whatsapp-mcp-server: Skill for Claude Code

Adding an MCP tool

Five steps. Skipping step 3 or 4 produces a tool that exists but that the model can never find, which is the same as not shipping it.

1. Write the tool

Tools live in whatsapp-mcp-server/tools.py (general) or scheduling.py (queue, drafts, notes). Register with @mcp.tool(annotations=...) using one of the five constants defined at the top of tools.py:

Constant	For
READ_LOCAL	Reads the local store. No network, no side effect.
READ_BRIDGE	Reads via the bridge (touches the network), no side effect.
SEND	Sends a message or file, non-idempotent.
MUTATE	Changes state, recoverable (react, mark read, edit).
DESTRUCTIVE	Irreversible: delete, revoke, leave, block.

A DESTRUCTIVE tool takes confirm: bool = False and calls _require_confirm before doing anything:

@mcp.tool(annotations=DESTRUCTIVE)
def delete_thing(thing_id: str, confirm: bool = False) -> dict:
    """One-line summary the model reads.

    Args:
        thing_id: ...
        confirm: Must be True. The user, not the LLM, has to have agreed.
    """
    if (denied := _require_confirm(confirm)) is not None:
        return denied
    ...

The annotation is only a hint to the client. The confirm kwarg is the actual enforcement, and it exists because older MCP clients do not support elicitation.

Clamp every caller-supplied bound. The existing tools use limit <= 100, context windows <= 20, message body <= 65536 bytes. Match them.

2. Decide whether it belongs in the core set

_CORE_TOOLS in server.py is the 29-tool hot core served directly in the default minimal toolset. Every entry there is paid for on every request to the model, whether or not WhatsApp is touched.

The bar: would a typical session use this in the first three calls? If not, leave it out. It stays fully reachable through find_tool / call_tool. Most new tools should not be in the core.

3. Make it findable

If the tool's name and description do not share vocabulary with how a person would ask for it, find_tool cannot rank it. schedule_message never lexically matches "send this tomorrow morning".