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

Annotations already declare read-only, idempotent, non-destructive. Description adds valuable context: column union behavior, blanks for missing columns, row-count verification, and the failure mode it prevents. No contradiction.

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?

Four sentences, each packed with purpose, behavior, and usage. No filler, front-loaded with the main action.

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 merge tool with output schema and comprehensive annotations, the description fully covers behavior, edge cases, and usage scenarios. Includes row-count verification, making the output trustworthiness explicit.

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 covers both parameters with descriptions (100% coverage). Description adds the 'up to 20' limit and implies either urls or texts can be used, providing extra constraint context. Baseline 3 elevated to 4 for this addition.

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?

Clearly states it combines up to 20 CSVs into a single table, with specific details about column unioning and row-count verification. Distinguishes from sibling tools like diff_tables by focusing on merging rather than comparison.

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?

Provides explicit use cases ('monthly exports, per-store sheets, or any set of files with the same subject but drifting headers'). Lacks explicit exclusions or named alternatives, so not a 5, but clear context is given.

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