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

The description adds meaningful behavioral context beyond the annotations: it warns about invalid JSON from raw appends, clarifies that it only handles text files, and provides concrete lock-retry guidance ('retry briefly; if it remains locked, report error.details including the lock owner and message'). This enriches the agent's understanding of edge cases and error handling.

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 three sentences with a clear front-loaded purpose, followed by caveats and then lock behavior. Every sentence earns its place, and there is no redundant restating of schema fields or annotations.

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 an output schema present and annotations covering safety, the description covers the key behavioral caveats: text-only, non-parsing, JSON invalidity risk, and lock handling. It does not explicitly state behavior for a missing file or invalid bucket, but 'existing text file' and the detailed lock guidance keep it substantially complete for a mutation tool of this complexity.

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%, so the schema already documents all five parameters in detail. The description adds minor color around file types and the meaning of 'content' being UTF-8, but it does not substantially enhance parameter understanding beyond the schema, meriting the baseline score.

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 a specific verb and resource: 'Append UTF-8 text to an existing text file in a bucket,' and lists example formats (txt, md, csv, jsonl, js/code). It also differentiates itself by explicitly stating it is not a binary-file API and does not parse CSV or JSON, which distinguishes it from sibling tools like bucket_file_write and bucket_file_read.

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 gives clear when-to-use context: appending to existing text files, with concrete format examples. It explicitly states what it is not for (binary files, parsing CSV/JSON) and warns about invalid JSON. However, it does not name a specific alternative tool for overwriting or binary operations, so it stops short of fully explicit exclusion guidance.

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