call_extension

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

No annotations are provided, so the description carries the full burden. It usefully discloses prerequisites (target enabled and externally_connectable) and the no-tabs-open behavior. However, it does not explain what happens on failure, whether a response from the target is returned, or whether the message is fire-and-forget, which are important behavioral traits for an agent invoking this tool.

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 three short sentences with no filler. The main action is front-loaded, followed by necessary target prerequisites and a useful operational note about tabs. Every sentence earns its place.

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 tool with only three parameters and an output schema, the description covers the core invocation context: the source, the target requirements, and the fact that no tab context is needed. The main gap is the lack of explicit failure/response semantics, which prevents a perfect score, but the essential information for a correct call is present.

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?

Schema description coverage is 0%, so the description must compensate. It implicitly maps extension_id to the target extension and message_json to the JSON message payload, but it leaves session_id entirely unexplained and does not clarify the expected JSON string format or any encoding requirements.

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 action ('Send a JSON message') with a precise resource ('from the BTAP extension service worker to another installed extension'). This clearly distinguishes call_extension from sibling tools such as list_extensions or set_extension_enabled, which manage extensions rather than message them.

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?

The description gives clear usage context: the target must be enabled and must declare the BTAP extension in externally_connectable, and the tool works without any tabs open. It does not name explicit alternatives, but there is no closely competing sibling tool for sending extension-to-extension messages, so the practical usage boundary is clear.

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