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

Annotations already cover the safety profile (readOnlyHint=false, destructiveHint=false, idempotentHint=false, openWorldHint=true), and the description adds a genuinely useful non-schema trait: the 250-credit Tier 5 cost and an explicit "confirm with user before invoking" caution. It also notes the computation (fast and slow planet transits within the month). It does not mention non-idempotency/repeat-cost, which would have pushed it higher.

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 purpose in the first clause, followed by a comparative scope note, an input list, and clearly demarcated group/cost metadata lines. Compact and well-ordered, with only the input enumeration bordering on restating the schema.

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 complex tool (8 params, nested chart object, output schema present), the description supplies purpose, scope, and cost without needing to explain return values. It is complete enough for correct selection and invocation, though it leaves the non-required compact-mode params (fields, precision) undocumented.

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 low (38%), so the description should compensate, but it only enumerates input names ("chart, year, month (1-12), language, tone, length") without adding meaning beyond the schema's own ranges and enums. It omits the two parameters not listed (fields, precision) and gives no format detail for chart or language/tone/length, so it adds little semantic value over the structured fields.

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 resource and output type ("Single-month forecast") and distinguishes its scope from a named sibling concept ("Tighter scope than year-ahead"), which lets an agent separate it from the year-ahead narrative without opening the schema. It stops short of routing against the other narrative siblings (natal, synastry, transit), so it is clear but not fully differentiated.

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?

"Tighter scope than year-ahead" implies when this tool is the right choice versus the year-ahead sibling, and the cost warning tells the agent to confirm before invoking. However there is no explicit when-not statement or routing among the many other narrative tools, so guidance is implied rather than spelled out.

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