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

Annotations already cover read-only, idempotent, and closed-world, but the description adds real context beyond them: "Nothing is stored" (no persistence side effects), no auth/account required, and a 5000-note listing cap plus a 1 MiB input ceiling. The gap is that it doesn't say what happens past 5000 notes—whether notes are truncated, how to page, or whether a summary count is returned.

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 returned-content inventory is front-loaded in the first sentence, followed by input constraints, so an agent gets the important information immediately. The trailing "No API key, no account and no sign up" is closer to promotional filler, though it does double as auth disclosure.

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?

With no output schema, the description correctly compensates by enumerating the returned fields, and it discretely covers both parameters and the size ceiling. Remaining gaps—truncation behavior at the 5000-note limit, supported SMF format handling, and error cases—are minor for a two-parameter read tool whose safety profile is already in annotations.

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 coverage is 100%, so the baseline is 3, but the description adds the one-of relationship between the two parameters that the schema does not express (required list is empty, additionalProperties false). It also states the union constraint of a 1 MiB file, which frames how the two inputs relate—modest but genuine added meaning.

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?

States a specific verb and resource ("Read a Standard MIDI File") and then enumerates exactly what comes back: format, tracks, tempos, time and key signatures, track names, programs, and notes with start and length in seconds. This is clearly distinguished from the write-side sibling create_midi and from generic readers like read_stored_file.

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?

Gives a concrete input constraint ("Give midi_base64 or storage_id for a file of at most 1 MiB") which implicitly tells the agent how to call it, but never states when to prefer this over alternatives such as read_stored_file or when a file is too large to bother. Usage is implied by the size limits rather than spelled out as when/when-not guidance.

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