mfp_update_fast

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

The description reveals the PATCH full-replacement behavior, the limitation that fasts cannot be listed, and the id sourcing constraint, all of which go beyond the annotations' idempotentHint and destructiveHint. This adds valuable context about the underlying API.

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 organized into concise paragraphs with an Args/Returns block. It front-loads the main purpose and uses bullets-like structure. The Args line mildly duplicates schema but is not excessive. Overall efficient.

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 small parameter count, rich schema, and annotations, the description covers purpose, usage constraints, id sourcing, and return value. It is complete enough for an agent to invoke correctly without needing additional context.

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 id, fast_started, fast_ended, and response_format. The description adds critical cross-parameter semantics: both time fields must be supplied even if only one changes, and id must come from a prior log call. While it doesn't repeat schema details, the PATCH behavior is essential for correct invocation.

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 opens with 'Update an existing fasting entry's start and end times', a specific verb+resource statement. It clearly distinguishes from siblings like mfp_log_fast (create) and mfp_delete_fast (delete) by focusing on updating times.

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?

It explicitly states that both time fields must be supplied due to PATCH full replacement, and explains that the id cannot be discovered via the MCP since no read endpoint exists; it must come from a prior mfp_log_fast call or the app. This is clear contextual guidance, though it doesn't explicitly name alternatives for creation/deletion.

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