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:

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".

Add an entry to _ALIASES in toolsearch.py:

"your_tool": "the words a user would actually say for this thing",

Write real phrasings. Do not copy strings out of the eval cases. An alias map tuned against its own answer key measures nothing.

4. Add an eval case

Append to tests/toolsearch-eval/cases.json:

{"q": "how someone would phrase the task", "gold": "your_tool", "alts": ["a genuinely correct substitute"]}

alts is for tools that would also be a right answer, not near misses. Then run the eval and confirm recall did not drop.

5. Verify

pytest
ruff check .

Then, against a live server, add a line to tests/smoke.sh and run it. A tool that has never been called over real HTTP is not done.

If the tool needs a new bridge endpoint

Add the handler in whatsapp-bridge/main.go, then a thin wrapper in whatsapp.py, then the tool in tools.py. Keep the wrapper thin: the query and retry logic belongs in whatsapp.py, the MCP-facing shape belongs in tools.py.

Rebuild with the FTS5 tag or the bridge crash-loops:

go build -tags sqlite_fts5 ./...