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

Annotations already mark readOnlyHint=true and destructiveHint=false, and the description reinforces a non-mutating lookup. It adds behavior not in annotations: id case/punctuation folding with examples, and that the id namespace is shared with feng shui/I Ching endpoints. This is useful operational context without contradicting the annotations.

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, both meaningful: the first itemizes what the lookup returns, the second gives id-normalization behavior and namespace consistency. Information is front-loaded and there is no filler. Minor opacity in 'what the chapter places there' keeps it from a top score.

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 read-only single-id lookup with three well-schema'd params and no output schema, the description covers what is returned and key invocation quirks. It does not describe the response shape, but the absence of an output schema is mitigated by listing the content categories. The invocable details (enums, lang fallback, compact) are already in the schema, so nothing critical 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%, so the baseline is 3; the schema already documents id, lang, and compact in detail. The description repeats the id folding already in the schema but adds the cross-endpoint id-space consistency. No further parameter explanation is necessary.

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 and resource ('Look up one Vastu direction') and itemizes the returned content: dikpala, mandala squares and devatas, chapter placement, and standing water meaning. The word 'one' plus the id suffix distinguishes it from the plural list endpoint get_vastu_directions. No ambiguity about what it does.

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?

It clearly conveys single-entry lookup ('one direction'), which implies use when a specific direction's details are needed rather than a list. It does not explicitly name get_vastu_directions as the alternative or state when-not-to-use, so it falls short of the strongest guidance. The shared-id-space note helps an agent know it is consistent with feng shui and I Ching endpoints, but is not a full routing rule.

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