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

Annotations already declare readOnlyHint=true and destructiveHint=false, so the safety profile is covered. The description adds context about what the call returns and flags that the element/planet/sign depends on 'the requested reading', which is a useful behavioral link to the letterAttribution parameter. It does not go deeper into response shape or edge behavior, but for a read-only getter with a thorough schema this is adequate.

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 sentences with no wasted words: the first front-loads the action and enumerates the return fields, which is justified because there is no output schema; the second states the use case and contrasts with the all-22 call. The first sentence is dense, but every item in it adds agent-usable information about the response payload.

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 tool with 4 parameters, 100% schema coverage, and a readOnly annotation, the description fills the main gap — the absence of an output schema — by enumerating every return field. Combined with the schema, an agent knows what to pass, what to expect back, and when to prefer this over the multi-letter endpoint. The only minor omission is a description of the JSON response envelope, which is not critical for a single-letter detail call.

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 all four parameters (id enum with 22 values, lang, compact, letterAttribution) are documented inside the schema itself, putting the baseline at 3. The description's only param-adjacent contribution is 'under the requested reading', which reinforces the letterAttribution dependency without adding enum-level detail. No gap to penalize.

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 a specific verb-resource pair ('Return one Hebrew letter in full') and enumerates exactly what comes back: glyph and final form, both gematria readings, Sefer Yetzirah class and meaning, element/planet/sign, tarot trump, and path number. It also carves out its niche against the all-22 helper by stating 'one row rather than all 22 letters', which distinguishes it from sibling get_kabbalah_letters.

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?

The second sentence names the target context ('Built for letter detail pages') and the audience ('any reader who wants one row rather than all 22 letters'), giving a clear when-to-use signal and an implied exclusion of the full-list sibling. It does not name that alternative explicitly or lay out selection logic among the letter-family endpoints, so it stops just short of the explicit when/when-not bar.

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