write_char

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

With no annotations, the description takes on the full disclosure burden and does well: it reveals the arming precondition, that each call consumes one write from a budget, that firmware-update services are blocked, and how the write type is chosen by default. It does not say what happens when the budget is exhausted or the write is refused (error vs. partial result), which is the main remaining gap for a mutation 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?

Front-loaded with the action and return value, then precondition, then budget and default behavior. Dense and free of filler, though the fragmented line-broken style and the slightly opaque 'firmware-update services stay blocked' phrase cost it a point.

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?

An output schema exists, so the return needn't be described further; the description sensibly spends its words on authorization gating and write-mode defaults instead. The remaining shortfall is caller-facing: no error/refusal behavior and no input format guidance for the three required-but-undocumented parameters.

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 and only partly does: it explains `response` fully (null = auto, true = wait for ack, false = fire and forget). For `address`, `char_uuid`, and `data_hex` it only implies roles — no format guidance on MAC vs handle, full vs short UUID, or accepted hex string syntax and byte order.

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?

States a specific verb and resource ('write hex bytes to a characteristic') plus the return value ('returns the writes left'), which cleanly distinguishes it from read_char and subscribe among the siblings. An agent knows immediately this is a mutating BLE write, not a read or a subscription.

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?

Gives a hard precondition ('refused unless the human armed this device by running `harald arm <address>`') and an explicit usage rule for the response parameter (true when you need an acknowledgement, false when you don't). It also scopes out firmware-update services. It stops short of naming sibling alternatives, but the context is otherwise unambiguous.

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