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

Annotations already establish readOnly/non-destructive/non-open-world, so the bar is lower, and the description still adds real behavior: the result is rendered as a card and the call is free (no quota cost). It also imposes a disclosure constraint on the agent's phrasing ('call it usage balance', don't discuss tokens), which is behavior beyond the schema and annotations.

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?

Four short sentences with the purpose front-loaded, then cost, then trigger conditions, then phrasing rules. Every sentence carries information; only the phrasing-policy sentence is slightly tangential to invocation, but it still earns its place as an output-handling rule.

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 convey what comes back, and 'plan and remaining usage balance (shown as a card)' does that at a high level appropriate for a single-parameter read tool. Fields within the card and renewal-data specifics are left unspecified, which is the remaining gap.

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?

There is a single optional parameter with 100% schema description coverage, including an enum of ar/en and an explanation that it should match the user's writing language. The description adds nothing about the parameter, so the baseline of 3 applies — the schema carries this dimension entirely.

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 opens with a specific verb and resource: 'Show the user's Go Shift plan and remaining usage balance.' That resource is unique among a sibling list dominated by ad-platform and reporting tools, so an agent can tell this is the account/plan query rather than a budget or performance tool 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?

It gives explicit triggers — 'when the user asks about their plan, balance, limits or renewal' — which covers the realistic intents well. It does not name a when-not case or point to an alternative sibling (e.g. budget_status), which is the only thing separating it from a 5.

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