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

Goes well beyond the readOnlyHint annotation: it discloses the return shape (text/JSON as `text`, otherwise base64 plus mimetype), a hard 5MB cap that errors rather than truncating, the required files:read scope, and a reconnect hint. With no output schema, this return-format and failure-mode disclosure is exactly the value the description must add.

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?

Three tightly packed sentences with zero filler, leading with what is read and the id form, then return format, then constraints and permissions. Every clause carries information an agent needs.

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 read-only fetch tool with no output schema and only a readOnlyHint annotation, the description covers input provenance, return encoding, size limits and their failure mode, auth requirements, and a connection caveat. Nothing material to correct invocation is missing.

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 both account and file_id are already documented with the same example the description repeats. The description adds only the provenance of file_id ('from a message that carried a file'), which is minor; baseline 3 applies when the schema does the heavy lifting.

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 file posted in Slack') plus the required identifier format, so the agent knows exactly what it fetches. It does not, however, distinguish itself from nearby siblings such as read_file_content, download_file_content, or get_file_metadata, which an agent could easily confuse it with.

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 concrete usage context: the id must come from a message that carried a file, the tool needs files:read, and a reconnect is required for older workspaces. It never names an alternative tool or an explicit 'use X instead' rule, so guidance is clear but not routing-complete.

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