Synastry

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

Annotations already declare readOnly, idempotent, non-destructive, so the safety profile is covered. The description adds meaningful context beyond that: degraded output when timeUnknown is set (null houses, angles, sect) and a concrete cost of 50 credits (Tier 3), which an agent needs for call budgeting.

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 front-loaded sentences carry purpose and the key edge case, followed by compact bracketed metadata (group, endpoint, required, cost). No filler, though the metadata lines are somewhat boilerplate.

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?

An output schema exists so return values need no explanation, and the schema itself fully documents the two nested parameters. The description adds the one behavioral caveat (timeUnknown degradation) and cost, leaving nothing an agent needs to invoke correctly 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 chart1/chart2 are thoroughly documented, including a nearly identical timeUnknown explanation on each nested object. The description largely restates that nested-object text, so it adds little beyond the schema; baseline 3 is appropriate.

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: calculating cross-chart aspects between two natal charts, scoped to relationship analysis. An agent can tell it apart from non-relational chart tools, though it never distinguishes itself from the many other relational siblings (composite, davison, synastry_aspect_grid, match_score).

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 one concrete usage rule (either partner may set timeUnknown and still get cross-aspects), which is real guidance. But there is no statement of when to prefer this over sibling relational tools such as astroway_relational_composite, astroway_relational_match_score, or astroway_relational_synastry_aspect_grid — usage is only implied by 'relationship analysis'.

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