Replace matching text in a file.

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

Annotations already indicate destructive behavior. The description adds the constraint that old_str must appear exactly once, which is critical behavioral context beyond the annotations. However, it does not disclose error handling or side effects.

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 two short sentences with no wasted words. It front-loads the action and then provides constraints concisely.

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?

The tool is simple with 3 required parameters and an output schema. The description covers the main behavior but omits details on error conditions (e.g., if old_str not found or appears multiple times). Still adequate for a straightforward 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 0% schema coverage, the description carries the burden. It explains the roles of old_str and new_str but lacks detail on expected formats, encoding, or behavior if constraints are violated. It provides minimal but sufficient meaning.

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 clearly states the action (replace), the resource (file), and constraints (exact occurrence, once). It distinguishes from siblings like write_file and edit_file_lines by specifying content-based matching without line numbers.

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 provides clear context for when to use the tool (replace a unique string) but does not explicitly state when not to use it or mention alternatives beyond implicit differentiation from sibling names.

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