Every Feather answer cites one corpus of primary tax law: the Internal Revenue Code, Treasury regulations, IRS guidance, Tax Court opinions, and the law of every state and territory. We crawl, parse and index it ourselves.
- 01 Crawl
One crawler per source walks the Internal Revenue Code, Treasury regulations, the Federal Register, Internal Revenue Bulletins, IRS forms and publications, Tax Court opinions and state revenue sites on a recurring schedule.
- 02 Triage
Every download is checksummed. Unchanged documents are set aside and revised ones replace the version they supersede.
- 03 Extract
PDFs and web pages become clean Markdown, page by page, keeping headings, tables and page numbers.
- 04 Chunk
Each document is cut into overlapping passages sized for retrieval, each tagged with its source, jurisdiction and pages.
- 05 Store
Passages are embedded and indexed for vector and full-text search, then reranked at query time so the controlling law comes first.
As of Nov 4, 2026, 10:34 AM UTC
Always current
Tax law changes every week: revenue rulings and notices in the Internal Revenue Bulletin, final and proposed regulations in the Federal Register, new Tax Court opinions, revised forms and instructions, and guidance from state revenue departments.
Feather's crawlers revisit each source on a schedule, pick up what changed and index it automatically. A revised document replaces the version it supersedes, so search returns the text in force today.
This week's changes: the Tax Brief
2026 Form 1096Federal · IRS forms54d ago- Form 434 (8-2026)Federal · IRS forms54d ago
- Form 14157 (Rev. 8-2026)Federal · IRS forms54d ago
- Tax Rate Schedule TableFederal · Test KB83d ago
Tax Rate Schedule TableCalifornia · Statutes & code83d ago- 2025 Form 760 Resident Individual Income Tax InstructionsFederal · Test KB83d ago
- 2025 Form 760 Resident Individual Income Tax InstructionsCalifornia · Statutes & code83d ago
- 2025 Virginia Schedule A InstructionsFederal · Test KB83d ago
Federal, every state and territory
Federal law sits alongside state and territory law: statutes and code, administrative regulations, revenue department guidance, and forms and instructions, all searchable together.
Height is document count. Color is breadth: statutes and code, regulations, guidance, forms and instructions. Hover a state for its numbers; click to pin it.
- 1 source type
- 2 source types
- 3 source types
- All 4 source types
Federal
Not yet covered
- Documents
- 1,023
- Passages
- 13,999
- California Revenue and Taxation Code923 docs
- IRS forms27 docs
- IRS WD25 docs
- IRS RB24 docs
- 2026 Form 1096IRS forms · Sep 10, 2026
- Form 434 (8-2026)IRS forms · Sep 10, 2026
- Form 14157 (Rev. 8-2026)IRS forms · Sep 10, 2026
Every answer traces back to the law
Feather cites the exact passage behind each claim: the document, its pages and a link to the source, so a reviewer can check the support in one click and the work holds up in an audit.
Primary law only
The knowledge base holds the Code, Treasury regulations, IRS guidance, Tax Court opinions and state law. No blogs, forums or secondary summaries.
Pinpoint, not general
A citation points to the passage and the PDF pages it came from, with a link to the original document.
The right tax year
Every passage keeps its publication date, and ranking favors the tax year the question asks about.
Can an S corp shareholder deduct a home office?
Subsection (a) shall not apply to any item to the extent such item is allocable to a portion of the dwelling unit which is exclusively used on a regular basis (A) as the principal place of business for any trade or business of the taxpayer...
- Source
- 26 U.S. Code § 280A(c)(1)
- Type
- Federal · Statutes & code
- Link
- law.cornell.edu/uscode/text/26/280A
Build with Feather
The knowledge base behind every Feather answer, inside your product and your agents: the same corpus, the same search, the same citations. Access is provisioned per customer.
API
Search and cite tax law over HTTPS.
Send a question and get back the passages that answer it, each with its source, link and page numbers.
MCP
The knowledge base as an agent tool.
Claude, Cursor or your own agent researches tax law in one tool call. No retrieval code to write.
citationSearch-mcp({
query: "S corp shareholder home office",
jurisdiction: "us-federal"
})
→ { sources: [{ type: "knowledge-base",
title, url, content, pageNumbers }] }Questions
What is the Feather Tax Knowledge Base?
It is the corpus of primary tax law that Feather, the AI Tax Assistant for CPAs, searches and cites when it answers a question. Feather crawls, parses and indexes it itself, and the same knowledge base is available to other products through an API and an MCP server.
Which sources does it include?
Federal sources include the Internal Revenue Code (Title 26), Treasury regulations from the eCFR, IRS rules and proposed rules in the Federal Register, Internal Revenue Bulletins, IRS forms, instructions and publications, written determinations, IRS news releases, disaster relief notices, section 7520 rates, and US Tax Court opinions and rules. State and territory sources include statutes and code, administrative regulations, revenue department guidance, and forms and instructions.
How large is it?
As of Nov 4, 2026, 10:34 AM UTC, it holds 1,023 source documents across 3 jurisdictions and 9 knowledge bases, split into 13,999 citable chunks.
How often is it updated?
Each source has its own crawler that runs on a recurring schedule; IRS sources are re-crawled weekly. Unchanged documents are skipped, revised ones replace the version they supersede, and new documents are indexed automatically. The counts on this page are read live from production.
What makes the citations audit-ready?
Every passage in the knowledge base comes from a primary source and keeps its title, publication date, page numbers and a link to the original document. A Feather answer cites the passage behind each claim, so a reviewer can verify it directly against the law.
How does search work?
Search is hybrid: vector similarity and full-text matching run together, the results are merged and then reranked, and ranking favors the tax year the question asks about. It returns passages, not whole documents, so each result is citable on its own.
Can I use the knowledge base in my own product?
Yes. The API returns the passages that answer a question, each with its source, link and page numbers, and the MCP server gives AI agents the same search as a tool. Access is provisioned per customer.
What is MCP?
The Model Context Protocol is an open standard for connecting AI agents to tools. Feather exposes knowledge base search as an MCP tool, so Claude, Cursor or your own agent can research tax law in one call and get back cited passages.