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

Annotations cover the safety profile, but the description adds genuinely new operational context: rate limit of 60 calls/minute per IP, no authentication required, data refreshed at most once per business day, and a documented error condition for short series. It also sets a communication obligation ('not a forecast or advice: say so when you quote it'), which no structured field conveys.

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 capability and outputs before usage, prerequisites and caveats. Dense and mostly waste-free, though some clauses ('Read-only, no side effects, no authentication') restate what annotations already declare.

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?

Despite an output schema being present, the description usefully characterizes the returned content, and it covers the prerequisites, error behavior and freshness constraints an agent needs before calling. Nothing material for correct invocation 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?

Schema description coverage is 100% and both parameters are documented in the schema, including the horizon default/units and the example key format, so the baseline is 3. The description only reinforces key provenance ('Needs a key from search_series') without adding new syntax or unit detail for horizon.

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 ('Project a series forward') and immediately enumerates the output the tool produces (point values, 80%/95% bands, combined ETS/ARIMA/Theta models, backtest errors, REM median). It explicitly distinguishes itself from the sibling get_series, so an agent can route without opening either 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?

Gives explicit when-to-use ('what's next' questions about inflation, exchange rates, interest rates or reserves) and names the alternative for the opposite case ('use get_series for past values'). It also states the prerequisite ('Needs a key from search_series') and the failure condition (too little history returns an error).

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