Explain the subscription lifecycle

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

Annotations already declare readOnlyHint, idempotentHint, and destructiveHint. The description adds 'Read-only, offline, deterministic,' which provides extra context beyond annotations (offline and deterministic are not captured by hints). It also describes the behavioral structure (failed preconditions return error codes). No contradictions.

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?

The description is well-structured: primary purpose first, then usage guidance, alternatives, and behavior notes. It is slightly verbose due to enumerating all nine operations, but every sentence contributes unique value. The layout is logical and front-loaded.

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 complex tool returning a state machine, the description covers what is returned, when to use it, alternatives, parameter behavior, and characteristics. The presence of an output schema means return values need not be detailed. Comprehensive for the task.

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% for the single `operation` parameter, and the schema description already states that omission returns every operation. The description repeats this guidance ('Omit `operation` for the whole machine') without adding new semantic information, so it stays at the baseline.

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 clearly states the tool returns the subscription lifecycle state machine, enumerates the operations covered, and specifies the exact output components (legal states, fields to read, scenarios, error codes). It distinguishes itself from siblings like pc_get_scenario and pc_plan_subscription_change by positioning itself as the 'what can I do right now' reference.

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 explicitly states when to use this tool ('before reaching for an endpoint') and names specific alternatives with their use cases: 'For the endpoint itself use pc_get_scenario, for an ordered call sequence use pc_plan_subscription_change, and to decode a rejection use pc_lookup_error.' This is explicit when/when-not guidance.

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