGI can be negative)
- Any parameter where negative input values are valid
- Tax credits, deductions, or benefits based on earnings

**When `0` is appropriate:**
- Age thresholds (always non-negative)
- Count-based parameters (household size, number of dependents)
- Resource limits (assets can't be negative)

**Real-world example:** Hawaii Food/Excise Tax Credit uses AGI brackets. The first threshold must be `-.inf` to correctly handle taxpayers with negative AGI (e.g., business losses).

---

## 7. Validation Checklist

Before creating parameters:
- [ ] Studied reference implementations (DC, IL, TX)
- [ ] All four metadata fields present
- [ ] Description is one complete sentence
- [ ] Values use underscore separators
- [ ] Trailing zeros removed from decimals
- [ ] References include subsections and page numbers
- [ ] Label follows naming pattern
- [ ] Effective date matches source document

---

## 8. Common Mistakes to Avoid

### Missing Metadata
```yaml
❌ WRONG - Missing required fields:
metadata:
  unit: currency-USD
  label: Benefit amount
  # Missing: period, reference
```

### Generic References
```yaml
❌ WRONG:
reference:
  - title: State TANF Manual
    href: https://state.gov/tanf

✅ CORRECT:
reference:
  - title: State TANF Manual Section 5.2, page 15
    href: https://state.gov/tanf-manual.pdf#page=15
```

### Arbitrary Dates
```yaml
❌ WRONG:
values:
  2000-01-01: 500  # Lazy default

✅ CORRECT:
values:
  2023-07-01: 500  # From source: "effective July 1, 2023"
```

---

## Real-World Examples from Production Code

**CRITICAL: Study actual parameter files, not just examples!**

Before writing ANY parameter:
1. Open and READ 3+ similar parameter files from TX/IL/DC
2. COPY their exact description pattern
3. Replace state name and specific details only

### Payment Standards
```yaml
# Texas (actual production)
description: Texas provides this amount as the payment standard under the Temporary Assistance for Needy Families program.

# Pennsylvania (actual production)
description: Pennsylvania limits TANF benefits to households with resources at or below this amount.
```

### Income Limits
```yaml
# Indiana (should be)
description: Indiana limits gross income to this amount under the Temporary Assistance for Needy Families program.

# Texas (actual production)
description: Texas limits countable resources to this amount under the Temporary Assistance for Needy Families program.
```

### Disregards
```yaml
# Indiana (should be)
description: Indiana excludes this share of earnings from countable income under the Temporary Assistance for Needy Families program.

# Texas (actual production)
description: Texas deducts this standard work expense amount from gross earned income for Temporary Assistance for Needy Families program calculations.
```

### Pattern Analysis
- **ALWAYS** spell out full program name
- Use "under the [Program] program" or "for [Program] program calculations"
- One simple verb (limits, provides, excludes, deducts)
- One "this X" placeholder
- NO extra explanation ("based on X", "This is Y")

### Common Description Mistakes to AVOID

**❌ WRONG - Using acronyms:**
```yaml
description: Indiana sets this gross income limit for TANF eligibility by household size.
# Problems: "TANF" not spelled out, unnecessary "by household size"
```

**✅ CORRECT:**
```yaml
description: Indiana limits gross income to this amount under the Temporary Assistance for Needy Families program.
```

**❌ WRONG - Adding explanatory text:**
```yaml
description: Indiana provides this payment standard amount based on household size.
# Problem: "based on household size" is unnecessary (evident from breakdown)
```

**✅ CORRECT:**
```yaml
description: Indiana provides this amount as the payment standard under the Temporary Assistance for Needy Families program.
```

**❌ WRONG - Missing program context:**
```yaml
description: Indiana sets the gross income limit.
# Problem: No program name, no "this amount"
```

**✅ CORRECT:**
```yaml
description: Indiana limits gross income to this amount under the Temporary Assistance for Needy Families program.
```

### Authoritative Source Requirements

**ONLY use official government sources:**
- ✅ State codes and administrative regulations
- ✅ Official state agency websites (.gov domains)
- ✅ Federal regulations (CFR, USC)
- ✅ State plans and official manuals (.gov PDFs)

**NEVER use:**
- ❌ Third-party guides (singlemotherguide.com, benefits.gov descriptions)
- ❌ Wikipedia
- ❌ Nonprofit summaries (unless no official source exists)
- ❌ News articles

---

## For Agents

When creating parameters:
1. **READ ACTUAL FILES** - Study TX/IL/DC parameter files, not just skill examples
2. **Include ALL metadata fields** - missing any causes errors
3. **Use exact effective dates** from sources
4. **Follow naming conventions** (amount/rate/threshold)
5. **Write simple descriptions** with "this" placeholders and full program names
6. **Include ONLY official government references** with subsections and pages
7. **Format values properly** (underscores, no trailing zeros)