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

Annotations already declare readOnlyHint=true and openWorldHint=false, so the safety profile is clear. The description adds that this is a hypothetical lookup ('would credit') and mentions allowed amounts, but does not describe error behavior for unknown addresses or any auth requirements.

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 definition is a single efficient sentence with no wasted text. The key behavior is front-loaded, though the term 'Mailgi' is ambiguous and slightly undermines precision.

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?

The tool is simple and the description covers the core return concepts (wallet and allowed amounts). Still, without an output schema, it could say more about response shape or what happens if the address has no eligible wallet.

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 description coverage is 100% and the single address parameter is already documented as 'The agent's email or alias address.' The description's 'Mailgi address' adds little beyond the schema and contains a likely typo.

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 uses a specific verb ('Shows') and states the resource: which wallet a top-up would credit plus allowed amounts. It is clearly a read-only lookup, though it does not explicitly distinguish itself from siblings like topup_start or topup_status.

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?

Usage is implied: this is a pre-top-up lookup to see where funds would go and what amounts are permitted. However, the description never states when to use this versus topup_start, topup_status, or billing_topup, nor does it mention prerequisites such as authentication.

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