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

Annotations already declare readOnlyHint, idempotentHint, and openWorldHint, so the safety profile is covered structurally. The description adds genuinely useful non-annotation context: 'Everything is handled in memory; no files are stored,' which explains why a tool named 'zip_files' is legitimately read-only and tells the agent there are no filesystem side effects. It stops short of mentioning size/count limits or failure behavior, but with annotations present the bar is lower.

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 tightly written sentences with no filler, and the operative capability is front-loaded before the caveat. The in-memory note is placed last where it belongs as a qualifier rather than leading. Nothing is redundant with 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?

An output schema exists, so return values need not be described, and the in-memory behavior plus both operating directions are covered. One gap: the description promises 'list ... the contents' as a capability, but the mode enum only exposes zip/unzip, leaving the agent unsure how listing is triggered. The 200-file cap is also only in the schema. Overall complete enough for correct invocation.

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 67%, so the schema already carries most of the burden, and the base64 encoding details for files[].data and archive.data live there. The description maps loosely onto the parameters ('from files' → files, 'contents of an archive' → archive) but adds no format, size, or mode-selection detail beyond what the schema states. 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?

The description names two concrete verbs (create, extract/list) against a single well-defined resource (ZIP archive), covering both directions of the operation. This is not confusable with compression siblings like compress_image or compress_pdf, which act on specific formats rather than producing an archive. An agent knows exactly what this tool produces without opening the schema.

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 two operating modes (zip vs unzip) are implied by the description and formalized in the mode enum, so usage is reasonably inferable. However, there is no explicit when-to-use/when-not guidance and no mention of the natural alternatives (compress_image, compress_pdf, images_to_pdf) for related file-bundling tasks. Guidance is implied rather than stated.

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