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

Annotations already declare readOnlyHint, idempotentHint, and destructiveHint=false, so safety is covered structurally. The description adds real behavioral value beyond that: it preserves exact integer/decimal/fraction inputs and returns source-to-result position mappings, which is useful given there is no output schema.

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?

Three tight sentences with the core operation front-loaded and no filler. The third sentence is a bit long but each clause (type preservation, return shape) carries distinct information.

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 simple one-parameter, read-only tool with no output schema, the description covers operation, accepted shapes, input-type preservation, and the return structure including position mappings. Nothing an agent needs in order to call it correctly appears to be 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?

With a single parameter at 100% schema description coverage, the schema already documents 'matrix' fully, so the baseline is 3. The description adds only 'rectangular or square', a minor hint that non-square inputs are accepted, but no format or element-typing detail beyond the schema.

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 gives a specific verb+resource ('Transpose ... matrix') and clarifies the mechanism ('exchanging rows and columns'), which unambiguously separates it from siblings like matrix_add or matrix_multiply. It does not name a sibling or a disambiguation condition, so it falls short of the top tier.

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?

'Useful for requests to show where each result entry originated' is an implied usage context rather than explicit when/when-not guidance. No alternative tool or prerequisite is mentioned, leaving the agent to infer selection from the operation name.

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