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Signal MCP

by googlarz
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Python
Local

find_contact

Read-onlyIdempotent

Search local Signal contacts by name, number, nickname, or username to resolve a recipient's E.164 number before messaging or confirm a contact exists. Optionally include non-address-book recipients.

Instructions

Find contacts whose number, name, given/family name, nickname or username contains query (case-insensitive substring; required). Use it to resolve a name to an E.164 number before send_message, or to check that a contact exists; use list_contacts instead to list everyone or filter by blocked status. all_recipients (default false) also searches people outside your address book, e.g. group members known only by their profile name. Reads the local contact store only. Returns a list (possibly empty) of contact objects with number, uuid, name, given_name, family_name, about, blocked and display_name.

Input Schema

NameRequiredDescriptionDefault
queryYesCase-insensitive fragment of a name, nickname, username or phone number
all_recipientsNoAlso include recipients that are not in your address book (e.g. members of your groups), with their profile names

Schema Changelog

Changes observed during successful MCP inspections.

  1. Changed1 schema field changedv1.43.0
    • changedInput schema / properties / query / description
      Previous value: -"Name or phone number fragment to search for"New value: +"Case-insensitive fragment of a name, nickname, username or phone number"
  2. Changed1 schema field changedv1.40.1
    • addedInput schema / properties / all_recipients
      Added value: +{
+  "default": false,
+  "description": "Also include recipients that are not in your address book (e.g. members of your groups), with their profile names",
+  "type": "boolean"
+}
  3. Addedv1.33.3

TDQS

A4.6/5.0
Behavior4/5

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

Annotations already declare readOnlyHint, idempotentHint, openWorldHint=false and destructiveHint=false. The description adds genuinely new context: that it reads the local contact store only, that the result may be empty, and it enumerates the returned fields — behavior not derivable from the annotations. It stops short of discussing pagination or ordering, so not a 5.

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?

Dense but front-loaded: the matching rule and the query semantics come first, then routing, then the return shape. Every sentence carries information, though the run-on construction makes it slightly heavier than it needs to be.

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 compensates by enumerating the returned contact object fields and noting the list may be empty. Combined with the sibling routing and the local-store scope, an agent has everything needed to call and interpret this tool.

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 goes further by stating query is required and case-insensitive, and by explaining what all_recipients=false means in practice (group members known only by profile name). That example adds real meaning beyond the schema's phrasing.

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 (find) and resource (contacts) plus the exact matching fields (number, name, given/family name, nickname, username) and match semantics (case-insensitive substring). It also names the sibling it is not (list_contacts), so an agent can distinguish it without opening either 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 states when to use it (resolve a name to an E.164 number before send_message, or verify a contact exists) and when to use the alternative instead (list_contacts for listing everyone or filtering by blocked status). Both the positive and negative routing conditions are given.

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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