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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive), and the description goes well beyond them: a 90-day hard retention limit with the explicit instruction to 'say so instead of implying completeness', a 200-entry cap, newest-first ordering, and per-entry fields (action, timestamp, channel, from/to values). This is exactly the behavioral context an agent needs.

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 the core purpose, then detail, with the critical 'HARD LIMIT' constraint emphasized mid-text. It's on the denser side and repeats the action list already in the enum, but nearly every sentence carries operational value.

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 fully compensates by describing the return shape (entry fields, ordering, channel values, from/to for billing_cycles_count changes), the entry cap, and the retention window. Nothing needed to call or interpret the result is missing.

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%, and the schema already documents both `number` (full DID digits) and the `action` enum with all six values. The description largely restates the action list in prose and repeats the number's origin, adding little parameter meaning beyond what the schema provides, so the baseline 3 is appropriate.

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 ('Return the billing/lifecycle history of one DID') and enumerates exactly what the history contains, so an agent can distinguish it from get_did (current state) and list_dids (enumeration) without opening any 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?

It tells the agent where to get the required `number` (from list_dids / get_did) and clarifies that it returns history rather than current state, which routes usage implicitly. It stops short of explicitly naming an alternative for 'when not to use' or stating prerequisites, so it's clear context without exclusions.

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