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US Treasury / IRS regulations (26 CFR, 'Treas. Reg.') — a thin, keyless wrapper over the official eCFR API, scoped to Title 26 (Internal Revenue Code regulations).
Two well-defined tools with strong descriptions (194 - 250 chars each) and complete JSON schemas. Both tools have clear, actionable descriptions that explain WHAT they do, WHEN to use them, and what they return. Input parameters are typed and described. However, output schemas are not documented, LLMs cannot predict response structure. No error handling guidance (e.g., 'citation not found' recovery). No tool annotations (readOnlyHint). Parameter descriptions could be more prescriptive about format constraints (e.g., citation format examples are in the tool description, not the parameter itself).
Get the full text of one Treasury Regulation / IRS regulation — a US federal tax regulation codified in 26 CFR — by its citation. Returns the exact regulatory wording currently in force. Answers "what does Treas. Reg. 1.170A say", "what is the IRS regulation for X", "the Treasury Regulation on X", "read 26 CFR 1.61-1", "the income tax regulation for X". Forgiving citation input: "1.170A-1", "26 CFR 1.61-1", "Treas. Reg. 1.501(c)(3)-1", "§1.170A-1", even "1.170A-1(b)" (trailing paragraph stripped). Tax citations are dotted — the part is the number BEFORE the first dot: "1.170A-1" -> part 1, section 170A-1; "301.7701-1" -> part 301. Covers 26 CFR part 1 income tax regulations (gross income, deductions, credits, charitable contributions 1.170A, exempt organizations 1.501(c)(3)-1, depreciation, capital gains), part 301 procedure & administration, parts 20 & 25 estate & gift tax, part 31 employment tax — the whole of Title 26. Pass a whole part (e.g. "1") to get a (large) section list. Example: tax_regulation({ citation: "1.170A-1" }) -> charitable contribution deduction; tax_regulation({ citation: "Treas. Reg. 1.61-1" }) -> gross income defined. Keyless.
Keyword search across federal tax regulations — US Treasury / IRS regulations in 26 CFR. Answers "what tax regulations cover X", "the IRS regulation / Treasury Regulation about X", "find the federal tax rule for X". Great for topics: charitable contribution deduction, gross income, business expense deduction, depreciation and MACRS, capital gains and losses, section 501(c)(3) exempt organizations, S corporations, partnerships, like-kind exchanges, employment tax, estate and gift tax, foreign tax credit, retirement plans. Returns matching Treasury Regulations with citation (26 CFR / Treas. Reg.), heading, excerpt, and source URL. Example: tax_search({ query: "charitable contribution deduction" }); tax_search({ query: "depreciation", limit: 15 }). Keyless.
Output schemas not documented. LLMs cannot predict response structure (fields, types, pagination). Agents must guess whether results include URLs, excerpts, citations, or all three.
No error handling guidance. If citation is invalid or not found, tool description does not explain recovery path (e.g., 'Try tax_search() to find the correct citation').
Missing tool annotations. Both tools are read-only (no state mutation), but lack readOnlyHint annotation. Agents cannot distinguish safe tools from destructive ones without explicit hints.
Parameter 'limit' in tax_search lacks explicit min/max constraints in schema. Description says '1-20 (default 10)' but JSON Schema has no minimum/maximum properties. LLMs may pass invalid values.
| Scored | Grade | Overall | Spec posture | Rubric |
|---|---|---|---|---|
| 2026-09-23 | C | 62 | 2026-07-28+ | v2 |
Transport unknown. Source code shows eCFR API calls but no explicit MCP transport layer (HTTP, SSE, STDIO) visible. Cannot verify remote accessibility or protocol compliance.