coord_describe

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

Annotations already declare readOnlyHint, idempotentHint, and non-destructive behavior, so the description doesn't need to repeat that. It adds value by explaining that the tool normalizes input and returns an explanation for invalid input, which is useful context beyond the safety hints. However, it doesn't describe the exact output structure or the precision levels returned, but given annotations cover safety, a 3 is reasonable.

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 description is well-structured, starting with the primary purpose, then explaining the normalization and precision implications, and ending with error behavior. Each sentence serves a purpose, and the use of a concrete example (4-digit grid reference, 5-char geohash) makes it informative without being verbose.

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?

With an output schema present, the description doesn't need to detail return values. It covers the tool's validation purpose, normalization behavior, and precision implications, which is sufficient for a single-parameter tool. A minor gap is not describing the exact output format, but that's covered by the output schema.

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 coverage is 100% (the only parameter 'value' is described as 'The coordinate string to inspect.'). The description adds context about what the tool does with the value, but doesn't add new parameter-specific semantics beyond what the schema already provides. Hence baseline 3.

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 clearly states it checks if a string is a valid coordinate and reports its precision. It specifies the resource (coordinate strings) and the operation (validate, normalize, state precision), distinguishing it from sibling tools that convert, transform, or measure.

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 explicitly mentions it is safe to use for validating user input before acting on it, and explains error behavior (returns is_valid=false rather than failing). This gives clear guidance on when to use it versus other tools, though it doesn't name alternatives explicitly, the context is clear enough.

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