ass_open

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

With no annotations, the description carries the burden and does reasonably well: it discloses two concrete failure modes (missing file raises ToolError; forced encoding that fails to decode raises ToolError) and explains doc_id as an optional registry id. It does not say whether loading mutates state on disk or how it interacts with existing open documents, which keeps it short of a 5.

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 first sentence is front-loaded and wastes nothing, and the Args list is tight. The Returns section enumerating every summary field is bulky and largely redundant given a declared output schema, which keeps it from a 5.

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 file-open tool with an output schema, annotations absent and 0% schema coverage, the description supplies purpose, all parameter semantics, error behavior, and even the 0-based line index convention. An agent has everything needed to call it correctly.

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 0% (only bare titles like 'Path'), so the description must compensate and it does: path is the file to open with an error condition, doc_id is an optional registry id, and encoding overrides the automatic sniff with a failure condition. All three parameters gain meaning absent from the schema.

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 (open) and resource (ASS/SSA file) plus the resulting effect: it becomes the current document. That effect distinguishes it from read-only siblings like ass_document_info and from ass_new_document, so an agent can tell what state change this causes 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?

Usage is implied by 'open a file and make it the current document', but the description never says when to prefer this over ass_new_document, ass_select_document, or ass_import_srt, nor does it state any exclusions. It is adequate for an obvious verb but leaves alternative selection to inference.

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