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

Goes well beyond the readOnlyHint annotation by disclosing the calculation moment ('at noon UTC'), the accuracy provenance ('Verified against NASA JPL Horizons'), and the dynamic default behavior that keeps a published page current without redeployment. These are real behavioral traits an agent needs to decide when results are time-anchored and how inputs affect the response.

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?

The first three sentences carry dense, valuable information with front-loaded facts. The closing keyword-style sequence ('Monthly ephemeris API, tropical position table, daily planet transit positions, ecliptic longitude calculator') is largely redundant repetition of earlier content, though it also holds the useful JPL verification fact. It would average every sentence earns its place.

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-required-parameter tool with 100% schema coverage, the description fully conveys the body list, date range, temporal reference, return fields, and default-current behavior. The annotation already covers the safety profile, and the description covers the epistemic context; what an agent needs to invoke and interpret the call is present.

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 already documents all 4 parameters at 100% coverage, so the baseline is 3. The description adds practical value by explaining why omitting year and month yields the month-in-progress (a 'stay current without a redeploy' strategy), giving the agent a semantic reason to prefer defaults. That context is genuinely additive rather than a restatement.

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?

The description opens with the verb 'Get' and a precise resource: daily tropical ecliptic positions for an exact enumeration of 14 Western bodies across a full month. It names the specific outputs (longitude, zodiac sign, degree within sign, retrograde status), which separates it from sibling tools like post_astrology_transits_monthly (aspect-oriented) and post_astrology_planets (non-monthly position data).

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?

Use cases are explicit: 'Essential for ephemeris tables, transit tracking, retrograde calendars, and planetary movement charts.' It also gives actionable input guidance ('Omit year and month to get the month in progress, so a published ephemeris page stays current without a redeploy'). However, it stops short of naming sibling alternatives or stating when not to use it.

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