Head to head · Tax calculate · October 2026 research run
Fonoa vs Numeral
Fonoa scores 51.7 (D) on agent readiness against Numeral's 49.3 (D), and leads in 2 of 7 scored categories. Numeral leads on schema & documentation, agent ergonomics, payments & pricing and maintenance & community. Both do tax calculate.
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.
Ahead on
- Reliability, 66 against 25
Watch for
No self-serve signup. Sandbox, demo and production keys are issued by Fonoa after contact by email or the sales form
Numeral D
Good for An agent working for a seller or platform that has a Numeral account and needs tax at checkout, committed transactions for filing, and read access to nexus, registrations and filings through MCP.
Ahead on
- Schema & documentation, 87 against 68
- Agent ergonomics, 71 against 64
- Payments & pricing, 10 against 3
- Maintenance & community, 60 against 49
Watch for
No status page, uptime SLA or numeric rate limit was found. The product page says rate limits can be removed on request
Score by category
| Category | Weight this run | Fonoa | Numeral | Edge |
|---|---|---|---|---|
| Reliability | 16%20 | 66 | 25 | Fonoa +41 |
| Performance | 10%pending | pending | pending | not scored in this run |
| Schema & documentation | 13%16.2 | 68 | 87 | Numeral +19 |
| Agent ergonomics | 13%16.2 | 64 | 71 | Numeral +7 |
| Security & auth | 14%17.5 | 47 | 47 | even |
| Payments & pricing | 10%12.5 | 3 | 10 | Numeral +7 |
| Task success | 10%pending | pending | pending | not scored in this run |
| Maintenance & community | 7%8.8 | 49 | 60 | Numeral +11 |
| Transparency & trust | 7%8.8 | 48 | 45 | Fonoa +3 |
| Negative events | ≤15 | 0 | 0 | |
| Total | 51.7 · D | 49.3 · D |
Facts side by side
| Fact | Fonoa | Numeral |
|---|---|---|
| Kind | HTTP API | HTTP API |
| Vendor | Fonoa Technologies Limited | Numeral Two, Inc. |
| Hosted endpoint | https://api.fonoa.com | https://api.numeralhq.com |
| Transports | HTTP | HTTP, Streamable HTTP |
| Auth | API key | API 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 Numeral's terms of service. The Go, Python and Node SDKs are Apache-2.0 |
| Tools exposed | none | 14 |
| Read-only variant documented | no | yes |
| llms.txt | yes | yes |
| Last release | 2026-10-02 | 2026-09-15 |
| Terms last updated | no document linked | no date given |
| Privacy policy last updated | no date given | no document linked |
| Customer content may train models | not found in the text | |
| Terms restrict automated access | not found in the text | |
| Terms restrict benchmarking | not found in the text | |
| Terms or service can change without notice | not found in the text | |
| Arbitration or class-action waiver | yes | |
| Popularity | none | 0 stars, 9 npm/wk, 19 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.
Numeral
Docs are written for agents, with a public OpenAPI spec for 32 operations, Markdown pages, llms.txt and a remote MCP server whose 14 tools are read-only by default. No status page, numeric rate limit or SLA was found, the API ignores idempotency keys, and API access is sold on a custom plan after a demo.
Before you call either
Fonoa
- Send the key in the
Ocp-Apim-Subscription-Keyheader. Use the sandbox key at https://sandbox.fonoa.com and the production key at https://api.fonoa.com - Treat validations and e-invoicing submissions as asynchronous. POST, then poll the GET endpoint or wait for the webhook, and avoid tight polling
- Reuse the same
transaction_idon a retry of/v1/transactions. A transaction already processed is not processed again - Commit a calculation with POST
/tax/v2/calculations/<uuid>/commitonly when the sale is final. The commit adds it to revenue tracking - Ask the Fonoa contact to configure webhooks. There is no API for it, and always fetch
resource_urlas given in the webhook
Numeral
- Send
X-API-Version: 2026-03-01on every call tohttps://api.numeralhq.com. Merchant, platform and certificate endpoints reject requests without it - Commit with a stable
reference_order_id. OnREFERENCE_ORDER_ID_ALREADY_EXISTSlook up the existing transaction, becauseIdempotency-Keyis ignored - Commit before the calculation's
expires_at. If it has expired, calculate again and commit the newcalculation_idwith the originalreference_order_id - Send
amountas the line total in minor units to/tax/calculationsand as the per-unit price to/tax/platform/calculations - Start with an
sk_test_key. Certificate endpoints and MCP certificate tools are live only and answerTESTMODE_NOT_SUPPORTEDorlive_mode_required
Questions
Which is better for AI agents, Fonoa or Numeral?
Fonoa scores 51.7 (D) on agent readiness against Numeral's 49.3 (D), and leads in 2 of 7 scored categories. Numeral leads on schema & documentation, agent ergonomics, payments & pricing and maintenance & community.
Do Fonoa and Numeral need an API key?
Both need an API key.
Can an agent call Fonoa and Numeral without installing anything?
Yes. Fonoa has a hosted endpoint at https://api.fonoa.com and Numeral at https://api.numeralhq.com.
Other comparisons with Fonoa or Numeral
Machine-readable
- This page as Markdown
/compare/fonoa-vs-numeral.md· slim.min.md· JSON.json(or sendAccept: text/markdown) - Each listing in full
/api/v1/tools/fonoa.json·/api/v1/tools/numeral.json - From a terminal
anchor compare fonoa numeral(the CLI) - Over MCP
compare_tools {"a": "fonoa", "b": "numeral"}at/mcp, no key