Yaktool for AI agents

Agents keep rewriting the same ad-hoc validators — and each one misses the edge cases. yaktool-mcp puts all 70 Yaktool checks inside your agent: the same rule engine as this site, with every check numbered, severity-graded and backed by an official source.

Install

Claude Code

claude mcp add yaktool -- npx -y yaktool-mcp

Claude Desktop

Add to claude_desktop_config.json:

{
  "mcpServers": {
    "yaktool": { "command": "npx", "args": ["-y", "yaktool-mcp"] }
  }
}

Cursor and other MCP clients

Any stdio-capable MCP client works — the command is npx -y yaktool-mcp. Requires Node.js ≥ 20. Package: yaktool-mcp on npm.

Why not just let the agent write a validator?

Deterministic — pure rule code. Same input, same result, every run.
Complete — the edge cases quick scripts miss (Excel scientific-notation damage, lost leading zeros, in-store barcode ranges, ISBN Bookland prefixes) are exactly what these rules cover.
Local & private — runs over stdio on your machine. Zero network calls; nothing leaves the host.
Structured — findings come back as { ruleId, severity, message, fix?, sourceUrl? }, not prose.
Bulk-native — most tools accept up to 1000 values per call, so a whole spreadsheet column is one call, not a loop.

All 70 tools

Every tool mirrors a check you can also run in the browser — same engine, same rules, same results.

validate_gtin

Validate a GTIN / UPC / EAN barcode
calculate_check_digit

Calculate / complete a GTIN check digit
analyze_amazon_search_terms

Analyze Amazon backend search terms (byte budget + rules)
convert_gtin

Convert a GTIN between UPC-12, EAN-13 and GTIN-14
validate_google_feed

Validate a Google Shopping product feed before upload
validate_shopify_csv

Validate a Shopify product CSV before importing
validate_isbn

Validate and convert an ISBN (10 ⇄ 13)
lint_listing_title

Check a product title against marketplace rules
check_main_image

Check product-image measurements against Amazon main-image rules
convert_upc_e

Convert UPC-E ⇄ UPC-A (zero suppression)
interpret_eight_digit_barcode

Disambiguate an 8-digit barcode (UPC-E vs GTIN-8)
detect_invisible_characters

Find and explain invisible or look-alike characters in text
identify_tracking_carrier

Identify the carrier from a tracking number
generate_barcode_modules

Generate the module pattern for a barcode symbol
validate_vin

Validate a VIN check digit and decode its structure
validate_imei

Validate an IMEI or IMEISV
validate_container_number

Validate a shipping container number (ISO 6346)
parse_gs1_element_string

Parse a GS1-128 element string into its Application Identifiers
diff_product_feeds

Compare two product feed versions aligned by SKU
fix_mojibake

Diagnose and repair encoding damage (mojibake)
detect_csv_dialect

Detect the delimiter, quoting and encoding traits of a CSV
check_number_format

Check a price or number for ambiguous formatting
check_date_format

Check a date for ambiguity, or decode a spreadsheet serial
diagnose_excel_damage

Diagnose what a spreadsheet broke in a column of data
check_gs1_digital_link

Check a GS1 Digital Link URI against the current standard
build_gs1_digital_link

Build a conformant GS1 Digital Link URI from a GTIN
check_image_metadata

Check an image for privacy-leaking EXIF metadata
check_country_code

Check or convert an ISO 3166-1 country code
check_hreflang

Check hreflang annotations and produce the block every page must carry
validate_awb

Validate an air waybill number
detect_mixed_script

Find characters that are not what they look like
convert_units

Convert dimensions or weights for a feed, and report what rounding costs
check_utm

Check a set of campaign URLs for tagging problems and report fragmentation
build_utm_url

Build a correctly tagged campaign URL
check_colour_space

Check whether an image is CMYK, RGB, greyscale or indexed
generate_slug

Turn product titles into URL slugs and platform handles
check_product_jsonld

Validate Product structured data, values included
build_product_jsonld

Generate Product JSON-LD that passes validation
check_description_html

Check product description HTML for what a marketplace will strip
check_postcode

Check postcodes against the format each country uses
check_lithium_battery

Calculate lithium battery watt hours and the passenger-carriage band
validate_gs1_key

Validate SSCC-18 and GLN numbers
validate_media_codes

Validate ISSN journal numbers and ISRC recording codes
validate_regulated_codes

Verify CAS Registry numbers and convert NDC drug codes
validate_iban

Validate IBANs and SWIFT/BIC codes
validate_tax_ids

Check EU VAT numbers and EORI numbers against their published formats and check digits
lint_bullet_points

Check listing bullet points and screen them for risky claim language
audit_column

Find duplicate and inconsistently written values in a column
calculate_dim_weight

Dimensional weight and the break-even box size
check_compliance_statement

Check Prop 65, allergen and CE/UKCA/FCC statement wording
check_open_graph

Check Open Graph meta tags
check_email_template

Check email merge fields before a send
check_textile_label

Check garment fibre content and care wording
audit_media_specs

Audit a batch of images and videos against marketplace limits
convert_shoe_size

Convert shoe sizes from the unit definitions
explain_apparel_sizing

Explain why apparel sizes cannot be converted
lookup_un_number

Look up dangerous goods entries by name or UN number
check_incoterm

Check an Incoterms trade term against the transport mode
validate_marketplace_feed

Validate a product feed for Meta, TikTok Shop, Walmart or Amazon
check_invoice_sequence

Find gaps and duplicates in a column of invoice numbers
check_peppol_invoice

Check a UBL invoice against the published Peppol BIS Billing 3.0 rules
convert_feed

Convert a product feed between Google Shopping and Meta
repair_feed

Repair a damaged product feed
check_hs_code

Check an HS / HTS / CN commodity code
check_origin_declaration

Check a preferential origin declaration against the prescribed wording
check_supplier_declaration

Pick and check an EU supplier's declaration
check_lei

Check the structure and check digit of an LEI
identify_einvoice

Identify an e-invoice XML: syntax, kind, profile, and which validator applies
check_creditor_reference

Check an ISO 11649 RF creditor reference
check_xrechnung

Check a German XRechnung invoice against KoSIT's official BR-DE rules