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

Annotations already declare readOnlyHint=true, idempotentHint=true, destructiveHint=false and openWorldHint=true, so the safety profile is covered. The description does add genuinely useful non-annotation behavior: omitting dates returns ~25 recent points rather than full history, and an unknown code and an empty range both surface as a named `no_data` error. It does not describe the shape of returned observations, but overall it adds real value beyond the 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?

Front-loaded with the core purpose, then codes, then the date-range behavior and error semantics. Dense but every sentence carries information; the parenthetical examples are slightly list-like but stay justified.

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 covers the default result size and the no-data error path, which are the main behavioral unknowns. It stops short of describing the fields in a returned observation, which is the one remaining gap for a data-retrieval tool.

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 the baseline is 3, and the description goes beyond the schema by explaining the default behavior when both date parameters are omitted and by supplying worked example codes. It does not explain the start/end mutual-requirement beyond what the schema already states.

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+resource: 'Historical observation series for a single SARB indicator, identified by its TimeseriesCode.' It also distinguishes itself from siblings by naming where codes come from (home_rates, current_market_rates, cpd_rates, exchange_rates) and pointing to sarb_policy_rate as an alternative for the policy rate.

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 tells the agent how to obtain a code, when to use sarb_policy_rate instead, and how to bound a range versus omitting dates for the default window. This is close to a decision tree, leaving little to inference.

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