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Signal MCP

by googlarz
OverviewSchemaSourceRelated ServersDiscussionsAdmin
Python
Local

block_contact

Block a Signal contact to permanently stop incoming messages and calls. The blocked sender is not notified, and existing history remains intact. Reversible via unblock_contact.

Instructions

Block a Signal contact so they can no longer send you messages or call you. Only works when signal-mcp is the account's primary device — fails with 'This command doesn't work on linked devices' if signal-mcp was set up via signal-cli link. The block is applied locally via signal-cli and propagated to the Signal network. The blocked contact receives NO notification — from their perspective, messages appear sent but are silently discarded before reaching you; delivery receipts are suppressed. Blocking does not delete existing message history; prior conversations remain in your local store. The block persists across restarts and is reversible — call unblock_contact to lift it. Use when you want to permanently stop receiving messages from a contact. Use unblock_contact to reverse the block. Do NOT use as a temporary mute — blocking hides the contact from normal message flow entirely. Do NOT use to remove a contact from your list — use remove_contact for that.

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
numberYesPhone number to block (E.164 format, e.g. +1234567890)

Schema Changelog

Changes observed during successful MCP inspections.

  1. Changed1 schema field changedv0.1.2
    • changedInput schema / properties / number / description
      Previous value: -"Phone number to block"New value: +"Phone number to block (E.164 format, e.g. +1234567890)"
  2. First observedv0.1.0

TDQS

A4.6/5.0
Behavior5/5

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

With no annotations, the description fully discloses behavior: primary-device restriction, failure mode on linked devices, local application and network propagation, silent discard of messages, suppressed delivery receipts, no notification to blocked contact, preservation of history, persistence across restarts, and reversibility. This is exhaustive and leaves no surprises for the agent.

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?

The description is a single well-structured paragraph that front-loads the core purpose, then logically proceeds to limitations, effects, and usage guidance. While dense, every sentence contributes essential information; it could be slightly tightened but is far from verbose or redundant.

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 single-parameter tool with no output schema, the description covers all necessary context: prerequisites (primary device), side effects (silent discard, receipt suppression), persistence, reversibility, and clear boundaries with sibling tools. An agent can call this tool correctly with full knowledge of consequences.

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

Parameters3/5

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

The single parameter 'number' is fully described in the schema with E.164 format and example. Since schema coverage is 100%, the description adds no further parameter-specific detail beyond what the schema already provides, which meets the baseline of 3.

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 description clearly states the action (block a Signal contact), the resource (a contact), and the effect (can no longer send messages or call). It also explicitly distinguishes from unblock_contact and remove_contact, making sibling differentiation immediate.

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

Usage Guidelines5/5

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

Provides explicit when-to-use (permanently stop receiving messages), when-not-to-use (temporary mute, removing a contact), and names the alternative tools (unblock_contact, remove_contact). No ambiguity about appropriate contexts.

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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