# 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. Category scores, facts, verdicts and agent notes side by side.

- Canonical: https://www.anchorterminal.com/compare/fonoa-vs-kintsugi
- Markdown: https://www.anchorterminal.com/compare/fonoa-vs-kintsugi.md (~2,250 tokens)
- Slim: https://www.anchorterminal.com/compare/fonoa-vs-kintsugi.min.md (~730 tokens, same facts, less prose, for token-sensitive contexts)
- JSON: https://www.anchorterminal.com/compare/fonoa-vs-kintsugi.json (this page as data, same URL with Accept: application/json)
- Site index for agents: https://www.anchorterminal.com/llms.txt (full text: https://www.anchorterminal.com/llms-full.txt)
- API: https://www.anchorterminal.com/api/v1/index.json
- Updated: 2026-10-08

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

- Fonoa: grade D, 51.7/100, rank #575 of 722. Markdown https://www.anchorterminal.com/tools/fonoa.md · JSON https://www.anchorterminal.com/api/v1/tools/fonoa.json
- Kintsugi: grade C, 60.7/100, rank #392 of 722. Markdown https://www.anchorterminal.com/tools/kintsugi.md · JSON https://www.anchorterminal.com/api/v1/tools/kintsugi.json

## 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

| Category | Weight | Fonoa | Kintsugi | Edge |
| --- | --- | --- | --- | --- |
| Reliability | 16% (20 this run) | 66 | 73 | Kintsugi +7 |
| Performance | 10%, pending | pending | pending | not scored in this run |
| Schema & documentation | 13% (16.2 this run) | 68 | 87 | Kintsugi +19 |
| Agent ergonomics | 13% (16.2 this run) | 64 | 75 | Kintsugi +11 |
| Security & auth | 14% (17.5 this run) | 47 | 52 | Kintsugi +5 |
| Payments & pricing | 10% (12.5 this run) | 3 | 13 | Kintsugi +10 |
| Task success | 10%, pending | pending | pending | not scored in this run |
| Maintenance & community | 7% (8.8 this run) | 49 | 78 | Kintsugi +29 |
| Transparency & trust | 7% (8.8 this run) | 48 | 60 | Kintsugi +12 |
| Negative events | ≤15 | 0 | -3 | |
| **Total** | | **51.7 · D** | **60.7 · C** | |

## Facts side by side

| Fact | Fonoa | Kintsugi |
| --- | --- | --- |
| Kind | HTTP API | HTTP API |
| Vendor | Fonoa Technologies Limited | Kintsugi AI, Inc. |
| Hosted endpoint | `https://api.fonoa.com` | `https://api.trykintsugi.com` |
| Transports | HTTP | HTTP, Streamable HTTP |
| Auth | API key | OAuth or key |
| Pricing | Paid | Paid |
| x402 | no | no |
| Licence | Proprietary service. The API contract is not published. The public Terms of Service took effect on 14 May 2020 and name older seller sites | Proprietary service under the Kintsugi Terms of Service. The Python SDK repository is MIT |
| Tools exposed | none | 55 |
| Read-only variant documented | no | yes |
| llms.txt | yes | yes |
| Last release | 2026-10-02 | 2026-10-07 |
| Terms last updated | no document linked | 2026-09-29 |
| Privacy policy last updated | no date given | 2025-04-13 |
| Customer content may train models |  | yes |
| Terms restrict automated access |  | yes |
| Terms restrict benchmarking |  | yes |
| Terms or service can change without notice |  | not found in the text |
| Arbitration or class-action waiver |  | yes |
| Popularity | none | 71 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.


## For agents

- This comparison as JSON: https://www.anchorterminal.com/compare/fonoa-vs-kintsugi.json, and with the fewest tokens: https://www.anchorterminal.com/compare/fonoa-vs-kintsugi.min.md
- Over MCP at https://www.anchorterminal.com/mcp (no key): `compare_tools {"a": "fonoa", "b": "kintsugi"}`. From a terminal: `anchor compare fonoa kintsugi`
- Each listing in full: https://www.anchorterminal.com/api/v1/tools/fonoa.json and https://www.anchorterminal.com/api/v1/tools/kintsugi.json

## Other comparisons with Fonoa or Kintsugi

- [Anrok vs Fonoa](https://www.anchorterminal.com/compare/anrok-vs-fonoa.md)
- [Anrok vs Kintsugi](https://www.anchorterminal.com/compare/anrok-vs-kintsugi.md)
- [Avalara AvaTax vs Fonoa](https://www.anchorterminal.com/compare/avalara-vs-fonoa.md)
- [Avalara AvaTax vs Kintsugi](https://www.anchorterminal.com/compare/avalara-vs-kintsugi.md)
- [Fonoa vs Numeral](https://www.anchorterminal.com/compare/fonoa-vs-numeral.md)
- [Fonoa vs Quaderno](https://www.anchorterminal.com/compare/fonoa-vs-quaderno.md)
- [Fonoa vs TaxCloud](https://www.anchorterminal.com/compare/fonoa-vs-taxcloud.md)
- [Fonoa vs TaxJar](https://www.anchorterminal.com/compare/fonoa-vs-taxjar.md)
- [Fonoa vs Vertex O Series](https://www.anchorterminal.com/compare/fonoa-vs-vertex-tax.md)
- [Fonoa vs Zamp](https://www.anchorterminal.com/compare/fonoa-vs-zamp.md)
- [Kintsugi vs Numeral](https://www.anchorterminal.com/compare/kintsugi-vs-numeral.md)
- [Kintsugi vs Quaderno](https://www.anchorterminal.com/compare/kintsugi-vs-quaderno.md)
- [Kintsugi vs TaxCloud](https://www.anchorterminal.com/compare/kintsugi-vs-taxcloud.md)
- [Kintsugi vs TaxJar](https://www.anchorterminal.com/compare/kintsugi-vs-taxjar.md)
- [Kintsugi vs Vertex O Series](https://www.anchorterminal.com/compare/kintsugi-vs-vertex-tax.md)
- [Kintsugi vs Zamp](https://www.anchorterminal.com/compare/kintsugi-vs-zamp.md)