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

Annotations already carry readOnlyHint=true and destructiveHint=false, so the bar is lower, but the description adds substantial behavioral context: 'stat does not read the contents of JSON, Markdown, or other text files,' attach is for complete images only, --kind mcp selects MCP Spaces, up to 30 operations can be batched, and limits are routed to hf://README.md. No contradiction with annotations.

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 long, but the density is justified by six subcommands, arbitrary string arguments, scopes, and enums; the table-like grammar block and front-loaded 'When to use' section make it highly parseable. Minor redundancy: the Examples section and the separate Usage block both demonstrate ls calls, and the title overlaps the 'When to use' list.

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 high-complexity tool, the description covers command selection, search scopes, trending endpoints, paper-specific behavior, batching ('Issue one hf_fs call'), and flag minimization ('Omit --limit, --sort, and --type unless the request requires them'). Residual details are explicitly routed ('Limits and path-specific behavior are documented at hf://README.md'), and an output schema exists so return-value semantics need not be duplicated.

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% (the top-level operations property has no description), so the description must carry the full burden and does: it defines the complete grammar for all six commands with flags, enumerates TYPE and SORT values, specifies 'each string below is one args array item,' declares 'URI is a canonical hf:// URI,' and gives concrete invocation examples.

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 states a specific resource and mechanism: 'Use hf_fs for Hugging Face Hub filesystem operations,' preceded by a concrete 'When to use' list covering models, datasets, Spaces, papers, docs, and trending content. The six-command grammar (ls/cat/attach/stat/find/search) over canonical hf:// URIs makes it clearly distinguishable from siblings like hub_repo_search and hf_whoami even without naming them.

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?

Provides explicit subcommand selection rules: 'Use search for discovery, ls for a known directory, find for recursive matching within a known scope, stat for filesystem metadata or an uncertain target type, cat for text contents, and attach for a complete JPEG, PNG, or WebP image.' It also gives when-not guidance ('do not add ls or stat first' for exact text-file URIs) and hard constraints like 'Paper and documentation search require QUERY.'

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