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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive), so the bar is lower; the description still adds that prices are current/volatile and that an empty result must be reported rather than fabricated. It does not discuss pagination or failure modes, but for a read-only listing this is solid added context.

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?

Two compact sentences with the core listing purpose front-loaded, followed by the mandatory pre-pay_bill sequencing. Every clause carries actionable instruction and there is no filler.

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?

There is no output schema, and the description fills that gap by saying what comes back (exact codes and current prices) and what to do when nothing usable returns. Enough for an agent to invoke and consume the result correctly.

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%, so the baseline is 3; the description goes beyond it by tying the returned codes to the variation_code argument of pay_bill, which is not derivable from this schema alone. The service/provider formats are already documented in the schema, so the added semantics come mainly from that cross-tool linkage.

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 (list) and resource (plans) scoped to three named services, and clarifies it returns exact codes and current prices. It is clearly distinguishable from siblings like list_international_options, list_schedules, and pay_bill, which share the 'list/pay' vocabulary.

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 to ALWAYS call this before pay_bill for DATA/CABLE/EDUCATION and to pass one of the returned codes as variation_code, plus notes that electricity and airtime have no plan list. This gives both the when-to-use trigger and the downstream call pattern.

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