session_update

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

Annotations already declare this a non-destructive, idempotent write, and the description adds the useful behavioral fact that a session is bound by default. It does not disclose the key remaining trait for a write tool: whether passing new findings replaces or appends to previously recorded interim findings, which matters given idempotentHint=true.

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?

Two tight sentences with zero filler; the core action is front-loaded and the parameter default is stated immediately after. Nothing here could be cut without losing information.

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 three-parameter write tool with no output schema, the description covers purpose and session binding adequately and the schema carries the parameter detail. The one real gap is the overwrite-vs-append semantics of repeated updates, which an agent needs in order to call this correctly over a session's lifetime.

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 session, findings, and session_id including the precedence of session_id. The description's 'uses the bound session unless you pass one' restates the schema default rather than adding syntax or edge-case detail, so baseline 3 is appropriate.

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 ('Record') and resource ('interim progress on the current session') with a parenthetical clarifying what is stored ('working findings so far'). It is distinguishable from session_start/session_end, but does not say how it differs from other note-recording siblings like memory_write, memory_append, or notes_append.

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 second sentence gives real guidance on the session parameter ('Uses the bound session unless you pass one'), which implies the common case. However, there is no explicit statement of when to use this tool versus memory_write/notes_append or session_start/session_end, so usage is only loosely implied.

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