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

Annotations cover the safety profile (write, open-world, non-destructive). The description adds genuinely useful behavior beyond them: the payload is passed through with no shape validation, implying the server performs no transformation and that malformed payloads surface as Garmin-side errors.

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?

Short and front-loaded, but sentence two largely restates sentence one ('from a payload sent to Garmin verbatim' / 'Sends `payload` to Garmin verbatim'), a small redundancy in an otherwise tight definition.

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 write tool with no output schema and an open-world hint, the core passthrough semantics are present, but the description omits what the call returns, failure behavior when Garmin rejects the payload, and any pointer to the sibling structured tool or payload reference.

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?

One required parameter with 0% schema coverage, so the description must compensate. It explains how the value is handled ('sent verbatim, no shape validation') but gives no hint at the expected object shape, keys, or where to source them, leaving the agent to guess the structure.

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?

Specific verb+resource: 'Creates a manual activity from a payload.' The 'from_json / verbatim' framing communicates the distinguishing trait versus the sibling create_manual_activity (structured fields), but the description never names that sibling, so the agent must infer the split.

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?

Usage is only implied: the 'verbatim, no shape validation' phrasing suggests this is the raw-passthrough escape hatch used when you already have a complete Garmin-shaped payload. It never states when to prefer this over create_manual_activity, nor any prerequisites or exclusions.

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