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

Annotations give the safety profile (readOnlyHint=true, destructiveHint=false), and the description adds genuinely new context: the transaction is simulated against mainnet, returned unsigned, never executed, and the service is non-custodial and holds no keys. This explains why a 'deposit' is correctly flagged read-only rather than contradicting it. It stops short of describing constraints like slippage/expiry or the returned tx format.

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 core action and output type are front-loaded in the first two sentences. The tail clauses repeat the custody/unsigned message ('never sees or holds keys and never moves funds' vs. 'UNSIGNED transactions only') and the boilerplate 'Education only' line, which is slightly redundant but not wasteful enough to hurt.

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 build-transaction tool with no output schema, the description covers the essentials an agent needs: what it produces (unsigned bytes), that it is a mainnet simulation, and the non-custodial safety model. It omits what the caller must do with the bytes (sign/submit) and any assumption about the sender owning the BalanceManager, which would have made it complete.

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%, so all four parameters (sender, balance_manager_id, coin, amount) are already documented with formats and bounds. The description adds no additional parameter meaning beyond restating the coin source; baseline 3 applies when the schema does the heavy lifting.

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 ('Deposit a coin from your wallet into your own BalanceManager') with an explicit scope qualifier ('your own'), which cleanly separates it from the sibling build_bm_withdraw_tx. It also pins the output artifact ('Returns UNSIGNED tx bytes').

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?

Implied usage is clear: you deposit into a BalanceManager you already own, and the schema notes the id comes from build_create_balance_manager_tx effects. However, the description never names the alternative tools (e.g. build_bm_withdraw_tx for the reverse, build_create_balance_manager_tx as the prerequisite) or states when not to use it.

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