Estimate call cost

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

Annotations already cover readOnlyHint and openWorldHint, so the bar is lower, yet the description adds real value: it names the data source (Twilio Pricing API), notes it is free and uses your credentials, and explains Bland is priced from a configured per-minute rate. It stays consistent with readOnlyHint rather than contradicting it, though it omits edge behavior such as missing credentials.

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?

A single tightly-packed sentence, front-loaded with the verb and resource, using a colon to enumerate the two provider paths and closing with the most important constraint. No filler; every clause carries information.

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 tool with no output schema and 0% parameter coverage, the description adequately explains provider mechanics and safety but leaves the two required parameters and the exact returned value unaddressed. An agent knows the intent but must infer the meaning of its inputs.

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 carries the burden, and it only partially compensates: the provider enum values (Twilio vs Bland) are explained and their pricing mechanisms distinguished, but "to" (destination identifier) and "minutes" (its 1-60 range and relationship to the estimate) are never clarified.

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 ("Estimate the maximum cost of a call") and immediately distinguishes itself from the call-executing siblings via "Never places a call," which separates it from place_call. An agent can tell what it does and what it does not do without opening the schema.

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?

The closing clause "Never places a call" implies the intended use case (check cost before/without dialing), but the description never explicitly says when to prefer this over place_call or prepare_call. Usage is inferable rather than stated, and no alternatives or exclusions are named directly.

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