Call the engineer

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

Beyond the annotations, the description discloses real-world side effects: the call costs money and interrupts a person. It also reveals the blocking behavior and that the return value is the engineer's spoken decision as JSON. Since annotations do not convey these consequences, the description carries that burden fully and successfully.

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 compact and every sentence earns its place: action, blocking behavior, triggering conditions, forbidden uses, real-world cost, and return format. It is front-loaded with the essential action and then gives decision criteria. No filler or redundancy.

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 high-stakes tool with 6 parameters and no output schema, the description still covers the essential operational context: when it is appropriate, what it does, what the user experience is, and what it returns. The input schema covers parameter mechanics, and the description covers real-world consequences and guardrails completely enough for safe invocation.

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 coverage is 100%, but the description still adds important semantic guidance beyond parameter names: context is read aloud so must avoid paths/hashes/code, options must be short enough to speak, default should never be set for destructive actions, and omitting default halts and waits. This is exactly the kind of usage nuance an agent needs to invoke the tool correctly.

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 opens with a specific verb and resource: 'Place a real phone call to the engineer who owns this session and block until they answer.' This makes the tool's core function unmistakable and distinguishes it from generic messaging or async notification tools. The title and description align without relying on the tool name alone.

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 states when to use the tool ('only when you are blocked on a decision that they must make') and gives concrete examples like ambiguous spec, destructive action, failing migration, and spending money. It also names the negative case: 'Never for lint, style, or anything you can decide from the code.' This is unusually clear routing guidance.

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