CLAUDE_CODE_MAX_MCP_DESCRIPTION_LENGTH and Sume server instructions

Claude Code 2.1.280 added CLAUDE_CODE_MAX_MCP_DESCRIPTION_LENGTH, which changes the 2,048-character cap on MCP tool descriptions and server instructions. Sume's server instructions constant is far longer than 2,048 characters, so rely on tools_list and tools_schema for the live contract rather than on the instructions text.

Cap and variable from the Claude Code changelog; Sume behavior from MCP tools and gates and the MCP server source, read 2026-10-01.

What is capped?

Per the changelog, the cap covers both tool descriptions and server instructions, for every MCP server in the session. The setting changes the default of 2,048 characters. It does not say whether text over the cap is cut or dropped, so test that with your own server before you depend on it.

How long are Sume's descriptions and instructions?

The server returns instructions in its initialize response. The source file holding the base instruction text is about 10,000 characters, many times the default cap. Tool descriptions are different: the assets description file says to cap each at roughly 0.5 to 2 KB and to keep longer material in on-disk skills or server instructions.

Where does the full contract live?

The docs say to discover the live contract with tools_list and tools_schema and not to assume HTTP API parity. Their example instruction is to call tools_schema with the name generate_image and explain idempotency_key and dry_run before submitting any paid generation. That keeps the rules out of the truncation path.

claude mcp add --transport http sume https://mcp.sume.com/mcp
claude mcp login sume
# then ask Claude:
# Call tools_schema with name "generate_image" and explain
# idempotency_key and dry_run before submitting any paid generation.

Should I raise the cap?

Only if you have a reason. Setting the variable higher spends more of the context window on every turn. Changing it does not change what Sume enforces: paid and write tools still need idempotency_key, and the instructions row shows in context as covered in Claude Code context: MCP server instructions.