Willitsend MCP server

willitsend

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.

Try it in the browser: runs client-side, nothing leaves the page.

npx -y -p github:abryfs/willitsend willitsend-cli "Hey! Your appointment is tomorrow at 2pm." --first-message

Verdict: BLOCK
Segments: 1 (gsm7, 41 septets)
Channel: unknown
[BLOCK] first-message.opt-out: First message doesn't include opt-out instructions (e.g. "Reply STOP
to unsubscribe"). Carriers may silently filter first messages that lack one, with no API error.
  Fix: Append "Reply STOP to unsubscribe." to the message body.
  Source: https://docs.agentphone.ai/documentation/reference/messaging-rate-limits#first-message-requirements
[WARN] first-message.opt-in: No opt-in acknowledgment language found …
[INFO] first-message.brand: No brand_name was provided …

The problem

Messaging APIs report "sent" when a message reaches the downstream carrier, not when it reaches a phone. AgentPhone's rate-limit docs spell out the consequence: first messages that skip brand identification, opt-in acknowledgment, or opt-out instructions "may be silently filtered by carriers. The API will not return an error."

AI agents now send texts autonomously, and nothing sits between the model and the carrier. An agent that drops the opt-out line gets no error and no delivery. An agent that adds one emoji turns a 160-character message into three billable segments and never notices.

willitsend is the missing check: a deterministic, stateless lint for a draft message. Text and context in, verdict and evidence out. It sends nothing and stores nothing.

sequenceDiagram
    participant A as AI agent
    participant W as willitsend
    participant API as Messaging API
    participant C as Carrier
    participant P as Phone

    rect rgba(255,69,58,0.08)
    note over A,P: without preflight
    A->>API: send_message (no opt-out language)
    API-->>A: "sent" ✓
    C--xP: silently filtered. no error, no delivery
    end

    rect rgba(52,199,89,0.08)
    note over A,P: with preflight
    A->>W: preflight_message(draft, context)
    W-->>A: BLOCK · missing opt-out · fix + citation
    A->>W: preflight_message(fixed draft)
    W-->>A: PASS
    A->>API: send_message
    API-->>A: "sent" ✓
    C->>P: delivered
    end

Why not just prompt the rules into your agent?

A fair question: AgentPhone's docs are agent-readable, so you could feed them into every generation call and ask the model to comply. Two things break, and one gets expensive:

1. Generation is probabilistic; verification is deterministic. A model with the rules in context complies usually. This checker returns the same verdict every time, and its failure mode is a visible finding rather than a silently filtered message. Compose-time guidance and pre-send verification are complements — this repo ships both (the agent skill is the compose-time half).
2. Models can't do segment math. Septet counting, GSM-7 extension characters, encoding flips from one smart quote, placement-aware packing — token-based models are structurally bad at exactly this arithmetic. No amount of prompting fixes it; a 300-line deterministic function does.
3. The token math, measured (char-count/4 heuristic on the actual pages, July 2026):

Shortened. The full README is on GitHub.