The classification corpus

Every layer is legally relevant.
Every layer must be evaluated.

The HTSUS is not a flat list of headings. It is a layered legal instrument — eleven distinct levels of authority, each governing a different aspect of classification. Add the CBP regulatory corpus and you have fifteen layers that a complete classification must account for.

HTSUS Corpus 11 layers · Published by USITC
01
General Rules of Interpretation (GRI)
Six mandatory rules governing how every product is classified. Applied in sequence — GRI 1 first, escalating only when the prior rule does not fully resolve the classification. The applicable GRI determines the classification method.
02
Additional U.S. Rules of Interpretation
Four supplemental rules specific to U.S. law. Rule 1(b) governs functional use classifications; Rule 1(c) addresses textiles; Rule 1(d) covers sets. These apply alongside the GRI and are not optional.
03
General Notes
Foundational rules applying to the tariff schedule as a whole — country of origin requirements, duty-free treatment programs (GSP, USMCA, CAFTA-DR), and definitions that govern the entire HTSUS. General Note 3 alone contains dozens of operative provisions.
04
Section Notes
Notes governing an entire section of the HTSUS (Sections I–XXI). Section XV Note 3 defines base metals for all of Chapters 72–83. Section XVI Note 4 defines machines. Section notes can mandate or exclude classification across multiple chapters.
05
Chapter Notes
Notes governing a single chapter. Chapter notes define scope ("this chapter does not cover…"), classify parts and accessories, establish material composition thresholds, and override heading text. Under GRI 1, chapter notes are evaluated before any heading.
06
Subheading Notes
Notes applying only within a specific heading's subheading structure — not to the chapter as a whole. Subheading Note 1 to Chapter 71 defines "alloys" for precious metals. Subheading notes are separate from chapter notes and govern a narrower, more specific scope.
07
Additional U.S. Notes
Chapter-level notes specific to U.S. law — not part of the international HS. Additional U.S. Notes define terms, set quantity thresholds, and establish rate conditions (e.g., tariff-rate quota triggers) that are entirely absent from the WCO Harmonized System.
08
Headings
The 4-digit level — the primary organizing unit of the HTSUS. Heading text is evaluated under GRI 1 after all applicable notes have been screened. The heading that specifically describes the product, as modified by applicable notes, governs.
09
Subheadings
The 6-digit and 8-digit levels. Subheading comparison is governed by GRI 6 — the GRI apply, in order, only among subheadings at the same level. Subheading notes apply at this stage. The 8-digit classification is the last level shared internationally.
10
Chapters 98 and 99
Special classification provisions unique to U.S. law. Chapter 98 covers returning U.S. goods, educational and scientific instruments, and other duty-preference provisions. Chapter 99 is the vehicle for all temporary duty modifications — Section 301, Section 232, IEEPA tariffs. A complete classification must check Chapter 99 overlay applicability after the base code is established.
11
Statistical Suffixes
The 9th and 10th digits. Not duty-determinative but required for a valid entry. Statistical suffixes track import data by product characteristics — size, composition, form. An 8-digit classification is incomplete for U.S. Customs entry purposes.
CBP Regulatory Corpus 4 sources · Binding on CBP
Administrative Rulings Binding
Rulings issued by CBP on classification, valuation, and origin. Published in the CROSS database. A ruling on the same or substantially identical merchandise is binding on CBP at the port of entry and authoritative for the importer who received it.
📋
Binding Rulings Binding
Advance rulings requested by an importer before importation. Binding on CBP at the port of entry for the specific importer and merchandise described. A binding ruling in hand is the strongest available protection against adverse classification at entry.
Revocations
CBP may revoke a prior ruling — prospectively, or retroactively with notice. Reliance on a revoked ruling, without awareness of the revocation, is not protected. Active revocations must be monitored against in-use classifications.
Modifications
CBP may modify a ruling's legal basis or narrow its scope without full revocation. Modifications affect the conditions under which a prior ruling remains valid. A classification supported by an unmodified ruling is differently positioned than one supported by a modified ruling.

Why the regulatory corpus matters

A classification that is correct under the HTSUS but contradicts an active CBP ruling on substantially identical merchandise is a classification that will not hold. The regulatory corpus is not supplementary material — it is authority.

Sequence is not optional

The right corpus
and the right order.

Having access to the corpus is necessary but not sufficient. Each layer governs at a different level of specificity, and the precedence relationships between them are legally defined. A tool that evaluates heading text before screening chapter notes has applied the law backwards. A classification that identifies a correct heading but fails to check applicable Chapter 99 overlays is an incomplete entry.

Kanon applies each layer in the sequence CBP applies them — and records not just the outcome but which layer was determinative at each step. This is what allows a classification to be reconstructed, explained, and defended.

Precedence relationships the law defines
Notes take precedence over heading text. Under GRI 1, a chapter or section note that excludes a product from a heading governs — regardless of how well the heading text describes it.
Subheading notes apply only within their heading. A subheading note does not modify classification at the 4-digit level — it governs only the subheading comparison that follows.
Additional U.S. Notes are layer-specific. An Additional U.S. Note applies within a chapter. It does not modify section notes or GRI provisions — its scope is defined by its placement.
Chapter 99 applies after the base classification. Special duty provisions in Chapter 99 overlay the base HTS code. They are evaluated as a second pass — after the Chapters 1–97 classification is established.
CBP rulings are authoritative within their scope. A ruling issued on substantially identical merchandise is evaluated against the current classification — and its revocation status must be confirmed.

User-in-the-loop classification

No black boxes.
Every decision point is explicit.

Kanon does not produce a code. It produces a classification — a chain of explicit determinations, each grounded in a specific layer of the corpus, each visible to the user who is responsible for the entry.

At each decision point, the user can see the provision being applied, the product attribute it is being applied to, and the outcome. Factual determinations that the engine derived — rather than received from explicit product data — are flagged so the user can confirm or correct them. Confirmed determinations are recorded with the user's identity and timestamp.

This is what makes the classification auditable. Not a logged output — a transparent process in which the human expert remains in control at every determinative step.

Classification in progress — Stainless Steel Ball Valve User review active
Section XV Note 3 — Base metals
Valve body is 316 stainless steel. Section XV scope confirmed — base metals section applies. Alloy classification rules do not trigger.
Confirmed
Ch. 84 Note 2 — Parts exclusion
Product is a complete standalone component, not a part of a larger named machine. Note 2 exclusion does not apply.
Confirmed
Assembly configuration — inferred
Engine inferred: product is a complete standalone component, not a sub-assembly. Attribute not explicitly stated — user confirmation requested.
⚡ Confirm?
Heading 8481 — Taps, cocks, valves
GRI 1 resolves at heading level. Product is specifically described by heading 8481 text. No competing heading identified.
Confirmed
Chapter 99 overlay check
Checking active Section 301 provisions and IEEPA tariffs against 8481.80.3090. Country of origin: China.
Pending

Legally substantiated

Every determination
documented at the moment it is made.

The Classification Support Package Kanon generates at the moment of classification is an immutable record. It captures every corpus layer evaluated, the outcome of each evaluation, the product attributes driving factual determinations, the HTSUS corpus version in effect, and the identity of every user who confirmed a determination.

This record is generated when the classification is made — not reconstructed when a CBP inquiry arrives. The distinction matters: a retroactively assembled rationale is not the same as contemporaneous documentation. Kanon produces the latter.

CBP asks
Which notes were evaluated, and what did each one say about this product?
Kanon records: every section note, chapter note, subheading note, and Additional U.S. Note screened, with the condition evaluated and the outcome at each step.
CBP asks
Was the classification made under the tariff schedule in effect at the time of entry?
Kanon records: the exact HTSUS corpus version pinned to the classification. If a new edition was published between classification and entry, the impact is identified.
CBP asks
Were applicable Chapter 99 provisions evaluated?
Kanon records: every Chapter 99 overlay checked against the base code, the active duty provisions identified, and the country-of-origin determination that triggered or excluded each.
CBP asks
Are there any CBP rulings on this merchandise, and were they considered?
Kanon records: any CROSS rulings evaluated against the product, their current status (active, revoked, modified), and the determination of applicability.

How Kanon compares

Corpus coverage is where
most tools stop short.

Corpus layer evaluated General-purpose AI HTSUS lookup tools Kanon
GRI (all six, in sequence)
Additional U.S. Rules of Interpretation
General Notes Partial / inconsistent
Section Notes Partial / inconsistent
Chapter Notes Partial / inconsistent Manual lookup
Subheading Notes
Additional U.S. Notes
Chapter 99 overlay evaluation
Statistical suffixes (full 10-digit) Often 6-digit only Varies
CBP binding rulings / revocations
Immutable CSP with full reasoning trace
Pinned to a versioned corpus Training data cutoff Typically unversioned

See the full corpus in action.
Classify a product — free.

No account required. Describe a product and watch Kanon evaluate the corpus — every layer, in the right order — and show you the reasoning at each step.