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

With no annotations, the description carries the full burden, and it does disclose real behavior: requests are scoped to a tab's cookie jar, output is streamed and written atomically, and no Save dialog appears. It is silent on failure/partial-write behavior, permission or auth requirements, and concurrency, which matters for a mutating filesystem operation.

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 tight clauses with zero filler and the key constraints front-loaded. The telegraphic, semi-sentence style trades some readability for density, but every phrase carries load.

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 7-parameter write-to-disk tool with no annotations and no output schema, the description covers the core semantics and the hard limitations but omits error behavior, overwrite/directory-creation consequences, and size-limit behavior. Adequate but with visible gaps.

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 57%, with mkdir, max_bytes, and overwrite carrying no description anywhere. The description's "cookie-scoped" and "no implicit tab selection" framing adds meaning to tab_id and url beyond the schema, but it says nothing about the undocumented three parameters, so it only partially compensates for the gap.

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 concrete mechanism (cookie-scoped HTTP GET streaming to an atomic file write), which is clearly distinct from browser-rendering siblings like goto or screenshot. It never explicitly contrasts itself with those siblings, so an agent has to infer that this is the file-retrieval path rather than rendering, but the purpose itself is specific and non-tautological.

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 POST/blob/challenge fallback" gives explicit negative conditions (don't use for POST endpoints, blob URLs, or challenge-protected resources), which is genuinely useful routing information. However, it names no positive trigger and no alternative tool to use for the excluded cases, so the when-to-use guidance is only half complete.

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