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Signal MCP

by googlarz
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Python
Local

pin_message

Pin a message in a Signal DM or group to highlight it prominently for all participants, replacing the previous pinned message. Requires target_author and target_timestamp to identify the message.

Instructions

Pin a message in a DM or group conversation so it appears prominently in the conversation header. Pinning delivers a system-level pin notification to all participants via signal-cli; they see the pinned message highlighted at the top of the thread. Any participant can pin any message — admin privileges are not required. Only one message can be pinned per conversation at a time; pinning a new message automatically replaces the previous pin. Provide exactly one of recipient (for a DM) or group_id (for a group). Get target_author and target_timestamp from get_conversation — both are required to identify the message. Use unpin_message to remove a pinned message without replacing it. Use when you want to highlight an important message for all participants. Do NOT use if you only want to bookmark a message for yourself — pinning is visible to everyone.

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
group_idNoGroup ID for group conversations — provide this OR recipient
recipientNoPhone number for DM conversations — provide this OR group_id
target_authorYesPhone number of the message author (E.164)
target_timestampYesTimestamp of the message to pin (from get_conversation)

Schema Changelog

Changes observed during successful MCP inspections.

  1. Changed4 schema fields changedv0.1.2
    • changedInput schema / properties / group_id / description
      Previous value: -"Group ID for group conversations"New value: +"Group ID for group conversations — provide this OR recipient"
    • changedInput schema / properties / recipient / description
      Previous value: -"Phone number for DM conversations"New value: +"Phone number for DM conversations — provide this OR group_id"
    • changedInput schema / properties / target_author / description
      Previous value: -"Phone number of the message author"New value: +"Phone number of the message author (E.164)"
    • changedInput schema / properties / target_timestamp / description
      Previous value: -"Timestamp of the message to pin"New value: +"Timestamp of the message to pin (from get_conversation)"
  2. First observedv0.1.0

TDQS

A4.5/5.0
Behavior4/5

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

Without annotations, the description discloses side effects (system notification, replacement of previous pin), permissions (any participant), and the fact that only one pin exists per conversation. Could mention reversibility, but overall good.

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 informative with 9 sentences, each adding value. It is front-loaded with the main purpose. Could be slightly trimmed but still efficient.

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

Completeness4/5

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

For a mutation tool with 4 parameters and no output schema, the description covers purpose, side effects, prerequisites, and usage guidance. Leaves no major gaps.

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 covers all parameters (100%), so baseline is 3. The description adds value by specifying mutual exclusivity of recipient/group_id and sourcing target_author and target_timestamp from get_conversation.

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 tool pins a message in a DM or group conversation, making it prominent. It distinguishes from the sibling tool 'unpin_message' by explicitly mentioning it for removal.

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 ('highlight an important message for all participants') and when-not-to-use ('do NOT use if you only want to bookmark for yourself'), plus prerequisites (get target_author and target_timestamp from get_conversation).

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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