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

Annotations already declare readOnly/idempotent/non-destructive, yet the description adds material context beyond them: lines:manage permission requirement, per-account rate limiting, confidentiality behavior (callers masked to last four digits), and what is absent (no pause/edit/close). This is exactly the added-value layer annotations cannot express.

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 the 'use it first' directive, then return fields, then escape hatches — a sensible order. It is a dense single paragraph with a long parenthetical on balance units and forwarding codes, but almost every clause carries decision-relevant information given there is no output schema.

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 no output schema, the description must document returns and does: status enum values, billing_mode, balance semantics per line type, forwarding start/stop codes per carrier, and the 10-call recent_calls cap with masking. Permission scope, idempotence and the absence of mutation tools are all covered, leaving no gap an agent would hit when calling it.

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?

The tool takes zero parameters, so there is nothing to disambiguate and the baseline applies. The description instead spends its words on return shape, which is the right trade-off; no parameter-level meaning is missing.

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 — listing the signed-in owner's own After Hours answering lines plus unpaid pending set-ups — and scopes it to the owner only. An agent can distinguish it immediately from get_line_calls, get_line_messages, get_answering_line_offer and set_up_answering_line.

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 "Use it first" and explains why: it yields the line_id that get_line_calls, get_line_messages, get_sip_address and buy_pack require. It also names the alternatives for the sub-resources and states outright that no pause/edit/close tool exists, routing that work to the owner console.

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