fable_files

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

No annotations are provided, so the description carries the full burden. It discloses that the tool lists files with 'edit/write counts and last-touched time,' implying a read-only, non-destructive operation. However, it does not discuss performance, authorization needs, or other behavioral traits beyond the basic functionality.

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 concise (three sentences) and front-loaded with the primary action. Every sentence adds value: purpose, return info, and usage guidance. No redundant or verbose language.

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 3 simple parameters and no output schema, the description fully covers the tool's functionality, return values, filtering options, and intended use case. It is complete for an agent to understand when and how to use the tool.

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?

With 67% schema description coverage (query and session_id described in schema, limit not), the description adds value by explaining that the parameters are for filtering ('Filter by a path substring or a session id'). It reinforces the purpose of the parameters beyond the schema descriptions.

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 uses specific verbs ('List'), identifies the resource ('files Claude has edited'), and clarifies scope ('across the whole archive, or within one session'). It also distinguishes from sibling tool fable_file_history by indicating when to use this tool before pulling history.

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 explicitly states the primary use case: 'Use to DISCOVER what a past session changed before pulling a file's history.' It also explains filtering by path substring or session id, providing clear context for when to use this tool, though it doesn't explicitly state alternatives or when not to use.

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