Deterministic pre-send lint for SMS/iMessage: silent carrier filtering and segment blowups.
Deterministic pre-send lint for SMS/iMessage: silent carrier filtering and segment blowups. Exposed over MCP by the willitsend mcp server, that capability becomes something an assistant can invoke while it works, not something you go and do afterwards.
Your AI agent sends texts. Carriers silently drop the non-compliant ones, and the API never tells you. willitsend is the missing check between the model and the carrier: a deterministic preflight for outbound SMS/iMessage that catches silent filtering, segment blowups, and dropped iMessage features before you spend the send.
Everything the assistant can do here goes through one of these:
Segment — math parity:** agrees with Twilio's reference segment calculator on encoding and segmentLatency — ** median ~4µs per message, ~100,000 messages/second on one thread (Node 22, Apple Silicon laptop; single-pass code-point tables, zero per-characterApproach — Tokens per messageRule — Severitywillitsend on npm is all you need. Most clients run it directly, so configuration is a few lines and a restart.
You will need one environment variable: AGENTPHONE_API_KEY. The server will not start without them, which is usually why the tools fail to appear on a first run. Keep credentials in your client's env block or a secrets manager rather than in a file you might commit.
Plenty of developer tooling servers cover similar ground. The differences that matter in practice are scope of access and how much setup stands between you and a working tool call. Willitsend's toolset — Segment, Latency, Approach and 1 more — is a fair guide to whether it matches your workflow. It is maintained by abryfs; worth a glance at recent repository activity before you build anything load-bearing on it.
SyncDev reviews every entry in this directory against the project's own documentation before publishing, and revisits them as servers change.
| Tool | What it does |
|---|---|
| Segment | math parity:** agrees with [Twilio's reference segment calculator](https://github.com/TwilioDevEd/message-segment-calculator) on encoding and segment count across a frozen 126-vector corpus: GSM-7/UCS-2 boundaries, exten |
| Latency | ** median ~4µs per message, ~100,000 messages/second on one thread (Node 22, Apple Silicon laptop; single-pass code-point tables, zero per-character allocation). Run npm run bench on yours. Preflighting every outbound me |
| Approach | Tokens per message |
| Rule | Severity |
{
"mcpServers": {
"willitsend": {
"command": "npx",
"args": ["-y", "-p", "github:abryfs/willitsend", "willitsend-mcp"]
}
}
}Configuration as documented by the project. Restart the client after saving.
| Variable | Description | Required |
|---|---|---|
| AGENTPHONE_API_KEY | Credential the server authenticates with. | Yes |
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