mfp_update_fast

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

Annotations already indicate readOnlyHint=false (mutation), destructiveHint=false, and idempotentHint=true. The description adds substantive behavioral details: PATCH is a full replacement of both time fields, and the id sourcing constraint (no list endpoint). These go beyond the annotations and are critical for correct invocation, giving the agent a clear picture of the tool's inner workings.

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 succinct and well-organized. It leads with the purpose, then explains the PATCH behavior and id sourcing in separate concise paragraphs, followed by Args and Returns sections. Every sentence contributes essential information without redundancy. The structure makes it easy for an agent to parse and act on.

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 mutation tool with no read endpoint, the description covers all necessary context: what it does, an important behavioral caveat, how to obtain the required id, and the return value. Even without an output schema shown, the description mentions the return format. The tool is fully contextualized for an agent to invoke it correctly.

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 schema already provides descriptions for each property (id, fast_started, fast_ended, response_format). The description reinforces the key semantic: both fast_started and fast_ended are mandatory and must be supplied together due to PATCH replacement. It lists the parameter names but does not add per-field explanations beyond what the schema offers. However, the PATCH note significantly clarifies how to set the time parameters, so the description adds value.

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 action: 'Update an existing fasting entry's start and end times.' It specifies the verb, resource, and fields, and distinguishes it from sibling tools like mfp_log_fast (create) and mfp_delete_fast (delete). The purpose is unambiguous and immediately understood.

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 critical usage context: it explains that both time fields must be supplied due to PATCH's full-replacement semantics, and it notes the MCP cannot list fasts, so the id must come from a prior mfp_log_fast call or app capture. This informs when and how to use the tool, though it does not explicitly contrast with alternatives like mfp_delete_fast. Still, the guidance is practical and valuable.

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