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

The description goes beyond the annotations (readOnlyHint=false, destructiveHint=false) by disclosing two meaningful behaviors: a name clash is refused unless replace, and an archive holding unsafe entries is refused rather than rewritten. These are concrete, actionable details. It does not contradict the annotation hints.

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?

The description is exactly two sentences, front-loading the primary action and then stating the key behavioral caveats. There is no filler or redundant restatement of the title.

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?

Given full schema coverage, absence of an output schema, and a moderate parameter count, the description captures the core use, the file-placement modes, and the two important refusal behaviors. An agent can decide when to call and what to expect on basic conflicts, though it stops short of explaining success return values or what 'unsafe entries' means exactly.

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?

The input schema fully describes all 6 parameters, so the baseline is 3. The description reinforces the meaning of paths and prefix ('under their own names, or under prefix') and the replace rule ('name clash is refused unless replace'), but it adds no parameter-level detail beyond what the schema already provides.

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 names a specific verb and resource: add files to an existing archive. The phrase 'existing archive' clearly distinguishes it from sibling tools like zip_create, and the mention of 'under their own names, or under prefix' captures the core operation.

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?

The description clearly establishes the context — adding to an existing archive — which implies when to use it versus creation, extraction, or listing tools. It does not explicitly name an alternative or state when not to use it, so it only falls short of full exclusion guidance.

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