`zip_code`: a 5-digit US ZIP. A good first call to validate a ZIP before
asking for more detail. Returns the state, number of returns, number of
individuals, and the SOI tax year. ZIPs with <100 returns are excluded.

`zip_code`: a 5-digit US ZIP. Returns total adjusted gross income (AGI),
average AGI per return, and the main income components — salaries and wages,
taxable interest, ordinary dividends, business net income, and net capital
gain. All dollar amounts in USD.

Note: figures cover filed tax returns only. Average AGI is a *mean per
return*, not a median per household, and AGI omits most nontaxable income —
so it is not directly comparable to Census median household income.

`zip_code`: a 5-digit US ZIP. Returns, for each bracket (<$25k, $25-50k,
$50-75k, $75-100k, $100-200k, $200k+), the number of returns and total AGI
plus each bracket's share of the ZIP's returns and AGI. This is the income
*shape* of a ZIP — what a single median can't show.

Note: a bracket showing 0 may be IRS-suppressed (<20 returns in that cell)
rather than truly empty, so the other brackets' shares can be slightly
overstated.

`zip_code`: a 5-digit US ZIP. Returns income tax, income tax before credits,
total tax liability (broader — includes self-employment tax and other taxes),
total tax payments, and the average total tax per return. Amounts in USD.

`zip_code`: a 5-digit US ZIP. Returns the number of returns and total amount
for the Earned Income Tax Credit (overall and split by number of qualifying
children: none / one / two / three or more), plus the additional (refundable)
child tax credit. Amounts in USD.

Note: a 0 may be IRS-suppressed (<20 returns in each AGI-bracket cell)
rather than a true zero — it does not prove no one claims the credit.

`zip_code`: a 5-digit US ZIP. Returns the count and amount of standard
deductions and itemized deductions, the taxes-paid (SALT) deduction, and the
percent of returns that itemized. Amounts in USD.

Note: a 0 may be IRS-suppressed (<20 returns in each AGI-bracket cell)
rather than a true zero — it does not prove no one in the ZIP itemizes.

`zip_code`: a 5-digit US ZIP. Returns the number of single, married-filing-
jointly, and head-of-household returns, the number of elderly returns (age
65+), and the count and share of electronically filed returns.

Note: a 0 count may be IRS-suppressed (<20 returns in each AGI-bracket
cell) rather than truly absent.

`zips`: a list of 5-digit US ZIPs to compare. `metric`: one of
`total_returns`, `adjusted_gross_income`, `avg_agi_per_return`,
`pct_returns_200k_plus`, `total_income`, `salaries_and_wages`, `income_tax`,
`total_tax_liability`, `avg_total_tax_per_return`, `eitc_amount`. Returns each
ZIP's value, sorted descending; ZIPs with no SOI data are listed last. A 0
for a sparse metric (e.g. `eitc_amount`) may be IRS-suppressed, not a true
zero.

`state`: a 2-letter USPS code (e.g. 'CA') or full state name (e.g.
'California'). Returns the state's total returns, individuals, AGI, average
AGI per return, income tax, total tax liability, and the income distribution
across the six AGI brackets. Drawn from the IRS 00000 state-total row.

`zip_code`: a 5-digit US ZIP. `field`: a SOI field code (e.g. `A00100` for
AGI, `N1` for number of returns); case-insensitive. Returns that field summed
across the ZIP's AGI brackets, with its label and unit (USD for amount fields,
count for return counts). Limited to the fields held in the local store (the
same ones the other tools draw on); an unknown field errors with the list.

Note: a 0 may be IRS-suppressed (<20 returns in a cell) rather than a true
zero, and a sum over suppressed cells slightly understates the real total.