Customer.io vs Sequenzy

Customer.io 75

Graded as a hosted service. Statuspage at status.customerio.com with nine components, re-read on 1 November, and incident history (20). The history page lists six incidents in the 90 days to 1 November 2026, all marked minor or none. Data processing delays for a small subset of US customers on 3 August (07:08 to 07:42 UTC), the interface on 5 August (26 minutes, none), the in-app Agent on 3 September (5 minutes), reduced delivery to Microsoft-hosted addresses on 4 September (Microsoft's incident, none), US sending delays on 19 September (27 minutes) and the workspace interface on 27 October (19:11 to 19:36 UTC, with processing and sending unaffected). The two July incidents marked major (20 and 31 July) left the window on 18 and 29 October, and with them the 5 points taken off for frequency, so minor only (20). Limits published with numbers, 10 requests a second on the App API, one every 10 seconds for API-triggered broadcasts, and a guideline of 3,000 requests per 3 seconds on Track and Pipelines that returns no 429 (15). 429 with Retry-After on the App API and automatic backoff in the CLI, but no idempotency key found for sends or other writes (10). No SLA found, and the terms promise commercially reasonable efforts (0). The APIs are generally available and the MCP docs carry no beta label. The CLI is at v0.0.36 (10). 20+20+15+10+0+10 = 75.

Sequenzy 38

Graded with the hosted lines. No status page was found; none is linked from the site, llms.txt or docs, and status.sequenzy.com doesn't resolve (0). With no history to read, the incident line takes 5. 429 responses carry RateLimit-Limit and RateLimit-Remaining headers for a per-minute policy, and some routes state numbers (20 requests a minute per workspace for AI copy), but no table of limits per key was found (8 of 15). 429s carry Retry-After, sends take an Idempotency-Key, a reused key with a different body returns IDEMPOTENCY_KEY_REUSED, and the MCP docs say a retry hint alone doesn't make a write safe to repeat (15). No SLA found (0). No beta label on the API or MCP server (10). Total 38.

Customer.io 83

Graded on the MCP server. Eight tools, with endpoint schemas fetched on demand through cio_schema in place of one tool per endpoint. cio_prime loads a reference at the start of a task, which costs some context (23). Filtering, pagination and auto-pagination on cio_read_api, and start and limit cursors on the App API (18). Tool errors are structured JSON, unknown fields return 422, and the CLI has stable exit codes (17). Reads, writes and deletes are separate tools and writes and deletes support dry-run previews. No idempotency keys, and we couldn't read the tool annotations without an account (10). Official libraries for Node, Python, Go and Ruby (15).

Sequenzy 69

The MCP tool reference lists about 306 tools, the over-30 band, and no toolsets, tool search or dynamic loading was found (5 of 25). List endpoints paginate and filter, and contact timelines use cursors (20). Errors carry a code, a human message, a fix and a docs link, with retryAfterSeconds when the API sent Retry-After (20). Idempotency keys on sends and event imports; MCP readOnlyHint and destructiveHint annotations weren't found in the published reference (14 of 20). Sensible defaults with a selected workspace; one official SDK (TypeScript) plus a CLI (10 of 15). Total 69.

Customer.io 79

OAuth with dynamic client registration, PKCE, five scopes and a revocation endpoint, per-user sessions that can't exceed the user's role, and service account tokens with expiry, a permanent read-only option and exchange for one-hour JWTs. On 1 November the authorisation server metadata lists only the S256 PKCE method, where on 17 October it also listed plain, so the 2 points taken off for it come back. The public and private keys introduced on 30 October split browser keys (pk_, no sends or reads) from server keys (sk_), and keys are rotated by adding a new one and revoking the old. A private key has no per-key scopes and works with every API, sends and deletes included, so as with grist, cal-com and calendly (scoped OAuth beside a full-access key) we take 2 off. Service account tokens can be read-only or limited by role, and expire (28). Connections default to read. Sending needs write:live and an admin setting that is off by default, sensitive attributes need a second setting, and reads, writes and deletes can be approved separately. No server-side approval step once live writes are allowed (18). Profile attributes and events are customer-written. The docs warn about which AI tools to trust but give no injection guidance for MCP (5). Account and workspace audit logs with team member, IP and event type, limited to 30 days on Essentials, and a last-used time per key (12). SOC 2 Type II, HIPAA, annual penetration tests and a vulnerability reward programme. No security.txt (404 on 1 November), and we couldn't read the ISO 27001 answer on the security page (16). 28+18+5+12+16 = 79.

Sequenzy 67

Workspace and account API keys with fine-grained permission scopes, presets and explicit *:delete rights, revocable in settings, plus an OAuth service_auth flow for agents with user confirmation (30). Read-only and drafts-only presets let an agent prepare mail without sending, and account keys keep the user's workspace role (20). The agent inbox and reply tracking give the agent inbound mail, and no prompt-injection guidance was found in the MCP, permissions or inbox docs (4 of 15). The DPA lists administrative audit logs and MCP events report replies and bounces; no per-call API log for the customer was found (8 of 15). A responsible disclosure address on the security page, no security.txt (404), bug bounty or certification (5 of 20). Total 67.

Customer.io 86

Public OpenAPI 3.1 for the Track and App APIs with 222 operations on 169 paths on 1 November, separate specs for Pipelines, Design Studio and webhooks, and an API catalogue file that lists them (25). llms.txt, per-section indexes, and Markdown for any page by adding .md (10). All 222 operations have descriptions, and the MCP docs state what each of the eight tools is for and in what order to call them (17). 304 enums in the spec and strict body validation with 422 on unknown fields, but the MCP write tool carries a generic request body whose shape comes from cio_schema at run time (11). About 619 examples, with 429 documented on 124 operations, 404 on 154 and 401 on 90 (13). Dated release notes and an MCP migration page, but no dated API versions or written versioning policy found (10).

Sequenzy 95

OpenAPI 3.1 at docs.sequenzy.com/openapi.yaml with 349 paths and 475 operations, all described (25). llms.txt on both hosts, llms-full.txt, auth.md, agents.md and Markdown twins of the docs (10). Operation and tool descriptions give purpose, the scope each needs and the alternative, such as the deprecated generate-sequence alias (18 of 20). Typed inputs, and tools reject undeclared arguments with an error naming the supported ones (13 of 15). Errors on nearly every operation (401 on 442, 404 on 330, 400 on 290) with examples, and a structured error with code, howToFix and docsUrl for tools (14 of 15). Version in the path and spec, and a dated changelog (15). Total 95.

Customer.io 76

Closed service with published terms, revised August 2026 (re-read 1 November). The CLI source is public under Apache 2.0 with the Commons Clause, which isn't an OSI licence, and the Claude Code plugin is MIT (15). Privacy policy revised August 2026 and a DPA effective September 2026 that deletes company data at termination on request. The AI settings page says customer data isn't used to train models. Retention is stated as the length of the agreement, with no numbered periods (22). The MCP migration page documents the May 2026 tool changes and a 30-day window on request. The 30 October key change says existing credentials keep working, with no end date. No general API deprecation policy found (8). Sub-processor list revised October 2026 with purposes and locations, US and EU regions, and 10 days' notice of changes in the DPA (20).

Sequenzy 67

A closed service. The SDK, MCP server and CLI are MIT on npm. The terms (30 June 2026) don't name the contracting entity in their text or a governing jurisdiction; the footer names Nic Tech Solutions, LLC (15 of 30). Privacy policy of 16 September 2026 and a public DPA agree on processing, and the terms say data is deleted within 30 days of termination (24 of 30). Deprecated endpoints are marked and kept as compatibility aliases; no written deprecation policy with notice periods (10 of 20). The DPA names its core sub-processors with their purpose; data locations aren't stated (15 of 20). Total 64.

Customer.io 45

No x402, MPP or L402 (0). Public plan prices with per-unit overage, Essentials from $100 a month, $0.009 per additional profile and $0.12 per additional 1,000 emails. Premium starts at $1,000 and Enterprise is priced by sales, so 15 of 20. A free 14-day trial, per the plan features page. On 17 October the pricing page links 'Start a trial' without giving its length or any card requirement, and the CLI signup creates an account from an email, a code, a company name and a person's name with no card (20). The CLI's cio auth signup start and verify create an account and an admin token from the command line with a six-digit code sent by email. That needs an inbox but no browser. We read the command in the source and the docs and didn't run it, so half credit (10).

Sequenzy 40

No x402, MPP or L402 (0). Prices are public as volume tiers from $19 for 15,000 emails to $2,999 for 5 million, without a per-email overage rate (10 of 20). Free plan of 2,500 emails a month with no card (20). Agents can register through service_auth, but the user has to confirm a code in a Sequenzy browser page, and plan payment is through Stripe (10 of 20). Total 40.