JSONPlaceholder MCP Server

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

With no annotations provided, the description carries the full burden of behavioral disclosure. It states the tool retrieves data, implying it's a read operation, but doesn't disclose important behavioral traits like whether it requires authentication, has rate limits, returns paginated results, or what happens when an invalid ID is provided. For a tool with zero annotation coverage, this leaves significant gaps in understanding its behavior.

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 appropriately concise with a single sentence that efficiently communicates the core functionality. It's front-loaded with the main purpose and doesn't contain unnecessary words or redundant information. However, it could be slightly more structured by explicitly separating the two use cases (all posts vs. specific post).

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 moderate complexity (retrieval with optional filtering), lack of annotations, no output schema, and minimal parameter documentation, the description is incomplete. It doesn't explain what the return format looks like, error conditions, or how to handle the optional parameter. For a tool that could return either a list or single item, more context is needed for proper usage.

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 description mentions retrieving 'a specific post by ID', which corresponds to the 'post_id' parameter in the schema. However, with 0% schema description coverage and only one parameter, the description doesn't adequately explain parameter semantics. It doesn't clarify what happens when 'post_id' is null (retrieving all posts) versus provided, or the format/constraints of the ID. The description adds minimal value beyond the bare schema.

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: 'Retrieve all posts or a specific post by ID from JSONPlaceholder'. It specifies the verb ('retrieve'), resource ('posts'), and scope ('all' or 'by ID'), making it easy to understand what the tool does. However, it doesn't explicitly differentiate from sibling tools like 'search_posts' or 'create_post', which prevents a perfect score.

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 minimal guidance on when to use this tool. It mentions retrieving 'all posts or a specific post by ID', but doesn't clarify when to use it versus alternatives like 'search_posts' (for filtering) or 'create_post' (for adding posts). There's no explicit when/when-not guidance or mention of prerequisites, leaving usage context largely implied.

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