FastMCP Development Assistant

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

Annotations already declare readOnlyHint=true and openWorldHint=true, indicating this is a safe read operation that may access external resources. The description adds valuable context beyond annotations by specifying the two sources it fetches from (main package vs @types/ packages) and the search behavior. This provides practical implementation details that help the agent understand how the tool works, though it doesn't mention rate limits or authentication needs.

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 extremely concise with just two sentences that directly state the tool's purpose and approach. Every word earns its place - the first sentence establishes the core functionality, the second explains the sourcing strategy. No wasted words or redundant information.

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 read-only tool with good annotations (readOnlyHint, openWorldHint) and 100% schema coverage, the description provides adequate context. It explains what the tool does and where it sources from. The main gap is the lack of output schema, so the description doesn't clarify what format the type definitions are returned in (e.g., file paths, raw content, structured data). However, given the annotations cover safety and external access, and the schema documents parameters well, it's reasonably complete.

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 100%, with all parameters well-documented in the schema. The description doesn't add any parameter-specific information beyond what's already in the schema descriptions. It mentions the general approach (fetching from main or @types packages) which relates to the searchMode parameter, but doesn't provide additional semantic context. Baseline 3 is appropriate when schema does the heavy lifting.

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 tool's purpose: '指定されたNPMパッケージのTypeScript型定義を取得します' (fetches TypeScript type definitions for specified NPM packages). It specifies both the action ('取得します' - fetches) and resource ('TypeScript型定義' - TypeScript type definitions), and distinguishes from siblings by focusing specifically on type definitions rather than package analysis, documentation, or cache statistics.

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 implied usage context by mentioning it fetches from 'メインパッケージの型定義または@types/パッケージ' (main package type definitions or @types/ packages), which suggests when different sources might be used. However, it doesn't explicitly state when to use this tool versus alternatives like 'analyze-npm-types' or provide clear exclusions. The guidance is present but not explicit.

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