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

Annotations already declare readOnly, idempotent and closed-world, so the safety profile is covered. The description adds genuine behavioral context beyond that: it explains that output is a formula string whose shape depends on mode, and enumerates the concrete tie-handling outputs (1,2,2,4 vs 1,2,2,3 vs 1,2.5,2.5,4 vs 1,2,3,4), which the agent could not infer from 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?

A single tight paragraph that front-loads the core purpose and then packs tie examples and mode semantics without filler. Slightly dense as a wall of parenthetical options, but every clause carries 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?

The tool's job is to emit a formula string and the description makes that clear, so the absence of an output schema is not a problem. Range format quirks are left to the schema's own description, which is acceptable, though a note on what the returned string looks like would have closed the last gap.

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 67% schema coverage, the description meaningfully supplements the schema: it defines the semantics of ties with worked sequences, explains what each mode produces, and clarifies that group causes ranks to restart per group. The only gap is direction/separator, which the schema already documents.

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?

Opens with a specific verb+resource: "Build a formula that ranks one column," which is unambiguous and distinct from the sibling filter/unique formula builders. It never explicitly names how it differs from sheets_filter_formula or sheets_unique_formula, so it stops short of the top mark.

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?

Usage is only implied through the mode explanation ("column fills the whole column from one cell; row is a per-row formula to drag down"), which helps pick a mode but is parameter guidance rather than when-to-use-this-tool guidance. There is no statement of when to choose this over the sibling formula tools or any preconditions on the range.

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