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`CLAUDE_CODE_MAX_MCP_DESCRIPTION_LENGTH`

env in the build documented JSON

A Claude Code environment variable, read out of the shipped bundle. It has been in the build since v2.1.280, including the newest one read.

Maximum length in characters of each MCP tool description and each MCP server's instructions that Claude Code sends to the model (default: 2048). Claude Code [truncates longer text](/docs/en/mcp#for-mcp-server-authors). Accepts a positive whole number in plain digits. Anything else is ignored and the default applies. Requires Claude Code v2.1.280 or later

Anthropic's own wording. Read off Environment variables, captured 2026-09-23.

First seen v2.1.280 22 Sep 2026

Last seen v2.1.280 22 Sep 2026

Builds1 / 123on this box, as of v2.1.280

Written about v2.1.280 first named in a changelog, 22 Sep 2026

v2.1.280in the build not in the build never minedv2.1.280

In the changelogs

Releases whose published page names CLAUDE_CODE_MAX_MCP_DESCRIPTION_LENGTH.

v2.1.280 22 Sep 2026
MCP output/description truncation length now overridable via env var
MCP output and description truncation length is now configurable via CLAUDE_CODE_MAX_MCP_DESCRIPTION_LENGTH

found in this entry's text, named in this entry

First cited

The earliest release whose published evidence quoted CLAUDE_CODE_MAX_MCP_DESCRIPTION_LENGTH was v2.1.280, 22 Sep 2026. That is the oldest release this project wrote about it, so it is a floor on the name's age and not the release that introduced it. It is not a presence reading: which builds carried the name is the table below.

ReleaseDateThe span that was quoted

v2.1.28022 Sep 2026CLAUDE_CODE_MAX_MCP_DESCRIPTION_LENGTH

Presence across releases

BuildsHow manyDatesReading

v2.1.2801 build22 Sep 2026 ◆in the build

Build by build

One row per release since the first build this name was read out of. Absent means the build was read and the name was not in it, never mined means no bundle for that release was ever archived, and a declared type or a default is only ever what that release's own bundle stated.

BuildDateStateThe record behind it

v2.1.28022 Sep 2026·addedverdict: added · int

Read out of the published npm bundle release by release, and out of Anthropic's own documentation as this site captured it. Nothing on this page is a description anybody here wrote about what the environment variable does. All environment variables.

Names beside it

Every environment variable in the inventory starting claude_code_max, up to twelve of them.

CLAUDE_CODE_MAX_CONCURRENT_SUBAGENTS v2.1.217
How many [subagents](/docs/en/sub-agents#concurrent-subagent-limit) can be running in one session before the Agent tool refuses to spawn another (default: 20). Accepts a positive whole number in plain digits; anything else is ignored, so the variable can adjust the cap but can't disable it. Requires Claude Code v2.1.217 or later
CLAUDE_CODE_MAX_CONTEXT_TOKENS v2.1.138
Override the context window size Claude Code assumes for the active model. As of v2.1.193, how it applies depends on how Claude Code resolves the model ID; see [Correct the window for a gateway or custom model ID](/docs/en/model-config#correct-the-window-for-a-gateway-or-custom-model-id). Use this when routing to a model through ANTHROPIC_BASE_URL whose context window does not match the built-in size for its name
CLAUDE_CODE_MAX_EFFORT_REMINDER v2.1.280
A new reminder can appear in the status line when effort is set to max, pointing you to /effort to change it
CLAUDE_CODE_MAX_OUTPUT_TOKENS v2.1.138
Set the maximum number of output tokens for most requests. Defaults and caps vary by model; see [max output tokens](https://platform.claude.com/docs/en/about-claude/models/overview#latest-models-comparison). Claude Code defaults to 32000 for model IDs it doesn't recognize, such as gateway-specific names, and lowers values above a model's cap to the cap. Increasing this value reduces the effective context window available before [auto-compaction](/docs/en/costs#reduce-token-usage) triggers
CLAUDE_CODE_MAX_RETRIES v2.1.138
Override the number of times to retry failed API requests (default: 10). Capped at 15 as of v2.1.186; as of v2.1.199, CLAUDE_CODE_RETRY_WATCHDOG raises the default and removes the cap. For unattended sessions that need to wait through longer outages, set CLAUDE_CODE_RETRY_WATCHDOG instead
CLAUDE_CODE_MAX_SUBAGENT_SPAWN_DEPTH v2.1.217
Number of [subagent layers](/docs/en/sub-agents#let-subagents-spawn-their-own-subagents) allowed below the main conversation (default: 3). At the default, subagents can spawn their own subagents, and a subagent at the third layer can't spawn further; set 1 to turn nesting off. In v2.1.217 through v2.1.218, the default was 1, so a subagent couldn't spawn its own unless you raised the limit; v2.1.219 raised the default to 3. Accepts a positive whole number in plain digits; anything else is ignored, so the limit can be adjusted but not removed. Requires Claude Code v2.1.217 or later
CLAUDE_CODE_MAX_SUBAGENTS_PER_SESSION v2.1.212
Removed in v2.1.224 and now a no-op. Previously capped the total number of [subagents](/docs/en/sub-agents) Claude could spawn with the Agent tool in one session (default: 200); spawning past the cap failed with Subagent spawn limit reached. The [concurrent subagent limit](/docs/en/sub-agents#concurrent-subagent-limit) and the [depth limit](/docs/en/sub-agents#let-subagents-spawn-their-own-subagents) still apply
CLAUDE_CODE_MAX_TOOL_USE_CONCURRENCY v2.1.138
Maximum number of read-only tools and subagents that can execute in parallel (default: 10). Higher values increase parallelism but consume more resources
CLAUDE_CODE_MAX_TURNS v2.1.139
Cap the number of agentic turns when no explicit limit is passed. Equivalent to passing [--max-turns](/docs/en/cli-reference#cli-flags), which takes precedence when both are set. A value that is not a positive integer is rejected at startup with an error rather than treated as no cap
CLAUDE_CODE_MAX_WEB_SEARCHES_PER_SESSION v2.1.212
Cap on the total number of [WebSearch](/docs/en/tools-reference#websearch-tool-behavior) calls one session can make (default: 200). When Claude reaches the cap, further WebSearch calls return a notice telling it to continue with the information it already gathered. Accepts a positive whole number with no upper bound. Anything else is ignored and the default applies, so the cap can be raised but not turned off. Requires Claude Code v2.1.212 or later

Documentation pages 3

Environment variablesreference tableClaude Code CLI
Claude Code changelogmentions itClaude Code CLI
Connect Claude Code to tools via MCPmentions itClaude Code CLI

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