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WhatsMCP: MCP for WhatsApp

by com.whatsmcp.app
OverviewDiscussionsAdmin

React to Message

wa_react

React to a WhatsApp message with an emoji. Pass an empty reaction to remove a reaction you previously sent.

Input Schema

NameRequiredDescriptionDefault
chatYesthe chat the message is in — a phone number or a group JID; reacting to a channel (@newsletter) message is not supported
senderNogroup chats only: the phone number or JID of whoever sent the original message; omit in a DM or for your own message
reactionYesthe emoji to react with; an empty string removes a reaction you previously sent
account_idNothe account, as returned by wa_list_accounts; omit it when the workspace has only one account
message_idYesWhatsApp's id for the message, as returned by wa_send_message or seen in wa_list_messages

Output Schema

NameRequiredDescriptionDefault
statusYesok (the operation succeeded) or refused (nothing was done)
refusalNopresent only when status is refused
new_message_idNoWhatsApp's id for the react/edit/revoke protocol message itself

Schema Changelog

Changes observed during successful MCP inspections.

  1. Changed3 schema fields changed
    • changedInput schema / properties / account_id / description
      Previous value: -"the account, as returned by wa_list_accounts"New value: +"the account, as returned by wa_list_accounts; omit it when the workspace has only one account"
    • changedInput schema / required
      Previous value: -[
-  "account_id",
-  "chat",
-  "message_id",
-  "reaction"
-]New value: +[
+  "chat",
+  "message_id",
+  "reaction"
+]
    • addedOutput schema / properties / refusal / properties / candidates
      Added value: +{
+  "description": "on an account_ambiguous refusal: the accounts to choose from — retry with one of these as account_id",
+  "items": {
+    "additionalProperties": false,
+    "properties": {
+      "account_id": {
+        "description": "the id to retry with as account_id",
+        "type": "string"
+      },
+      "name": {
+        "description": "the account's WhatsApp display name",
+        "type": "string"
+      },
+      "phone": {
+        "description": "the account's phone number, E.164",
+        "type": "string"
+      },
+      "status": {
+        "description": "whether the number works right now — live, connecting, or why not, as wa_list_accounts reports it",
+        "type": "string"
+      }
+    },
+    "required": [
+      "account_id"
+    ],
+    "type": "object"
+  },
+  "type": [
+    "null",
+    "array"
+  ]
+}
  2. Changed3 schema fields changed
    • addedOutput schema / properties / refusal / properties / account_status
      Added value: +{
+  "description": "when the number is not working: its status — starting, not_running, whatsapp_down, suspended, pairing, unlinked or locked",
+  "type": "string"
+}
    • addedOutput schema / properties / refusal / properties / account_status_reason
      Added value: +{
+  "description": "the detail of account_status, e.g. no_egress, stopped, no_plan",
+  "type": "string"
+}
    • addedOutput schema / properties / refusal / properties / since
      Added value: +{
+  "description": "when the number stopped working, RFC3339, when known",
+  "type": "string"
+}
  3. First observed

TDQS

A3.6/5.0
Behavior3/5

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

Annotations already declare readOnlyHint=false, destructiveHint=false and idempotentHint=false, so safety is partly covered. The removal-by-empty-string behavior is genuinely useful context, but it is duplicated verbatim in the reaction parameter's schema text, and nothing is said about visibility to other participants or the channel limitation documented only in the schema.

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

Conciseness5/5

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

Two short sentences, front-loaded with the core action and followed by the one non-obvious modifier. No filler.

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?

With a complete input schema, an output schema and annotations present, the description only needs to nail purpose and the removal semantics, which it does. Minor gaps (channel-message restriction, group `sender` requirement) are covered by the schema rather than the description.

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?

Schema description coverage is 100%, so all five parameters (including the tricky group-only `sender` and the `account_id` fallback) are already fully documented in the schema. The description adds no parameter-level meaning beyond that, which is the expected baseline.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose4/5

Does the description clearly state what the tool does and how it differs from similar tools?

States a specific verb (react) and resource (a WhatsApp message) plus the emoji detail, which cleanly separates it from message-sending siblings like wa_send_message. It never names a sibling for comparison, so it stops short of full differentiation.

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

Usage Guidelines3/5

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

The second sentence usefully explains how to undo a reaction (empty string), which is a real usage cue. But there is no explicit when-to-use/when-not guidance, no mention of prerequisites (e.g. channel messages unsupported) and no pointer to alternatives such as wa_send_message or wa_delete_message.

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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