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mcp-signal

by Sealjay
OverviewSchemaSourceRelated ServersDiscussionsAdmin
Python
Local

send_message

Send a text message through Signal to a direct recipient or group. Specify exactly one target by phone number, group ID, or chat name.

Instructions

Send a text message via Signal to a direct recipient or group.

This is a write operation that delivers a real message through signal-cli. Sends are not reversible from this server — Signal supports user-initiated message deletion only via the official clients. Exactly one of phone_number, group_id, or chat_name must be supplied; providing zero or more than one raises an error. Rate-limited to 1 message per recipient per second and 10 messages per 60-second window globally. Requires signal-cli and SIGNAL_ACCOUNT to be configured — call get_status first to verify send_available is true. Returns target_type, target identifier, and timestamp on success.

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
messageYesThe text message content to send.
group_idNoTarget group ID as returned by list_groups. Mutually exclusive with phone_number and chat_name.
chat_nameNoExact chat name from list_chats; auto-resolves to the matching phone_number, service ID or group_id. Mutually exclusive with the other two recipient fields.
phone_numberNoRecipient phone number in E.164 format (e.g. '+441234567890'). Mutually exclusive with group_id and chat_name.

Output Schema

TableJSON Schema
NameRequiredDescriptionDefault

No arguments

Schema Changelog

Changes observed during successful MCP inspections.

  1. Changed1 schema field changedv0.2.1
    • changedInput schema / properties / chat_name / description
      Previous value: -"Exact chat name from list_chats; auto-resolves to the matching phone_number or group_id. Mutually exclusive with the other two recipient fields."New value: +"Exact chat name from list_chats; auto-resolves to the matching phone_number, service ID or group_id. Mutually exclusive with the other two recipient fields."
  2. Changed4 schema fields changedv0.1.3
    • addedInput schema / properties / chat_name / description
      Added value: +"Exact chat name from list_chats; auto-resolves to the matching phone_number or group_id. Mutually exclusive with the other two recipient fields."
    • addedInput schema / properties / group_id / description
      Added value: +"Target group ID as returned by list_groups. Mutually exclusive with phone_number and chat_name."
    • addedInput schema / properties / message / description
      Added value: +"The text message content to send."
    • addedInput schema / properties / phone_number / description
      Added value: +"Recipient phone number in E.164 format (e.g. '+441234567890'). Mutually exclusive with group_id and chat_name."
  3. First observedv0.1.2

TDQS

A4.7/5.0
Behavior5/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Beyond the annotations (readOnlyHint=false, idempotentHint=false), it discloses that sends are irreversible from this server, the exact rate limits (1/recipient/second, 10 per 60s global), the external dependency on signal-cli plus SIGNAL_ACCOUNT, and the success return fields. This is exactly the kind of context a write tool needs.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness5/5

Is the description appropriately sized, front-loaded, and free of redundancy?

Front-loaded with the action, then constraints, prerequisites, and return value in a tight sequence with no filler sentences. Every sentence carries operational information.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness5/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

For a four-parameter write tool, the description covers target selection, irreversibility, rate limits, configuration prerequisites, and result fields. With an output schema present, it need not detail return contents further, so nothing material is missing.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters4/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema coverage is 100%, so the baseline is 3, but the description adds error semantics not present in the schema: supplying zero or more than one recipient field raises an error, making the exactly-one constraint explicit rather than merely mutual exclusivity.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

The first sentence gives a specific verb (send), resource (text message), transport (Signal), and both supported target modes (direct recipient or group). This is unambiguous against siblings like read_messages, search_messages, and list_chats, which are all read/list operations.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines4/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

It states a concrete prerequisite (call get_status first to verify send_available is true) and the target-selection rule that exactly one of phone_number/group_id/chat_name must be set. It does not name alternatives for non-send cases or say when not to use this tool, so it stops short of the top tier.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

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