tf_cost_estimate

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

With no annotations, the description carries the burden. It discloses the skip condition when the API key is unset, which is useful, but does not state whether the operation has side effects, requires a prior plan, or what happens if the API key is missing (e.g., returns null vs error). The description is somewhat opaque about the operational details.

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 a single, efficient sentence that front-loads the primary action and outcome, with the conditional placed as a parenthetical. There is no wasted wording or redundancy.

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 the tool's simplicity (one parameter, no output schema), the description covers the core function and the key conditional, but omits the meaning of workspaceId and any prerequisite like requiring a successful tf_plan. This leaves the agent to guess how to invoke it correctly, warranting a middle score.

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?

The input schema has a single parameter (workspaceId) with 0% description coverage, and the tool description does not mention this parameter at all. The agent receives no meaning about what workspaceId is or how to fill it correctly, leaving a critical 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 clearly states the action ('Runs Infracost'), the target ('against the current plan'), and the output ('returns a monthly cost delta'). This distinguishes it from sibling tools that handle planning, approval, or apply phases, making its purpose unambiguous.

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 implicitly indicates it's for cost estimation after a plan exists, and mentions a conditional (skipped if INFRACOST_API_KEY unset), but does not explicitly say when to use it over alternatives like tf_plan or tf_apply. No explicit 'use this instead of X' guidance is provided.

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