Vonage Messages API + MCP by Vonage (Ericsson)

# Fix list: Vonage Messages API + MCP

From Anchor Terminal's listing at https://www.anchorterminal.com/tools/vonage, the October 2026 research run, assessed 1 October 2026. Grade B, 67.1 out of 100.

This is everything the published grade says the listing lacks, the biggest possible gain to the total first. It comes from the reason given for each score, the checklist each category was scored against (https://www.anchorterminal.com/benchmark/#checklist), the provenance checks, the deductions, what we couldn't check and what the review panel asked for. A fix counts at the next check, once it's public.

For a coding agent working on Vonage Messages API + MCP: work through the items below in the product, its docs and its public pages. Each category gives the reason for its score, with the points each checklist item earned, and the checklist itself, so the gap is the items that earned less than their points. Change the product, not the wording, and keep a note of what you changed and where it's published.

## 1. Agent ergonomics, 50 out of 100, up to 8.1 more on the total

Why it scored 50: The Messages API sends and updates messages and returns a message_uuid. Lists and searches live in the separate Reports API (15 of 25). Filtering only through Reports (10 of 20). A shared error catalogue with codes an agent can look up (15 of 20). No idempotency key on sends, and channel-level rejections arrive later by status webhook after a 202 (0 of 20). SDKs in Node, Python and four more languages. Basic auth works for sends, but application webhooks need a JWT application (10 of 15).

The checklist (https://www.anchorterminal.com/benchmark/#checklist-ergonomics):

- 0 to 25, context cost. For MCP, the number and size of the tool definitions (25 for ten or fewer compact tools, 15 for 11 to 30, 5 for more than 30, plus up to 10 back for toolsets, dynamic loading or read-only subsets). For APIs, whether responses can be sized (field selection, limits, summaries).
- 20, pagination, filtering and output-size controls.
- 20, actionable, documented error responses, codes and messages an agent can recover from.
- 20, idempotency or safe retries, and for MCP the `readOnlyHint` and `destructiveHint` annotations.
- 15, sensible defaults, few required parameters, and official SDKs in at least two languages.

Models are read for tool use, structured output, prompt caching, context length, batch and SDKs. Frameworks for how much code and how many defaults a tool-calling agent with MCP needs.

## 2. Payments & pricing, 37 out of 100, up to 7.9 more on the total

Why it scored 37: No x402, MPP or L402 (0). The pricing page loaded on 2 October. Messenger is $0.0011 per delivered message, while SMS, MMS, RCS and WhatsApp rates appear per country through a selector or a downloadable sheet, with no login, and Viber is custom (17 of 20). Free trial with no card, per the pricing page, and €2 of test credit per the 30 September check (20). A person signs up in a browser (0).

The checklist (https://www.anchorterminal.com/benchmark/#checklist-payments):

The published rubric, also on the [x402 page](https://www.anchorterminal.com/x402/).

- 40, a machine payment protocol (x402, MPP or L402) on the tool's own endpoints. 10 to 30 when it covers only some endpoints or only goes through a third party, and the note says which.
- 20, per-call or per-unit pricing published without a login. 10 for public plan-only pricing, 0 for "contact sales" or prices behind a login.
- 20, a free tier or trial that doesn't need a card.
- 20, autonomous onboarding, meaning an agent can get access without a person signing up in a browser (keyless use, x402, a programmatic key API).

Payment platforms and agent wallets rarely charge for their own API over a machine protocol, so the first line has steps for them, and the highest one that applies counts. 40 when x402, MPP or L402 runs on all their own endpoints, 30 when it runs on part of their own API, 25 when their merchants can accept one, 20 for running a facilitator, 15 for paying as a buyer, and 0 when the only protocol is their own. Merchant acceptance sits above a facilitator because the platform's own customers can charge agents through it, while a facilitator settles for sellers who wire up the protocol themselves. The counter-argument (a facilitator does more for the protocol as a whole) has a point. Each note says which step applied.

Open-source software you run yourself is scored on its hosted or paid option if it has one. A free, self-hosted package with nothing to buy gets 20, 20 and 20 for the last three lines, and 0 to 40 for the first only if it ships a payment protocol.

## 3. Security & auth, 73 out of 100, up to 4.7 more on the total

Why it scored 73: Sends can be authorised with an application JWT signed RS256, whose ACL claim limits paths and methods and whose lifetime runs from 30 seconds to 24 hours, or with Basic auth on the account key and secret (30). JWT ACLs can narrow a token, with no confirmation step for sends (15 of 20). Inbound messages are untrusted text. Webhooks carry an HS256 JWT with a payload_hash of the body, and we found no prompt-injection guidance (5 of 15). Message records through the Reports API, which the MCP's get-records-report tool calls, and an Audit API that monitors the account through events, priced at $550 a month on the pricing page (13 of 15). The security page says Vonage holds ISO 27001, PCI-DSS, SOC, HITRUST and CSA STAR across its product lines without saying which cover the Communications APIs, and links a CSA STAR registry entry. No security.txt, disclosure policy or bug bounty found (10 of 20).

The checklist (https://www.anchorterminal.com/benchmark/#checklist-security):

- 0 to 30, the credential model. 30 for OAuth 2.1 with scopes, or scoped and revocable keys with rotation. 20 for plain revocable API keys. 10 for one all-powerful key. 10 off when a secret can travel in a URL query string as a documented option.
- 0 to 20, read-only or least-privilege modes, and confirmation or approval for destructive actions.
- 0 to 15, prompt-injection posture where the tool returns untrusted content (documented mitigations or guidance). A tool that returns no untrusted content gets 10.
- 0 to 15, audit logs or per-call visibility for the operator.
- 0 to 20, a security programme. security.txt or a disclosure policy, a bug bounty, SOC 2 or ISO 27001, advisories handled in public.

Models are read for retention, whether API data trains models (and whether that's off by default), zero-retention options and certifications. Frameworks for telemetry defaults, approval hooks, guardrails and sandboxing.

## 4. Reliability, 77 out of 100, up to 4.6 more on the total

Why it scored 77: Statuspage at vonageapi.statuspage.io with components and history (20). IsDown counts 106 incidents in 90 days, 1 major, which we couldn't tie to messaging. The SMS entries were single-carrier or single-country, such as T-Mobile delivery on a subset of 10DLC numbers for about 6 hours on 1 October and AT&T short code delivery for about 5 hours on 29 September, so minor (20). The Messages API allows 75 requests a second per API key by default (15). The OpenAPI spec documents 429 with Retry-After and X-RateLimit headers, without backoff or safe-retry guidance (12 of 15). No SLA found. vonage.com loaded on 2 October, and neither the legal hub nor the security page links one (0). The Messages API is generally available (10).

The checklist (https://www.anchorterminal.com/benchmark/#checklist-reliability):

Hosted APIs, MCP servers, models and platforms.

- 20, a public status page with component history (Statuspage, Instatus, BetterStack or the vendor's own).
- 0 to 30, the incident record for the last 90 days on that page. 30 for a clean record or trivial incidents only, 20 for minor incidents only, 10 for one major outage (an hour or more of a core API down, or errors across the board), 0 for several. 5 when there's no history we could read, and the note says so.
- 15, rate limits documented with numbers.
- 15, documented 429 or overload handling (Retry-After, backoff guidance), and idempotency keys or safe-retry guidance where writes are involved.
- 10, an SLA published for any paid tier.
- 10, the surface agents use is generally available, not beta or preview.

Local packages, SDKs, frameworks and stdio MCP servers.

- 20, installs from an official package with supported runtimes stated.
- 25, a public CI and test suite, passing on the default branch.
- 0 to 25, open crash or regression issues relative to activity (25 for few and handled, 0 for many, old and unanswered).
- 15, semver discipline and breaking changes called out in a changelog.
- 15, version 1.0 or later, or declared stable.

Protocols are read from their reference implementations, the public facilitators or servers, spec stability and test vectors.

## 5. Transparency & trust, 52 out of 100, up to 4.2 more on the total

Made of editorial 28, provenance 75.

Why it scored 52: Closed service. The API terms set the contracting entity by region in a schedule, and the terms body didn't render for our reader on 2 October either. The MCP server is Apache-2.0 (15). The legal hub links a Data Processing Addendum and HIPAA BAAs are sold as an add-on, but we found no retention periods, and the privacy policy page rendered only as a landing page (13 of 30). SDK deprecation warnings, but no dated deprecation policy found (0 of 20). No sub-processor list or data locations found on the legal hub, the security page or the DPA landing page (0).

The checklist (https://www.anchorterminal.com/benchmark/#checklist-transparency):

- 0 to 30, source availability and licence clarity. 30 for open source under an OSI licence, 15 for closed with clear terms, 0 for unclear terms.
- 0 to 30, data handling and retention statements that agree with each other (privacy policy, DPA, retention periods, subprocessors).
- 0 to 20, a deprecation policy or notices with dates.
- 0 to 20, telemetry disclosed with an opt-out (local software), or subprocessors and data locations disclosed (hosted).

The other half of Transparency and trust is the provenance score, computed from checked facts (below). The category score is the mean of the two.

Provenance checks not met in full (half of this category, computed from checked facts):

- Endpoint on the vendor's domain: api.nexmo.com is not on vonage.com (0 of 15)
- security.txt: not found (0 of 10)

## 6. Maintenance & community, 80 out of 100, up to 1.8 more on the total

Why it scored 80: vonage-python-sdk v4.9.0 tagged on 2026-09-16 (30). vonage-node-sdk v3.29.0, v3.30.0 and v3.30.1 and vonage-python-sdk v4.8.2 and v4.9.0 in the last 90 days (20). Closed service with a changelog index and a support site. We didn't sample issue replies (8 of 15). Official SDKs current in six languages (15). The MCP repo runs CI, but its last release was v1.5.1 on 2026-05-26 (7 of 10).

The checklist (https://www.anchorterminal.com/benchmark/#checklist-maintenance):

- 0 to 30, time since the last release, or the last published model or API change for a closed service. 30 within 30 days, 20 within 90, 10 within 180, 0 older.
- 20, at least three releases or dated changelog entries in the last 90 days.
- 0 to 25, responsiveness. Issues and pull requests answered on GitHub (the open issues and how recent the replies are). For closed services, a public changelog and a support or community channel that answers, 0 to 15.
- 15, presence in the official MCP registry under a verified namespace (MCP servers), or current official SDKs (APIs and models).
- 10, package health, current dependencies and CI.

Models are read for deprecation notice periods and model churn rather than release counts.

## 7. Schema & documentation, 90 out of 100, up to 1.6 more on the total

Why it scored 90: OpenAPI 3.0.3 spec for the Messages API, version 1.19.1 (25). llms.txt that tells agents to keep the api.nexmo.com hostnames and use the Messages API over the legacy SMS API (10). The reference explains each channel's message types, with less on when not to use one (14 of 20). Typed fields from the spec (12 of 15). Examples per channel and a shared API error catalogue (14 of 15). Versioned /v1 path, a versioned spec and a public changelog index (15).

The checklist (https://www.anchorterminal.com/benchmark/#checklist-schema):

APIs and MCP servers.

- 25, a machine-readable contract (a public OpenAPI file or similar; for MCP, typed JSON Schema inputs on every tool).
- 10, llms.txt or Markdown docs served for agents.
- 0 to 20, descriptions that say what a tool is for, when to use it and when not to, read from the tool definitions in the source or the API reference.
- 0 to 15, typed inputs with enums, constraints and required fields, and no free-form JSON blobs.
- 0 to 15, examples and documented error responses.
- 15, versioning and a public changelog.

Models are read from the API reference, the OpenAPI file, llms.txt, the structured-output and tool-use docs and the model cards. Frameworks from docs a model can follow, typed interfaces, examples and the API reference.

## What we couldn't check

What we couldn't read counted as absent. Publishing it on a page a plain HTTP fetch can read (not only in a browser) lets the next check count it.

- unchecked: the API terms body (contracting entity by region, any SLA or notice periods) and the full privacy policy and DPA text. The pages loaded on 2 October but their bodies didn't render for our reader
- Which of the listed certifications cover the Communications APIs
- Whether Vonage itself supports the Vonage-Community MCP package. Its README doesn't say, and its server.json names the io.github.Vonage-Community registry namespace at version 1.2.0 while npm is at 1.5.1
- Per-country SMS, WhatsApp and RCS prices, which need the country selector

## Weaknesses

- No idempotency key, and channel rejections arrive only by status webhook after a 202
- The sending MCP lives in the Vonage-Community GitHub organisation, last released on 2026-05-26, with no tool annotations
- SMS, WhatsApp and RCS prices sit behind a country selector, and the terms body doesn't render without a browser
- No SLA, security.txt, sub-processor list or retention periods found
- The Audit API costs $550 a month

## What costs an agent a turn today

The notes we give agents before they call it. Each one is a workaround an agent shouldn't need.

- Keep api.nexmo.com as the host, don't rewrite it to vonage.com
- Use the Messages API, not the legacy SMS API
- Treat a 202 as accepted only, and wait for the status webhook before assuming delivery
- Use JWT auth if you need inbound or status webhooks, Basic auth doesn't deliver to application webhooks
- Verify the webhook JWT and its payload_hash against the raw body

## What the review panel asked for

- Publish a rate table
- Quantify the WhatsApp platform fee
- Add idempotency keys
- Publish an SLA

## When it's done

Send what changed and where it's published as a dispute (https://www.anchorterminal.com/builders/#disputes, or `POST https://www.anchorterminal.com/api/v1/contact` with `"kind": "dispute"`). Disputes are answered in public, and the listing is checked again by the same checklist. Paying for an audit or a listing claim changes nothing here.