What is mssql-extension CLAUDE.md?

Repository guidance for developing a DuckDB extension that connects to Microsoft SQL Server using C++ and the TDS network protocol. It covers the code structure, supported systems, security, versioning, and commands.

Use it when adding features, fixing bugs, building, testing, or reviewing the DuckDB-to-SQL Server connection code.

It gives a coding agent the project rules it needs before changing this extension, reducing mistakes in its architecture, compatibility, and build setup.

How hugr-lab/mssql-extension configures Claude Code

Reuse

Borrowing it

Nothing to install: this file belongs to hugr-lab/mssql-extension. Take a copy, put it at the same path in your own repository, and replace the rules that are about this project with yours.

Copy the file

curl -O https://raw.githubusercontent.com/hugr-lab/mssql-extension/main/CLAUDE.md

Clone the repo

git clone --depth 1 https://github.com/hugr-lab/mssql-extension

Made for: Claude Code.

Wrote this? Show the measurements

A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.

README.md

[![agentmods](https://agentmods.dev/badge/instructions/hugr-lab/mssql-extension/claude-md/github.svg)](https://agentmods.dev/instructions/hugr-lab/mssql-extension/claude-md)

Your own site

<a href="https://agentmods.dev/instructions/hugr-lab/mssql-extension/claude-md"><img src="https://agentmods.dev/badge/instructions/hugr-lab/mssql-extension/claude-md/github.svg" alt="Measured on agentmods" height="20"></a>

Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.

Your own site · 80×15

<a href="https://agentmods.dev/instructions/hugr-lab/mssql-extension/claude-md"><img src="https://agentmods.dev/badge/instructions/hugr-lab/mssql-extension/claude-md.svg" alt="Reviewed on agentmods" width="80" height="20"></a>

Per session 26,686 This file is loaded in full into every session.

When invoked 26,686 The same file — it is already loaded in full.

Security scan A 0 findings. A grade says what 26 rules found in the file — not that it is safe.

Origin original No closer match found in the catalogue.

Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

Model	Per session	Once invoked
Fable 5.1	$0.26686	$0.26686
Opus 5.5	$0.10674	$0.10674
Sonnet 5.5	$0.05337	$0.05337
Haiku 4.5	$0.02669	$0.02669

Measured 2d ago against content hash fd8f5e4dcd95, method: parsed. Prices are Anthropic first-party input rates as of 2026-10-07, from the pricing page.

Security

Grade A, and why

mssql-extension CLAUDE.md scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 2d ago.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Nothing flagged

None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.

CLAUDE.md · 426 lines

How it starts

The opening of the file, as written. The whole thing — 426 lines — stays where its author put it; the contents beside it link to each section on GitHub.

mssql-extension Development Guidelines

DuckDB extension for SQL Server via a custom TDS protocol implementation (no FreeTDS/ODBC).

Technology

Language: C++17 (DuckDB extension standard)
DuckDB: v2.0-cyanoptera, DuckDB's v2.0 pre-release stabilisation branch (2.0 API track, spec 069). Tracked instead of main since the branch was cut on 2026-09-03: it is where the 2.0 line is being stabilised, and main has already diverged from it. The 1.5.x world lives on branch duckdb-v1.5.5 for 0.2.x maintenance releases; main compiles against the pinned duckdb submodule SHA only (no dual-API shim since spec 069 retired mssql_compat.hpp)
TLS: OpenSSL via vcpkg (statically linked, symbol visibility controlled)
Platforms: Linux (GCC), macOS (Clang), Windows (MSVC, MinGW/Rtools 4.2)

Project Structure

src/
  azure/                # Azure AD authentication infrastructure
  catalog/              # DuckDB catalog integration + transaction manager
  codec/                # Per-type-family codec layer (spec 045): boolean/integer/
                        # float/decimal/money/string/binary/datetime/uuid. Each
                        # <family>_codec.cpp owns EncodeToBcp / DecodeFromTds /
                        # FormatSqlLiteral / FormatDdlTypeName for its types.
                        # literal_format.cpp + type_family.cpp are the dispatchers.
  connection/           # Connection pooling, provider, settings
  dml/                  # DML operations
    insert/             # INSERT (batched VALUES, OUTPUT INSERTED for RETURNING)
    update/             # UPDATE (rowid-based, VALUES JOIN pattern)
    delete/             # DELETE (rowid-based, VALUES JOIN pattern)
  include/              # Headers (mirrors src/ layout)
  query/                # Query execution and result streaming
  table_scan/           # Table scan with filter/projection pushdown
  tds/                  # TDS protocol implementation
    auth/               # Authentication strategies (SQL auth, FEDAUTH)
    encoding/           # Type encoding (datetime, decimal, GUID, UTF-16)
    tls/                # TLS via OpenSSL with custom BIO callbacks
test/
  sql/                  # SQLLogicTest files (require SQL Server for most)
    attach/             # ATTACH/DETACH tests
    azure/              # Azure AD authentication tests (no SQL Server required)
    catalog/            # Catalog, DDL, filter pushdown, statistics
    copy/               # COPY TO MSSQL (BulkLoadBCP) tests
    ctas/               # CREATE TABLE AS SELECT tests
    dml/                # UPDATE and DELETE tests
    insert/             # INSERT tests
    integration/        # Core integration (pool, TLS, large data)
    query/              # Query-level tests
    rowid/              # Rowid pseudo-column tests
    tds_connection/     # TDS protocol tests
    transaction/        # Transaction management tests
  cpp/                  # C++ unit tests (no SQL Server required)
docs/                   # Architecture documentation (see docs/architecture.md)
docker/                 # SQL Server container and Linux CI build

Read the full file on GitHub · 426 lines

Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

2d ago Changed · +1 lines · +174 tokens per session fd8f5e4dcd95
10d ago Changed · +1,151 tokens per session b9cd8508fde4
11d ago Changed · +882 tokens per session 961f9ab1154e
12d ago Changed · +2 lines · +1,858 tokens per session a146216fda06
13d ago Changed · +1 lines · +169 tokens per session b4f83d7b82cd
14d ago Changed · +125 tokens per session 61f2f882522f
15d ago Changed · +2 lines · +1,005 tokens per session cbfe9ddf8124
16d ago Changed · +2 lines · +943 tokens per session f2a8e809d061
18d ago Changed · +2 lines · +608 tokens per session c4e8083c2329
22d ago First seen · 416 lines · 19,771 tokens per session scan A e568a42f79ba

Subscribe to this mod's changes

mssql-extension CLAUDE.md is an instructions file published in the GitHub repository hugr-lab/mssql-extension (135 stars, last pushed 2d ago), licensed MIT. It adds 26,686 tokens to every session, about $0.1067 per session on Opus 5.5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.

MSSQL duckdb duckdb-extension hugr sql sqlserver

vscode buildNext.instructions.md

Working notes and architecture documentation for the new esbuild-based build system in build/next. Use when making changes to the new build pipeline (transpile/bundle commands, NLS plugin, source-map handling, resource copying, or self-hosting watch tasks).

microsoft/vscode · 9,715 tokens

mssql-extension: Instructions file for Claude Code

Borrowing it

Wrote this? Show the measurements

What it costs to keep this loaded

Grade A, and why

Nothing flagged

How it starts

mssql-extension Development Guidelines

Technology

Project Structure

What this file has done since we first saw it

Other instructions, from other repositories

vscode buildNext.instructions.md

next.js AGENTS.md

vscode oss-third-party-notices.instructions.md

langchain AGENTS.md

vscode copilot-instructions.md

deepseek-harness AGENTS.md