Send a WhatsApp text message

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

Annotations only say it's a write operation (readOnlyHint=false), non-idempotent, and destructive. The description adds far more: the MCP elicitation prompt with a cancel path, rate limits (5/min, 30/day), a pre-send state assertion that aborts on focused-chat mismatch, experimental group sends, and WhatsApp ToS restrictions. These are exactly the behavioral traits an agent needs to know but are absent from annotations.

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

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

The description is dense but every sentence earns its place: purpose + input provenance, confirmation gate, rate limits, state assertion, and legal constraint. It front-loads the core action and then logically layers caveats, with no filler.

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

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

For a mutation tool with two parameters and an output schema, the description covers prerequisites (how to get chat_id), operational behavior (prompt, rate limits, state check), limitations (experimental groups, legal prohibition), and usage ethics (sparingly, not marketing). An agent now has everything needed to decide and execute correctly without opening schemas.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Since schema description coverage is 0%, the description carries the burden. It effectively explains chat_id as an opaque identifier from specific lookup tools and clarifies that body is shown verbatim in the prompt. It doesn't specify body length limits or formatting, but for a simple string parameter this is adequate compensation.

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

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

The description states a specific verb and resource ('Sends a text message'), identifies the exact recipient type ('one resolved chat by opaque chat_id'), and distinguishes itself from siblings by emphasizing text vs. file and by referencing the lookup tools that produce chat_id. An agent can immediately tell this from send_file and read_chat.

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

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

It explicitly instructs that chat_id must come from search_contacts/list_chats and never a free-form name, which is strong usage guidance. It also warns against automated/bulk messaging and notes experimental group sends. It doesn't explicitly name alternatives like 'use send_file for files,' but the context is clear enough for correct tool selection.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.