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

Adds substantial context beyond the annotations: replacement semantics ('the value replaces the previous one'), ~15-minute propagation latency, explicit non-instant behavior, billing semantics ('counts as a billable metric update' with a billing error path), and the returned payload. This is exactly the operational detail an agent needs for a write 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 purpose and tightly organized: purpose, trigger, replacement/latency, alternative, prerequisites, billing, return. It runs long for a single paragraph, but nearly every sentence carries actionable information, so almost nothing is wasted.

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?

Given a write tool with an output schema, the description covers everything else an agent needs: prerequisites, latency expectations, an alternative for the urgency case, billing failure behavior, and confirmation that the updated metric is returned. No meaningful gap remains.

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 100%, so key, value, and timestamp are already well documented in the schema, including the number-vs-string value rules and the timestamp default. The description reinforces the key identification but adds no parsing or format detail beyond the schema, so baseline 3 applies.

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 precise verb and resource: 'Record the latest value of a Lock Screen Widget metric, identified by its key.' The framing (set/record a value, not create or update the metric itself) clearly distinguishes it from create_widget_metric and update_widget_metric.

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?

Explicitly says when to use it ('whenever the tracked number or text changes'), names the alternative for the immediate case ('for an immediate alert, use send_push_notification'), and points to prerequisites (list_widget_metrics, create_widget_metric). Both the trigger condition and the sibling routing are spelled out.

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