MCP server for building with the Claude API: probe-verified model reference, request linter and fixer, cost estimates, agent scaffolding, plus live messages, token counting, batches, files and Managed Agents.
An MCP server for building with the Claude API. It gives an agent two things:
Not affiliated with Anthropic. "Claude" is a trademark of Anthropic, PBC.
Requires Node.js 20 or newer.
skills download @spboucher/claude-api-mcp --extract ./claude-api-mcp # or download the archive and verify its SHA-256
cd claude-api-mcp
npm ci # installs @anthropic-ai/sdk, @modelcontextprotocol/sdk and zod from the lockfile
npm test # offline tests, no key needed
Register it (use the absolute path of server.mjs):
# Claude Code
claude mcp add --transport stdio --env ANTHROPIC_API_KEY=$ANTHROPIC_API_KEY claude-api -- node /abs/path/claude-api-mcp/server.mjs
# Codex: ~/.codex/config.toml
[mcp_servers.claude-api]
command = "node"
args = ["/abs/path/claude-api-mcp/server.mjs"]
env_vars = ["ANTHROPIC_API_KEY"]
// Cursor: .cursor/mcp.json
{ "mcpServers": { "claude-api": { "type": "stdio", "command": "node", "args": ["/abs/path/claude-api-mcp/server.mjs"], "env": { "ANTHROPIC_API_KEY": "${env:ANTHROPIC_API_KEY}" } } } }
The key is optional: the ten offline tools work without it.
| Variable | Purpose | Default |
|---|---|---|
ANTHROPIC_API_KEY | Key for the live tools. Read from the environment, never returned in any output | none |
CLAUDE_API_MCP_MAX_OUTPUT_TOKENS | Spend guard: largest max_tokens the server will send | 32000 |
CLAUDE_API_MCP_FILE_ROOT | Only directory file_upload may read from | working directory |
Offline (no key, no cost)
| Tool | What it does |
|---|---|
model_reference | Context window, output cap, prices, thinking modes, effort levels, forced tool choice, prefill, sampling, betas, server tools — per model or as a table |
recommend_model | Model and effort for a task, honouring hard requirements |
lint_request | Findings for a Messages request, each with a fix and the API error text observed |
fix_request | Applies the mechanical fixes and reports what changed |
migrate_request | Rewrites a request for another model and lists what to review |
estimate_cost, compare_costs | Cost with cache reads/writes, batch discount, fast mode, long-prompt rates |
scaffold_agent | Runnable starters: single call, streaming, structured output, manual tool loop, tool runner, batch, Managed Agent — TypeScript or Python |
explain_error | Maps a status or message to a cause and a fix |
feature_guide | Short guidance on 15 topics |
Live
| Tool | Notes |
|---|---|
list_models, get_model, count_tokens | Free |
create_message | Billed. Linted first; nothing is sent if the API would reject it. auto_fix applies fixes. Betas go in request.betas |
extract_structured | Billed. Returns parsed JSON matching your schema |
batch_create, batch_get, batch_list, batch_results, batch_cancel | Half price; results keyed by custom_id |
file_upload, file_list, file_get, file_delete | Uploads are confined to the file root |
agent_*, environment_*, session_* | Managed Agents (beta). session_run never approves a tool call by itself |
Destructive tools (file_delete, batch_cancel, *_archive) refuse to act without confirm: true.
probes/probe.mjs and probes/probe2.mjs send small requests to every model the key can see.
Raw results: probes/matrix.json, probes/matrix2.json. probes/build-knowledge.mjs derives
knowledge.json from them. Prices come from the official pricing page (read 2026-11-10 UTC).test/offline.test.mjs asserts that the linter predicts accept/reject exactly as the API did
for every recorded outcome (30 shapes × 15 models), and that the fixer yields acceptable requests.test/run-scaffolds.mjs executes every scaffold template against the API in both languages.test/live.test.mjs drives the server through the MCP protocol with the official client:
messages, tools, vision, PDF, citations, caching, web search, betas, files, batches, Managed Agents.Refresh the knowledge base yourself: ANTHROPIC_API_KEY=… npm run probe (costs a few cents to a
few dollars depending on the models your key can see), then npm test.
2026-10-21 (the SDK
default) with two legacy probes under 2023-06-01. APIs change; model_reference reports the
observation date. Re-run the probes when in doubt.response.usage and your invoice.recommend_model is a heuristic. Evaluate on your own data.The server reads the key from its environment and scrubs key-shaped strings from error messages.
It executes no model output, opens no listening port, and reads local files only for file_upload
inside the configured root. Managed Agent tool calls that need approval are surfaced, never
auto-approved.
Installing only copies or configures. Nothing is executed for you. The Skills CLI verifies the checksum before writing files.
Select a file to preview it. Files are shown as plain text and never executed.
test/run-scaffolds.mjsStatic checks are advisory. They never certify that a package is safe. Compatibility entries are publisher claims unless marked verified.
| Version | Published | Size | SHA-256 | State |
|---|---|---|---|---|
| 1.0.1latest | Nov 10, 2026 | 76 kB | 60448ca13633… | published |
| 1.0.0 | Nov 10, 2026 | 75 kB | 6067c33278a6… | published |
Fix: server exited when launched through a symlinked path. Use this version instead of 1.0.0.
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