Cite the section, not the summary.

The real text of federal and state tax law, cited to the section and checked before it reaches a workpaper — for CPAs, EAs, tax attorneys and the software they use.

26 U.S.C. § 6651(a)(2)

Failure to file tax return or to pay tax

Every authority a tax position rests on

In one consistent format across five jurisdictions — typed, dated, and superseded guidance marked and dropped from search unless cited directly.

Federal
Code sections26 U.S.C., with ERISA, the Bank Secrecy Act and the Social Security Act	uscode.house.gov	2,454
Regulation sectionsTreasury regulations, with 29, 31, 17 and 20 CFR	eCFR	8,197
IRB documents^¹Revenue rulings, procedures, notices and T.D.s since 2004	IRS	6,957
IRM sectionsHow the IRS says it works a case. Procedure, not law.	IRS	29,633
Forms, instructions, publicationsTax years 2025 and 2026, cut at the IRS's own headings	IRS	7,419
Tax Court opinionsServed as issued	ustaxcourt.gov	447
California
Code, regs, rulings and decisionsRev. & Tax. Code + 8 codes, CCR 18, FTB, CDTFA, OTA, BOE	leginfo.ca.gov	19,697
Washington
Code, regs, rulings and decisionsRCW 82–84, WAC 458, Tax Decisions, Excise Tax Advisories	leg.wa.gov	11,088
New York
Code, regs, rulings and decisionsTax Law + 10 laws, 20 NYCRR, TSB-Ms/As, Tax Appeals	nysenate.gov	5,294
New York City
Code, rules and decisionsAdmin. Code Title 11, RCNY Title 19, Tax Appeals Tribunal	nyc.gov	1,458
Total		93,000+

Every record links to the government publisher it came from; tax year is a hard partition, so a 2025 question never sees a 2026 form.

Two ways to reach the corpus, one key

MCP

The same corpus inside Claude, Cursor or any MCP client. Ask in plain English; the agent cites the section with a stable ID like us/irc/6651.

claude mcp add:

claude mcp add --transport http tax-law \
  https://www.taxcitation.com/mcp \
  --header "Authorization: Bearer $KEY"

"What does IRC § 6651(a)(2) say?"
"Does Washington tax digital automated services? Cite the RCW."
"Check the citations in this memo."

search_tax_lawget_sectionsresolve_citationverify_citationsanswer_tax_question

REST

The hosted API, for products that look up tax law a section at a time — IRC, R&TC, RCW and Rev. Proc. cites all resolve to one exact provision.^¹

/v1/search · /v1/contents · /v1/resolve · /v1/verify · /v1/answer

Request:

curl "https://www.taxcitation.com/v1/resolve\
?cite=R%26TC%20%C2%A7%2019132(a)(1)" \
  -H "Authorization: Bearer $KEY"

Response:

{
  "data": {
    "citeId": "ca/rtc/19132",
    "pinpoint": "(a)(1)",
    "pinpointFound": true,
    "jurisdiction": "US-CA",
    "status": "in_force"
  },
  "meta": {
    "latencyMs": 212,
    "creditsConsumed": 2
  }
}

Usage-based credits, not seats

One credit is $0.01. Every key gets the full corpus. Try it without a key first: federal and California law, 250 lookups a day.

Call	Credits	USD
Resolve a citation	2	$0.02
Section text, per section: highlights only / full text	2 / 6	$0.02 / $0.06
Search with verbatim highlights / with passage text	4 / 8	$0.04 / $0.08
Verify a cited claim	4 per claim	$0.04 + tokens^¹
Verified answer	4 + tokens	$0.04 + tokens^¹

Pay as you go: federal, CA, WA, NY and NYC on every key, REST and MCP alike, up to 10 keys, billed monthly from Stripe — cancel any time; failed calls cost nothing.

Firm or platform? Talk to us.

What we measure

Catches wrong or unsupported citations 219 held-out test cases; each citation is resolved, the section quoted, and a classifier judges support.

99.3%

Accepts correct citations Same 219 held-out test cases.

98.6%

Claims in verified answers supported by the cited law 73 held-out questions; every citation resolved to a real section.

97.9%

Time to resolve a citation Search takes 0.2–0.8 s; a verified answer about 12 s at the median.

0.1–0.3 s

Full method, held-out cases and raw results: TaxCalcBench.

Questions

What does it cover?

Federal tax law (IRC, Treasury regulations, IRB guidance, IRM, IRS forms and publications for 2025–2026, Tax Court) and California, Washington, New York and New York City tax law. Other states are added from each state's own publisher.

How does billing work?

Each call costs credits ($0.01 each), shown as creditsConsumed on every response. Verified answers also pass through the actual token cost of drafting and checking them, plus 50%. Stripe bills monthly in arrears; the first $5 is on us.

Is this tax advice?

No. It returns the law and checks citations. A professional still signs the return.

Which models power verified answers?

GLM-5.3-Flash, an open-weight model hosted on Baseten, drafts the answer; TypeSafe's Jev checks every claim against the section it cites. The model and its cost are on every answer.