Prepare a call (preview, no call placed)

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

Beyond the annotations, the description discloses real behavioral traits: it validates and blocks emergency/premium numbers, auto-selects or confirms language, builds script and AI-agent instructions, creates a previewId resource while placing no call, and adds a provider-specific caveat about passing translatedScript for Twilio in non-English languages. This is unusually rich side-effect and constraint disclosure. No contradiction with readOnlyHint=false (a previewId is created) or destructiveHint=false.

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?

Three tight sentences, front-loaded with the sequencing and no-call constraint before the return-value detail and the Twilio caveat. 'No call is placed' slightly duplicates the title's 'preview, no call placed', a minor redundancy in an otherwise dense, well-ordered description.

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?

With 15 parameters, 0% schema coverage and no output schema, the description does describe the return payload (number, language, goal, script, cost, previewId), which removes the need to explain returns elsewhere. However, it leaves the majority of input parameters undocumented, so an agent must guess at provider, maxMinutes, keyPoints, questions, mustNot and several others.

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% across 15 parameters, so the description carries the full burden and largely fails: only translatedScript gets a real explanation (Twilio + non-English), while to, goal, callerName, provider, language, maxMinutes, mustNot, keyPoints, questions, record, context, onBehalfOf, sampleText and calleeTimezone are never clarified. The mention of 'script, cost, number, language' partly overlaps parameter names but adds no semantics.

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 names a specific verb and resource ('prepare' produces a preview, no call placed) and explicitly positions itself as 'Step 1 of 2', which cleanly separates it from place_call in the sibling list. It also lists the concrete outputs (number, language, goal, script, cost, previewId), so an agent can tell exactly what this tool produces versus its siblings.

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?

'Step 1 of 2' plus 'No call is placed' effectively signals when to use this instead of place_call, giving a clear sequencing rule. There is no explicit naming of the alternative tool, and the overlap with the estimate_cost sibling (which also estimates cost) is never addressed, so it falls short of a full when/when-not/alternatives statement.

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