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Head to head · Tax calculate · October 2026 research run

Fonoa vs Kintsugi

Kintsugi scores 60.7 (C) on agent readiness against Fonoa's 51.7 (D), and leads in every scored category. Both do tax calculate.

FonoaFonoa Technologies Limited · HTTP API D51.7/100#575 of 722 KintsugiKintsugi AI, Inc. · HTTP API C60.7/100#392 of 722

Which one, for what

Fonoa D

Good for An agent working for a company that already has a Fonoa contract and needs tax ID validation, VAT or GST calculation, or e-invoice reporting across many countries through one API.

Also in its favour

  • No incidents deducted, where Kintsugi loses 3 points for them

Watch for

No self-serve signup. Sandbox, demo and production keys are issued by Fonoa after contact by email or the sales form

Kintsugi C

Good for An agent working for a seller that already has Kintsugi Premium and wants estimates, transaction sync, exemptions, nexus, registrations and filing status through one API, or read-only answers about an account through the OAuth MCP server.

Ahead on

  • Reliability, 73 against 66
  • Schema & documentation, 87 against 68
  • Agent ergonomics, 75 against 64
  • Security & auth, 52 against 47
  • Payments & pricing, 13 against 3
  • Maintenance & community, 78 against 49
  • Transparency & trust, 60 against 48

Watch for

API access, SDKs and real-time tax calculation are listed only under Premium, which is priced on request. API keys need a paid plan that includes them

Score by category

CategoryWeight this runFonoaKintsugiEdge
Reliability16%206673Kintsugi +7
Performance10%pendingpendingpendingnot scored in this run
Schema & documentation13%16.26887Kintsugi +19
Agent ergonomics13%16.26475Kintsugi +11
Security & auth14%17.54752Kintsugi +5
Payments & pricing10%12.5313Kintsugi +10
Task success10%pendingpendingpendingnot scored in this run
Maintenance & community7%8.84978Kintsugi +29
Transparency & trust7%8.84860Kintsugi +12
Negative events≤150-3
Total51.7 · D60.7 · C

Facts side by side

FactFonoaKintsugi
KindHTTP APIHTTP API
VendorFonoa Technologies LimitedKintsugi AI, Inc.
Hosted endpointhttps://api.fonoa.comhttps://api.trykintsugi.com
TransportsHTTPHTTP, Streamable HTTP
AuthAPI keyOAuth or key
PricingPaidPaid
x402nono
LicenceProprietary service. The API contract is not published. The public Terms of Service took effect on 14 May 2020 and name older seller sitesProprietary service under the Kintsugi Terms of Service. The Python SDK repository is MIT
Tools exposednone55
Read-only variant documentednoyes
llms.txtyesyes
Last release2026-10-022026-10-07
Terms last updatedno document linked2026-09-29
Privacy policy last updatedno date given2025-04-13
Customer content may train modelsyes
Terms restrict automated accessyes
Terms restrict benchmarkingyes
Terms or service can change without noticenot found in the text
Arbitration or class-action waiveryes
Popularitynone71 npm/wk, 10 PyPI/wk

Verdicts

Fonoa

The API reference is served as Markdown with an OpenAPI definition on each endpoint page, and e-invoicing submissions are idempotent by transaction_id. API keys are issued by Fonoa staff after contact, no price, rate limit or changelog is published, and the only public terms date from May 2020 and cover older seller sites.

Kintsugi

The docs are built for machine readers, with llms.txt, Markdown pages, a public OpenAPI 3.1 file, a dated changelog and an MCP server whose 55 tools carry read-only and destructive annotations. API keys need the custom-priced Premium plan and carry no scopes, no general rate limit is published, and breaking changes reached the pinned 2026-07-21 release in October 2026.

Before you call either

Fonoa

  1. Send the key in the Ocp-Apim-Subscription-Key header. Use the sandbox key at https://sandbox.fonoa.com and the production key at https://api.fonoa.com
  2. Treat validations and e-invoicing submissions as asynchronous. POST, then poll the GET endpoint or wait for the webhook, and avoid tight polling
  3. Reuse the same transaction_id on a retry of /v1/transactions. A transaction already processed is not processed again
  4. Commit a calculation with POST /tax/v2/calculations/<uuid>/commit only when the sale is final. The commit adds it to revenue tracking
  5. Ask the Fonoa contact to configure webhooks. There is no API for it, and always fetch resource_url as given in the webhook

Kintsugi

  1. Send Api-Key and pin Api-Version (for example 2026-10-06) on Tenanted API calls to https://api.trykintsugi.com. Without the header a request runs against 2026-07-21
  2. Use x-api-key and x-organization-id with /v1 paths for the SDKs and the docs MCP server. They don't cover the Tenanted API
  3. Call POST /tax-estimations for a quote. Nothing is stored. Record the sale with a transaction create, which answers 202, then check processingStatus before reading tax totals
  4. Always send externalId on creates. A repeat with the same externalId and source returns the stored record with 200 and doesn't apply the new fields
  5. Branch on the error code, not the message. Retry 429, 500 and 503 with exponential backoff, and restart paging from the first page on stale_cursor

Questions

Which is better for AI agents, Fonoa or Kintsugi?

Kintsugi scores 60.7 (C) on agent readiness against Fonoa's 51.7 (D), and leads in every scored category.

Do Fonoa and Kintsugi need an API key?

Fonoa needs an API key. Kintsugi takes an API key or an OAuth sign-in.

Can an agent call Fonoa and Kintsugi without installing anything?

Yes. Fonoa has a hosted endpoint at https://api.fonoa.com and Kintsugi at https://api.trykintsugi.com.

Other comparisons with Fonoa or Kintsugi

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