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

Annotations already declare readOnlyHint=true, so the safety profile is covered. The description adds genuinely non-obvious behavior beyond that: planned future transactions are excluded from the calculation and the result is null rather than an error when no transactions exist — both are important for correct downstream handling.

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 plus a usage pointer, with the core behavior and edge case front-loaded and no redundant restatement of the name. Every sentence carries information an agent needs.

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 zero-parameter read-only helper, the description covers everything needed: what is returned, the format, the empty case, an exclusion rule, and a suggested use. No output schema exists, but the return value is fully described inline.

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?

The tool takes no parameters, so there is nothing to disambiguate and the baseline applies. The description correctly implies the scope is the whole account dataset with no filtering inputs.

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 ('Get the date of the first transaction on record'), specifies the return format (YYYY-MM-DD) and the null case, so an agent knows exactly what comes back. It is clearly distinct from sibling list/report tools such as get_transactions_summary or search_transactions.

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?

The final sentence gives an explicit use case: 'Use it to pick a start date for the report tools,' which is real routing guidance toward period-based siblings. It stops short of naming a specific alternative or stating when not to use it, so it is strong but not exhaustive.

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