统计表行数

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

Beyond the readOnly/idempotent annotations, the description discloses that the default is exact COUNT(*), that exact=false reads an estimate that may be unavailable because most tables lack statistics, and that ALL_TABLES.NUM_ROWS is unreliable. This adds real behavioral context and does not contradict 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?

Three concise sentences: what it does, a critical caveat, and a usage tip. Every sentence carries necessary information and the main action is front-loaded.

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 row-count tool with a full schema and output schema, the description covers the essential caveats (NUM_ROWS unreliable, exact=false fallback) and points to the right sibling. Nothing needed to call it correctly 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 coverage is 100%, so the baseline is 3. The description adds value by explaining the practical consequence of exact=false in this database (statistics usually unavailable), which enriches the schema's parameter descriptions.

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 '返回一张表的行数' — a specific verb plus resource. It also distinguishes itself from dm_list_tables by warning that NUM_ROWS is usually NULL, so an agent can immediately tell this tool from its sibling.

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 instructs not to use dm_list_tables' NUM_ROWS as the real row count and to use this tool instead. It also gives usage guidance for large tables: set exact=false to use statistical estimates when available.

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