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mcp-signal

mcp-signal

by Sealjay
OverviewSchemaSourceRelated ServersDiscussionsAdmin
Python
Local

Send Message

send_message

Send a Signal text message to a direct recipient or group via signal-cli. Delivers real messages programmatically; rate-limited to 1 message per recipient per second.

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

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

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

A4.6/5.0
Behavior5/5

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

Goes well beyond the annotations (readOnlyHint=false, openWorldHint=true, idempotentHint=false, destructiveHint=false). It discloses irreversibility ('Sends are not reversible from this server'), that deletion is only via official clients, concrete rate limits (1 per recipient per second, 10 per 60s globally), the external dependency on signal-cli/SIGNAL_ACCOUNT, and the success return fields.

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

Conciseness4/5

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

Front-loads the one-line purpose, then layers constraints, rate limits, prerequisites, and return info in short discrete sentences. It is longer than minimal but every sentence carries a distinct operational fact; only minor trimming is possible.

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?

An output schema exists, yet the description still name-checks the success payload (target_type, target identifier, timestamp). Combined with constraints, rate limits, and prerequisites, an agent has everything needed to call this correctly.

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 baseline is 3, but the description adds the crucial exactly-one-recipient rule and states that zero or more than one raises an error — stricter information than the schema's 'mutually exclusive' notes and not derivable from the required list (only message is required).

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?

States a specific verb and resource (send a text message via Signal) plus the two target types (direct recipient or group). This clearly separates it from read_messages, search_messages, and chat_activity among the siblings.

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?

Gives an explicit prerequisite: signal-cli and SIGNAL_ACCOUNT must be configured, and the agent should call get_status first to verify send_available is true. It does not explicitly name alternative send paths or exclusion cases, but the precondition guidance is concrete and actionable.

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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