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

Annotations already declare readOnly, idempotent, openWorld and non-destructive, so the safety profile is covered. The description adds real value beyond them by disclosing the inclusion/exclusion scope and the unit/address-type breakdown of the result. It stops short of describing auth or any edge cases, so a 4 rather than a 5.

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 sentences, no filler. The positive scope is front-loaded and the exclusions/routing follow immediately, so every clause earns its place.

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 parameterless read tool with no output schema, the description covers purpose, scope, excluded asset classes, sibling routing, and the shape/units of the return (per-address-type, BTC and sats). Nothing an agent needs to call it correctly 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?

Zero parameters, so there is no per-parameter semantics to document; the baseline of 4 applies. The description does not need to compensate for anything and the empty schema is consistent with the description.

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 native BTC balances') plus the exact scope (taproot P2TR and nested segwit P2WPKH, in BTC and sats). It also names the sibling tools it is not, so an agent can distinguish it from getRuneBalances/getXCPBalances 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?

Explicitly states what the tool excludes (runes, ordinals/inscriptions, Counterparty) and routes the agent to the named alternative for each case. This is a textbook when-not/alternatives clause, leaving nothing to inference.

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