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

Annotations already declare readOnlyHint=false and destructiveHint=false, so safety is partly covered. The description adds real value beyond them by disclosing the data consequence: columns are appended at the end and existing records are left empty (i.e., no backfill, no data loss). It omits the approval/needs_confirmation flow that the approvalId parameter implies.

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?

Two short sentences, zero filler, with the verb and resource front-loaded and the behavioral caveat placed second. Every sentence 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?

For a mutation tool with no output schema, the description covers purpose and one behavioral consequence, and the rich schema carries most remaining detail (limits of 30 columns, sheetId source, approval flow). It still leaves prerequisites and the approval handshake to inference, so it is only minimally complete.

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 description coverage is 80%, so the schema already documents sheetId, table, workspace, approvalId, and the nested column fields (name, type, format, options, description). The description adds no parameter-level detail beyond what the schema provides, so the baseline 3 applies.

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?

States a specific verb and resource ('Adds columns') plus scope ('to the end of a table'), which distinguishes it from napkin_tables_create and napkin_tables_add_records without naming them. Clear and unambiguous, but it never explicitly routes the agent away from the sibling tools that also mutate table structure.

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?

No when-to-use guidance: it doesn't say to reach for this only on an existing table, nor how it relates to napkin_tables_create (which likely defines columns up front) or napkin_tables_update_records. The agent must infer the scenario entirely from the tool name.

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