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Signal MCP

by googlarz
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Python
Local

update_contact

Idempotent

Set a private local name, nickname, or note for a Signal contact; changes sync to your linked devices and stay hidden from the contact.

Instructions

Set your private local name, nickname or note for another contact; it is synced to your own linked devices and never shown to the contact. To change your own public profile use update_profile; to block or delete a contact use block_contact or remove_contact. number (required, E.164). Pass at least one of: name (full display name; stored as given name and clears the family name unless family_name is also given), given_name, family_name, nick_given_name, nick_family_name (nickname shown instead of their profile name), note (private note). Fails if none is given or the number is not registered on Signal. Returns status, number and name. For a disappearing-message timer use set_expiration_timer.

Input Schema

NameRequiredDescriptionDefault
nameNoDisplay name to set
noteNoPrivate note about the contact
numberYesPhone number in E.164 format
given_nameNoContact given name
family_nameNoContact family name
nick_given_nameNoNickname given name
nick_family_nameNoNickname family name

Schema Changelog

Changes observed during successful MCP inspections.

  1. Changed6 schema fields changedv1.40.1
    • addedInput schema / properties / family_name
      Added value: +{
+  "description": "Contact family name",
+  "type": "string"
+}
    • addedInput schema / properties / given_name
      Added value: +{
+  "description": "Contact given name",
+  "type": "string"
+}
    • addedInput schema / properties / nick_family_name
      Added value: +{
+  "description": "Nickname family name",
+  "type": "string"
+}
    • addedInput schema / properties / nick_given_name
      Added value: +{
+  "description": "Nickname given name",
+  "type": "string"
+}
    • addedInput schema / properties / note
      Added value: +{
+  "description": "Private note about the contact",
+  "type": "string"
+}
    • changedInput schema / required
      Previous value: -[
-  "number",
-  "name"
-]New value: +[
+  "number"
+]
  2. First observedv0.1.0

TDQS

A4.9/5.0
Behavior5/5

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

Annotations cover the safety profile (readOnly=false, destructive=false, idempotent=true), and the description adds non-obvious behavior on top: the change is local-only, synced to your linked devices, never visible to the contact, and setting 'name' silently clears family_name unless family_name is also supplied. That side-effect disclosure is exactly the kind of trait structured fields cannot convey.

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-loaded with the core purpose and alternatives, and every sentence carries information. Slightly dense with nested parentheticals in the parameter list, but appropriate for a 7-parameter tool in a crowded sibling namespace.

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?

With no output schema, the description supplies the return shape ('status, number and name'), the failure modes, the exclusivity constraint, and the local-only scope. Nothing needed to invoke it correctly is missing.

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

Parameters5/5

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

Schema coverage is 100% (baseline 3), but the description goes well beyond it: it supplies the E.164 format, the cross-field rule that at least one optional field must be passed, and semantic distinctions the schema lacks (name vs. given/family name interaction, nickname 'shown instead of their profile name').

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 (set) and resource (private local name/nickname/note for another contact) and immediately contrasts it with update_profile, block_contact and remove_contact. An agent can distinguish it from every nearby sibling without opening a schema.

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?

Explicitly routes alternatives: update_profile for your own public profile, block_contact/remove_contact for blocking or deleting, set_expiration_timer for timers. It also states the precondition ('Pass at least one of...') and two failure conditions (no field given, number not registered).

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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